Influence of the menstrual cycle and oral contraceptives on thermoregulatory responses to exercise in young women

Thermoregulatory responses to exercise in relation to the phase of the menstrual cycle were studied in ten women taking oral contraceptives (P) and in ten women not taking oral contraceptives (NP). Each subject was tested for maximal aerobic capacity ( ) and for 50% exercise in the follicular (F) and luteal (L) phases of the menstrual cycle. Since the oral contraceptives would have prevented ovulation a quasi-follicular phase (q-F) and a quasi-luteal phase (q-L) of the menstrual cycle were assumed for P subjects. Exercise was performed on a cycle ergometer at an ambient temperature of 24° C and relative air humidity of 50%. Rectal (T _re), mean skin ( ), mean body ( ) temperatures and heart rate (f _c) were measured. Sweat rate was estimated by the continuous measurement of relative humidity of air in a ventilated capsule placed on the chest, converted to absolute pressure (PH₂O_chest). Gain for sweating was calculated as a ratio of increase inPH₂O_chest to the appropriate increase inT _re for the whole period of sweating (G) and for unsteady-state (G_u) separately. The did not differ either between the groups of subjects or between the phases of the menstrual cycle. In P, rectal temperature threshold for sweating (T _{re, td}) was 37.85° C in q-L and 37.60° C in q-F (P < 0.01) and corresponded to a significant difference fromT _re at rest. TheT _re, andf _c increased similarly during exercise in q-F and q-L. No menstrual phase-related differences were observed either in the dynamics of sweating or in G. In NP,T _{re, td} was shorter in L than in F (37.70 vs 37.47° C,P<0.02) with a significantly greater value fromT _re at rest. The dynamics and G for sweating were also greater in L than in F. The G_u was 36.8 versus 16.6 kPa · ° C^–1 (P<0.01) while G was 6.4 versus 3.8 kPa · ° C^–1 (P<0.05), respectively. TheT _re, andf _c increased significantly more in phase F than in phase L. It was concluded that in these women performing moderate exercise, there was a greater temperature threshold and larger gains for sweating in phase L than in phase F. Intake of oral contraceptives reduced the differences in the gains for sweating making the thermoregulatory responses to exercise more uniform.     

A testcross procedure for selecting exotic strains to improve pure-line cultivars in predominantly self-fertilizing species

Methods for identifying germplasm carrying alleles with the potential to improve a particular single-cross hybrid have been proposed and discussed in recent years. There is a need for similar methods to be used in breeding crops for which pure-line cultivars, rather than hybrids, are the goal. The objective of this research was to develop a method to identify germplasm lines with the potential to contribute favorable alleles not present in a specified pure line or set of pure lines. Given a set of adapted pure lines (A ₁, A ₂ ..., A _m) to be improved and a set of germplasm lines (P ₁ P ₂ ..., P _f), the procedure consists of producing all f x m possible hybrids and evaluating them along with the parents. The testcross statistic T _ij is defined by T _ij=(F _ij–A _j)+(1–) (F _ij–P _i), where A _j, P _i, and F _ij represent the performance of thej ^th adapted line, the i ^th germplasm line, and their hybrid, respectively. The statistic is the mean value of T _ij over all adapted parents A _j. If =(1/2)(1+d), where d = the mean degree of dominance, then T _ij measures the potential for alleles from P _i to improve A _j and measures the potential for alleles from P _i to improve the set A ₁, A ₂ ..., A _m. Use of data on soybean and peanut hybrids published by other researchers suggests that the value assumed for d has little effect on the P _i chosen. The ability of the T _ij and statistics to identify germplasm strains carrying rare favorable alleles should be assessed in empirical studies.Joint contribution: OARDC (Journal Articale No. 161-94), USDAARS, Iowa Agriculture and Home Economics Expriment Station (Journal Paper No. J-16109; Project 2985), and Agreculture and Agri-Food Canada. Salaries and research support for S. K. St. Martin Provided by state and federal funds appropriated to the Ohio Agricultural Research and Development Center, Ohio State University     

DPT tautomerisation of the wobble guanine·thymine DNA base mispair is not mutagenic: QM and QTAIM arguments

We have shown for the first time, connecting QM methods with QTAIM analysis and using the methodology of the sweeps of the energetical, electron-topological and geometrical parameters, that the tautomerisation of the wobble guanine·thymine (wG·T) DNA base mispair into the wG^*·T^* base mispair induced by the double proton transfer (DPT), which undergoes a concerted asynchronous pathway, is not mutagenic. The wG·T?→?wG^*·T^* DPT tautomerisation does not result in the transition of the G base into its mutagenic tautomeric form G^* able to mispair with the T base within the Watson–Crick base pairing scheme. This observation is explained by the so-called quantum protection of the wG·T DNA base mispair from its mutagenic tautomerisation – the dynamical non-stability of the tautomerised wG^*·T^* base mispair and significantly negative value of the Gibbs free energy of activation for the reverse reaction of the wG·T?→?wG^*·T^* DPT tautomerisation.     

Synthesis of 2H,13C-Labelled 2′-Deoxynucleosides and Their Site Specific Incorporation into Oligo-DNA for Structural Studies via Relaxation Time Measurements

Abstract

We have recently shown¹ the usefulness of ²H, ¹³C-labelled 2′-deoxynu-cleoside building blocks for structural studies via relaxation time measurements. The synthesis of phosphoramidite blocks 11 and 12 for their site-specific incorporation (indicated by underlines) into the d⁵′(¹C²G³ A ⁴ T ⁵ T ⁶ A ⁷ A ⁸ T ⁹C¹⁰G)₂ ³′ is briefly described for studying the T₁ and T_1[sgrave] relaxations of ²H and ¹³C at specific deuterated carbons in a large molecule.     

Selectively 13C-enriched DNA: Evidence from 13C1′ relaxation rate measurements of an internal dynamics sequence effect in the lac operator

Summary In order to study some internal dynamic processes of the lac operator sequence, the ¹³C-labeled duplex 5d(C₀G₁C₂T₃C₄A₅C₆A₇A₈T₉T₁₀) · d(A₁₀A₉T₈T₇G₆T₅G₄A₃G₂C₁G₀)3 was used. The spreading of both the H1 and C1 resonances brought about an excellent dispersion of the ¹H1-¹³C1 correlations. The spinlattice relaxation parameters R(C_z), R(C_x,y) and R(H_zC_z) were measured for each residue of the two complementary strands, except for the 3-terminal residues which were not labeled. Variation of the relaxation rates was found along the sequence. These data were analyzed in the context of the model-free formalism proposed by Lipari and Szabo [(1982) J. Am. Chem. Soc., 104, 4546–4570] and extended to three parameters by Clore et al. [(1990) Biochemistry, 29, 7387–7401; and (1990) J. Am. Chem. Soc., 112, 4989–4991]. A careful analysis using a least-squares program showed that our data must be interpreted in terms of a three-parameter spectral density function. With this approach, the global correlation time was found to be the same for each residue. All the C1-H1 fragments exhibited both slow (_s = 1.5) and fast (_f = 20 ps) restricted libration motions (S _inf2 ^sups =0.74 to 1.0 and S _inf2 ^supf =0.52 to 0.96). Relaxation processes were described as governed by the motion of the sugar relative to the base and in terms of bending of the whole duplex. The possible role played by the special structure of the AATT sequence is discussed. No evident correlation was found between the amplitude motions of the complementary residues. The 5-terminal residues showed large internal motions (S²=0.5), which describe the fraying of the double helix. Global examination of the microdynamical parameters S _inf2 ^supf and S _inf2 ^sups along the nucleotide sequence showed that the adenine residues exhibit more restricted fast internal motions (S _inf2 ^supf =0.88 to 0.96) than the others, whereas the measured relaxation rates of the four nucleosides in solution were mainly of dipolar origin. Moreover, the fit of both R(C_z) and R(HzC_z) experimental relaxation rates using an only global correlation time for all the residues, gave evidence of a supplementary relaxation pathway affecting R(C_x,y) for the purine residues in the (53) G₄A₃ and A₁₀A₉T₈T₇ sequences. This relaxation process was analyzed in terms of exchange stemming from motions of the sugar around the glycosidic bond on the millisecond time scale. It should be pointed out that these residues gave evidence of close contacts with the protein in the complex with the lac operator [Boelens et al. (1987) J. Mol. Biol., 193, 213–216] and that these motions could be implied in the lac-operator-lac-repressor recognition process.     

Circadian oscillators,cell cycles,and singularities: light perturbations of the free-running rhythm of cell division inEuglena

Summary The free-running circadian rhythm of cell division in the algal flagellate,Euglena gracilis (Z) was perturbed by 3-h light signals of varying intensities imposed at different circadian times (CT). Light pulses within the range of 700 to 7,500 lux were found to yield the same strong (Type 0) phase response curve (PRC) comprising both advance and delaye phase shifts as great as 15 h. Dark signals generated a PRC of reduced amplitude with very little, if any, phase advance being observed. Light perturbations of lower intensity, however, elicited quite different responses if applied at a quite specific circadian time: A 40- to 400-lux pulse given at approximately CT 0 (late subjective night) induced total arrhythmicity, and the culture reverted to asynchronous, exponential growth. Different degrees of arryhtmicity were induced by the same low-intensity perturbations (I ^*) given slightly before or after this sensitive phase point (T ^*), but if imposed at other circadian times, they generated normal type 0 phase resetting. The demonstration of the existence of this critical pulse (T ^*,I ^*) provides further evidence that the cell division cycle ofEuglena (and presumably other microorganisms) is regulated by a circadian oscillator and, in particular, by one having limit cycle dynamics.Abbreviations LL continuous illumination - DD continuous darkness - LD light-dark cycle - LD x, y, light-dark cycle comprisingx h of light andy h of dark - t period of a LD cycle - CO circadian oscillator - CR circadian rhythm - period of a freerunning circadian rhythm in constant conditions (taken here to be the time between onsets of cell division in a population of cells - _R phase marker, or phase reference point (here, the onset of the division burst) - phase of the rhythm - change in phase (phase shift) - new phase attained after phase shift - CT circadian time (CT 0 indicates the phase point of a free-running rhythm that has been normalized to 24 h which corresponds to that occurring at the onset of light in aLD:12, 12 reference cycle) - PRC phase response curve (plot of phase shift engendered by a perturbation as a function of the circadian time of its application) - T ^*,I ^*) coordinates of an annihilating (light) stimulus given at a critical circadian time (T ^*, corresponding to the singularity point) and having a critical strength (I ^*) - CDC cell division cycle - average generation (doubling) time of a cell population - average step-size, or factorial increase in cell titer (plateau to plateau) after a phased division burst Dedicated to Prof. Colin S. Pittendrigh on only his 65th birthday     

A new technique for continuous measurement of the heat of fermentation

Summary A special temperature control system has been developed and applied to continuous measuring of the heat evolved during a fermentation process. In this system, the fermentation broth was overcooled by a given constant cooling water flow. The excess heat removed from the fermentor was then made up by an immersion electrical heater. The action of the temperature controller was precisely monitored as it varied in response to the amount of heat produced by the microbial activities.The technique was used for determining the heat evolution byEscherichia coli grown on glucose. The ratio between quantities of total heat release and total oxygen consumption has been determined to be 0.556 MJ/mol O₂.The newly developed technique can be employed as an online sensor to monitor the microbial activities of either aerobic or anaerobic fermentation systems.Symbols C_c Heat capacity of cooling water (MJ/kg · °C) - C_p Heat capacity (MJ/kg · °C) - I Current of immersion heater (A) - K Constant in Equation (2) (h) - K Constant in Equation (13) (m³ · h · °C/MJ) - Q_c Flow rate of cooling water (m³/h) - Heat of agitation (MJ/m³ · h) - Heat dissipated by the bubbling gas (MJ/m³ · h) - Heat removal by the action of controller (MJ/m³ · h) - Heat of fermentation (MJ/m³ · h) - Heat loss to the surroundings (MJ/m³ · h) - Q_pass Constant average power dissipated by the immersion heater (MJ/m³ · h) - Fluctuating power dissipated by the immersion heater (MJ/m³ · h) - Power dissipated by the immersion heater (MJ/m³ · h) - T Temperature of fermentation broth (°C) - Constant average temperature of fermentation broth (°C) - Fluctuating temperature of fermentation broth (°C) - T_a Temperature of the ambient air (°C) - T_c Inlet temperature of cooling water (°C) - U₁A₁ Specific heat transfer coefficient for determination of heat loss to the surroundings (MJ/m³ · h · °C) - U₂A₂ Specific heat transfer coefficient for cooling surfaces (MJ/m³ · h · °C) - U₃A₃ Constant in Equation (16) (MJ/m³ · h · °C) - V Voltage of immersion heater (V) - V_L Liquid volume (m³) - OUR Oxygen uptake rate (mol O₂/m³ · h) Greek Letters H_fo The ratio between the total heat release and the total oxygen uptake (MJ/mol O₂) - _c Density of cooling water (kg/m³) - Time constant defined in Equation (6) (h) - _iM_iC_pi Heat capacity of system components (fermentation broth + fermentor jar + stainless steel) (MJ/m³ · °C)     

Analysis of gas exchange in seedlings of Acer saccharum: integration of field and laboratory studies

In the field, photosynthesis of Acer saccharum seedlings was rarely light saturated, even though light saturation occurs at about 100 mol quanta m^-2 s^-1 photosynthetic photon flux density (PPFD). PPFD during more than 75% of the daylight period was 50 mol m^-2 s^-1 or less. At these low PPFD's there is a marked interaction of PPFD with the initial slope (CE) of the CO₂ response. At PPFD-saturation CE was 0.018 mol m^-2 s^-1/(l/l). The apparent quantum efficiency (incident PPFD) at saturating CO₂ was 0.05–0.08 mol/mol. and PPFD-saturated CO₂ exchange was 6–8 mol m^-2 s^-1. The ratio of internal CO₂ concentration to external (C _i /C _a ) was 0.7 to 0.8 except during sunflecks when it decreased to 0.5. The decrease in C _i /C _a during sunflecks was the result of the slow response of stomates to increased PPFD compared to the response of net photosynthesis. An empirical model, which included the above parameters was used to simulate the measured CO₂ exchange rate for portions of two days. Parameter values for the model were determined in experiments separate from the daily time courses being sumulated. Analysis of the field data, partly through the use of simulations, indicate that the elimination of sunflecks would reduce net carbon gain by 5–10%.List of symbols A measured photosynthetic rate under any set of conditions (mol m^-2 s^-1) - A _m (atm) measured photosynthetic rate at saturating PPFD, 350 l/l CO₂ and 21% (v/v) O₂ (mol m^-2 s^-1) - C constant in equation of Smith (1937, 1938) - C _a CO₂ concentration in the air (l/l) - C _i CO₂ concentration in the intercellular air space (l/l) - C _i ^/* C _i corrected for CO₂ compensation point, i.e., C _i -I ^*, (l/l) - CE initial slope of the CO₂ response of photosynthesis (mol m^-2 s^-1/(l/l)) - CEM CE at PPFD saturation - E transpiration rate (mmol m^-2 s^-1) - F predicted photosynthetic rate (mol m^-2 s^-1) - G leaf conductance to H₂O (mol m^-2 s^-1) - I photosynthetic photon flux density (mol m^-2 s^-1) - N number of data points - P _m predicted photosynthetic rate at saturating CO₂ and given PPFD (mol m^-2 s^-1) - P _ml predicted photosynthetic rate at saturating CO₂ and PPFD (mol m^-2 s^-1) - R _d residual respiratory rate (mol m^-2 s^-1) - T _a air temperature (°C) - T _l leaf temperature (°C) - V reaction velocity in equation of Smith (1937, 1938) - V _max saturated reaction velocity in equation of Smith (1937, 1938) - VPA vapor pressure of water in the air (mbar/bar) - VPD vapor pressure difference between leaf and air (mbar/bar) - X substrate concentration in equation of Smith (1937, 1938) - initial slope of the PPFD response of photosynthesis at saturating CO₂ (mol CO₂/mol quanta) - (atm) initial slope of the PPFD response of photosynthesis at 340 l/l CO₂ and 21% (v/v) O₂ (mol CO₂/mol quanta) - I ^* CO₂ compensation point after correction for residual respiration (l/l) - PPFD compensation point (mol m^-2 s^-1)     

Perception of effort during high-intensity exercise at low, moderate and high wet bulb globe temperatures

The purpose of this study was to determine the effect of low, moderate and high wet bulb globe temperatures (T _wbg) on cardiovascular variables and ratings of perceived exertion (RPE) during moderately prolonged, high-intensity exercise. Six subjects [four men and two women; mean (SD) age, 22.0 (1.2) years; maximum oxygen consumption ({ie519-1}), 51.0 (8.4) ml · kg^–1 · min^–1] completed 30 min of exercise (80% {ie519-2}) on a cycle ergometer at low [14.7 (2.1)°C], moderate [21.0 (1.5)° C], and high [27.4 (2.3)° C]T _wbg. Two additional subjects completed 20 min of exercise in the high temperature condition, but completed 30 min in the moderate and lowT _wbg. Heart rate (f _c), blood pressure, blood lactate (La), mean skin temperature ( _sk), , and RPE were measured at 10, 20 and 30 min. Results showed thatf _c, rate pressure product, RPE, pulmonary ventilation and ventilatory equivalent for oxygen increased (P < 0.05) across time for all conditions, while decreased across time. _sk andf _c were significantly greater across time in the high condition [35.9 (0.65)° C; 176 (12.6) beats · min^–1] compared to the moderate [34.6 (1.5)° C; 170 (17.2) beats · min^–1] and the low condition [31.7 (1.5)° C; 164 (17.1) beats-min^–1]. However, there were no differences throughout exercise in RPE [high,.16.2 (2.0); moderate, 16.4 (2.2); low, 16.3 (1.9)] and across the conditions. These data suggest that RPE is closely related to metabolic intensity but is not a valid indicator of cardiovascular strain during exercise in highT _wbg conditions.     

Mathematical modeling of mixing in a horizontal rotating tubular bioreactor: “Simple flow” model

The construction of the horizontal rotating tubular bioreactor (HRTB) represents a combination of a thin-layer bioreactor and a biodisc reactor. The bioreactor was made of a plastic tube whose interior was divided by the O-ring shaped partition walls. For the investigation of mixing properties in HRTB the temperature step method was applied. The temperature change in the bioreactor as a response to a temperature step in the inlet flow was monitored by six Pt-100 sensors (t ₉₀ response time 0.08 s and resolution 0.002 °C) which were connected with an interface unit and personal computer. Mixing properties of the bioreactor were modeled using the modified tank in series concept which divided the bioreactor into ideally mixed compartments. A mathematical mixing model with simple flow was developed according to the physical model of the compartments network and corresponding heat balances. Numerical integration of an established set of differential equations was done by the Runge-Kutt-Fehlberg method. The final mathematical model with simple flow contained four adjustable parameters (N1,Ni, F _cr andF _p ) and five fixed parameters.List of Symbols A _u m² inner surface of bioreactor's wall - A _ui m² i-th part of inner surface of bioreactor's wall - A _v m² outlet surface of bioreactor's wall - A _vi m² i-th part of outlet surface of bioreactor's wall - C _p kJ kg^–1 K^–1 heat capacity of liquid - C _pr kJ kg^–1 K^–1 heat capacity of bioreactor's wall - D h^–1 dilution rate - E °C °C^–1 h^–1 error of mathematical model - F _cr dm³s^–1 circulation flow in the model - F _p dm³ s^–1 back flow in the model - F _t dm³s^–1 inlet flow in the bioreactor - I °C intensity of temperature step, the difference in temperature between the temperature of the inlet liquid flow and the temperature of liquid in the bioreactor before the temperature step - K1 Wm^–2K^–1 heat transfer coefficient between the liquid and bioreactor's wall - K2 Wm^–2K^–1 heat transfer coefficient between the bioreactor's wall and air - m _s kg mass of bioreactor's wall - L m length of bioreactor - L _k m wetted perimeter of bioreactor - n min^–1 rotational speed of bioreactor - n _s number of temperature sensors - N1 number of cascades - Ni number of compartments inside the cascade - Nu Nusselt number - Pr Prandtl number - r _u m inner diameter of bioreactor - r _v m outside diameter of bioreactor - Re Reynolds number - s(t) step function - t s time - T °C temperature - T _c °C calculated temperature - T _m °C measured temperature - T _N1,Ni °C temperature of liquid in a defined compartment inside cascade - T _N1,S °C temperature of defined part of bioreactor's wall - T _S °C temperature of bioreactor's wall - T _v °C temperature of liquid in bioreactor - T _z °C temperature of surrounding air - V _t dm³ volume of liquid in the bioreactor Greek Symbols kJm^–1s^–1 K^–1 thermal conductivity of liquid in the bioreactor - kgm^–3 density of liquid in the bioreactor - m²s^–1 kinematic viscosity of liquid in the bioreactor Matrix Coefficient B - C - D - E B+C+D - G1 - G2 - G3 - A _ui - A _vi - Q ₁ - Q ₂ - Q ₃      

Search for associations between <Emphasis Type="Italic">G/A</Emphasis> polymorphism of the <Emphasis Type="Italic">EPAS1</Emphasis> gene and the maximal oxygen consumption in Russian athletes

This study investigates associations between G/A polymorphism of the epithelial PAS domain protein 1 (EPAS1) gene (rs1867785) and the maximum rate of oxygen consumption (VO_2max) in male Russian athletes. The study engaged 241 male athletes from different sports; the control group of nonathletes included 92 subjects. Increased frequencies of the AA and AG genotypes of the EPAS1 gene (χ² = 14.16, p = 0.03) were found in the cohort of male athletes. The frequencies of these alleles in the subgroups with moderate (EPAS1*A 38.1% and EPAS1*G 61.9%) and high (EPAS1*A 41.8% and EPAS1*G 58.2%) VO_2max values significantly differed from those in the control group (χ² = 7.53, p = 0.006 and χ² = 6.58, p = 0.01, respectively). The higher aerobic capacities are probably associated with the presence of at least one minor A allele of the EPAS1 gene in the genome.     

Continuous penicillin G hydrolysis in an electro-membrane reactor with immobilized penicillin G acylase

Penicillin G (2%, w/v in phosphate buffer, pH 8) was hydrolysed in a flow-through, miniature electro-membrane reactor with the penicillin G acylase immobilized in 5% (w/v) polyacrylamide (diam. 10 mm, thickness 2.6 mm, enzyme activity 24 U ml^–1). The conversion of penicillin G increased from 0.15 to almost 0.5 when the electric current applied to the reactor was changed from –600 to +600 A/m² with a substrate residency of 1 h. Symbols and abbreviations c _j ^p & concentration of component j in product stream (M) c _j ^s & concentration of component j in substrate stream (M) c _s ^o & substrate concentration at reactor inlet (M) C _j ^p=c _j ^p/c _S ⁰ & scaled concentration of component j in product stream C _j ^s=c _j ^s/c _S ⁰ & scaled concentration of component j in substrate stream i & electric current density (A/m²) j & reaction component, j P, Q or S P & main reaction product (6-aminopenicillanic acid) PGA & penicillin G acylase Q & side reaction product (phenylacetic acid) S & substrate (penicillin G) Y _s=C _P ^s+C _P ^p & substrate conversion & mean residence time of substrate and product streams in reactor (h) =C _Q ^s+C _Q ^p+C _S ^s+C _S ^s & check-sum of scaled concentrations =C _P ^p/(C _P ^s+C _P ^p) & separation factor of 6-aminopenicillanic acid (0 1)     

The effect of ethylene on root meristems of Pisum sativum and Zea mays

Summary Ethylene at a concentration of 100 l l^–1 causes a slight increase in the duration of the mitotic cycle in the primary root meristems of both Pisum sativum L. and Zea mays L. This is due to a lengthening of the G ₁ phase; other phases of the cycle are unaffected. Autoradiography and microdensitometry show that the rate of ³H-thymidine incorporation into nuclei of Pisum is maximal when about half the DNA has been replicated, and that ethylene has no effect upon this rate. Ethylene causes a reduction of the number of dividing cells in the root meristem, particularly in Pisum.Abbreviations Duration of the S phase, the G ₁ phase, the G ₂ phase of the mitotic cell cycle, respectively - T _C Duration of the complete mitotic cell cycle - QC Quiescent centre - LI, MI Labelling index, Mitotic index (i.e. fraction of the population labelled or in mitosis, respectively) - PF Proliferative fraction (i.e. fraction of the population making progress towards mitosis) - [³H]dT tritiated thymidine     

KCl transport across an insect epithelium: II. Electrochemical potentials and electrophysiology

Summary The cellular mechanism of K-stimulated Cl transport in locust hindgut was studied using double-barrelled ionsensitive microelectrodes and electrophysiological techniques. Steady-state net electrochemical potentials for Cl and K and the conductances of apical and basal membranes and paracellular pathway were determined under control conditions, during exposure to 1mm cAMP, and following ion substitutions. Under control open-circuit conditions, intracellular Cl activity (a _Cl ^c ) was 3.5 times that predicted for passive equilibrium across the apical membrane. The net electrochemical potential opposing Cl entry from the mucosal side increased by 50% during cAMP stimulation of transepithelial Cl absorption whereas the net electrochemical potential favoring Cl exit across the basal membrane was unchanged. No correlation was observed between and the net electrochemical potential across the apical membrane for Na. The net electrochemical potential favoring K entry across the apical membrane was negligible underI _sc conditions when Cl transport rate was approximately 10 eq cm^–2 hr^–1. Locust rectal cells showed electrical and dye coupling. The results also indicate that most transepithelial diffusion of ions is transcellular and that epithelial tightness effectively increases during exposure to cAMP becauseR _a andR _b both decrease, by 80% whileR _j is unchanged. The cAMP-induced R _b was abolished in Cl-free saline whereas R _a was insensitive to Cl removal, but was blocked by removing K from the saline. Based on these findings, our model for Cl absorption in locust hindgut features i) an active entry step for Cl at the apical membrane which is stimulated by cAMP and by low levels of K on the mucosal side, but is not energized by or a large cAMP-stimulated Cl conductance in the basal membrane and a similar cAMP-stimulated K conductance in the apical membrane. cAMP dose-response curves are similar for the stimulation of active Cl absorption and Cl-independent (i. e. K) conductance, indicating that cAMP exerts dual control over active Cl transport and counter-ion permeability.     

The effect of ambient temperature on the relationship between ventilation and metabolism in a small parrot (Agapornis roseicollis)

Summary Values for basal metabolism, standard tidal volume (V _T), standard minute volume ( ), and mean extraction efficiency (EO₂) in the thermal neutral zone (TNZ) inAgapornis roseicollis (1.84 ml·min^–1; 0.95 ml·br^–1, STPD; and 33.3 ml·min^–1, STPD; and 22.5%; respectively) were all very similar to values for these parameters previously measured inBolborhynchus lineola, a similarly sized, closely related species from a distinctly different habitat.Having both a lower critical temperature (T_lc) below and an upper critical temperature (T_uc) above those ofB. lineola, the TNZ ofA. roseicollis extended from 25° to at least 35°C. The thermal conductance below the TNZ ofA. roseicollis was 14% less than that ofB. lineola. Therefore, at 5°C the standard metabolic rate (SMR) of the former is 17% less than that of the latter, and at 35°C it is 20% less. At 5°CA. roseicollis has a lower EO₂ and at 35°C a higher EO₂ than that ofB. lineola. The patterns of resting energy metabolism and of ventilation ofA. roseicollis and ofB. lineola are consistent with the former species being better suited to living in a more variable thermal environment than the latter.MeanV _T has a weak positive correlation with the rate of oxygen consumption ( ) at a constant ambient temperature (T _a) but a much stronger correlation when resting increases in response to a decrease inT _a.V _t is the only ventilatory parameter which is linearly correlated toT _a from 35° to –25°C. The data suggest thatT _a may have a regulatory effect onV _T somewhat independent of or .     

Optimum temperature policy for batch reactors performing biochemical reactions in the presence of enzyme deactivation

A necessary condition is found for the optimum temperature policy which leads to the minimum reaction time for a given final conversion of substrate in a well stirred, enzymatic batch reactor performing an enzyme-catalyzed reaction following Michaelis-Menten kinetics in the presence of first order enzyme decay. The reasoning, which is based on Euler's classical approach to variational calculus, is relevant for the predesign steps because it indicates in a simple fashion which temperature program should be followed in order to obtain the maximum advantage of existing enzyme using the type of reactor usually elected by technologists in the fine biochemistry field. In order to highlight the relevance and applicability of the work reported here, the case of optimality under isothermal operating conditions is considered and a practical example is worked out.List of Symbols C _E mol.m^–3 concentration of active enzyme - C _E ^* dimensionless counterpart of C_E - C _E,0 mol.m^–3 initial concentration of active enzyme - C _E,b mol.m^–3 final concentration of active enzyme - C _E,opt ^* optimal dimensionless counterpart of C_E - C _smol.m^–3 concentration of substrate - C _S ^Emphasis>/* dimensionless counterpart of C_S - C _S,0mol.m^–3 initial concentration of substrate - C _S,bmol.m^–3 final concentration of substrate - E enzyme in active form - E ₃ ^* dimensionless counterpart of E_a,3 - E _a,1J.mol^–1 activation energy associated with k₁ - E _a,3J.mol^–1 activation energy associated with k₃ - E _d enzyme in deactivated form - ES enzyme/substrate complex - k ₁ s^–1 kinetic constant associated with the enzyme-catalyzed transformation of substrate - k _1,0 s^–1 preexponential factor associated with k₁ - k ₂ mol^–1.m³s^–1 kinetic constant associated with the binding of substrate to the enzyme - k _–2 s^–1 kinetic constant associated with the dissociation of the enzyme/substrate complex - K _2,0 mol.m^–3 constant value of K₂ - K _2,0 ^* dimensionless counterpart of K_2,0 - k ₃ s^–1 kinetic constant associated with the deactivation of enzyme - k _3,0 s^–1 preexponential factor associated with k₃ - k _3,0 ^* dimensionless counterpart of k_3,0 - P product - R J.K^–1.mol^–1 ideal gas constant - S substrate - t s time since start-up of reaction - T K absolute temperature - T ^* dimensionless absolute temperature - T _i,opt ^* optimal dimensionless isothermal temperature of operation - T _opt ^* optimal dimensionless temperature of operation - t _b s time of a batch - t _b ^* dimensionless counterpart of t_b - t _b,min ^* minimum value of the dimensionless counterpart of t_b Greek Symbols dimensionless counterpart of C_E,0 - dimensionless counterpart of C_E,b - dummmy variable of integration - dummy variable of integration - auxiliary dimensionless variable - ^* dimensionless variation of k₁ with temperature - _i ^* dimensionless value of k₁ under isothermal conditions - _opt ^* optimal dimensionless variation of k₁ with temperature     

Concentrationo-dependence of nonelectrolyte permeability of toad bladder

Summary A theoretical formulation was derived for the dependence of bulk solute permeability,P, defined as net flux :- concentration gradient, c, across any membrane in which solute concentration is controlling for net flux, . According to this formulation, is stimulated by increments in trans concentration,c ₂, in the rangec ₂/c ₁=0.0–0.1. Net flux of urea across toad bladder down concentration gradients was shown to be stimulated threefold by small increments in trans urea concentration. The theory also predicts that, in the absence of concentration gradients, tracer permeability,P ^*, defined as tracer flux :- tracer concentration, will be independent ofc provided thatP=P ^*, but will diminish with increasingc ifP/P ^*<1.P/P ^* was not significantly different from unity for urea, and bothP andP ^* were independent ofc in the absence of concentration gradients. However,P/P ^* was significantly less than unity (0.90 and 0.85) for thiourea and mannitol, respectively. In conformity with theory,P ^* (and alsoP) of these two solutes, measured asc was increased by 3–4 orders of magnitude, diminished progressively. These effects are more consistent with this formulation than with transport via a saturable carrier.     

Start-up sensitivity to the initial state of a batch bioreactor for a recombinant Escherichia coli in a complex medium

The sensitivities with respect to the initial state of five key variables describing the performance of a batch bioreactor have been computed from an experimentally validated kinetic model. The system has a recombinant Escherichia coli strain containing the plasmid pBR Eco gap, which codes for glyceraldehyde-3-phosphate dehydrogenase (GAPDH) in a complex medium. Since previous studies have shown the start-up sensitivities to be particularly important, the initial 10% of the duration of fermentation was chosen as the time span. The sensitivities of the cell mass, GAPDH and acetate increased with time while those of glucose and yeast extract remained practically constant.Acetate has a crucial role as it functions as both a product and a reactant. With no acetate in the inoculum, the sensitivities of acetate increased an order of magnitude faster than other sensitivities. However, upon addition of acetate through the inoculum, its sensitivities decreased the fastest and stabilised beyond a starting concentration of about 1 g/l whereas other sensitivities stabilised after 5 to 6 g/l of initial acetate. A three-dimensional envelope in the space of acetate concentration-time-relative sensitivity shows a locus of concentrations for minimum time-dependent acetate sensitivity; this may be maintained through fed-batch operation.List of Symbols a A/A₀ - A g/l initial concentration at any time - A ₀ g/l initial acetate concentration - e E/E₀ - E g/l yeast extract concentration at any time - E ₀ g/l initial yeast extract concentration - g G/G₀ - G g/l glucose concentration at any time - G ₀ g/l initial glucose concentration - k _A ^A g/l inhibition constant for acetate-dependent growth during the acetate phase - k _A ^G g/l inhibition constant for acetate-dependent growth during the glucose phase - k _M ^A 1/h rate constant for acetate phase - k _M ^G 1/h rate constant for glucose phase - K _A g/1 affinity constant for acetate - K _G g/1 affinity constant for glucose - m ^A 1/h coefficient of maintenance in acetate - m _m ^A 1/h maximum value of m ^A - m ^G 1/h coefficient of maintenance in glucose - m _m ^G 1/h maximum value of m ^G - n empirical constant - P P/P₀ - P U/ml GAPDH concentration at any time - P ₀ U/ml initial GAPDH concentration - s _c (i,j) sensitivity of y _i to y _j(0) for A ₀=c - t h time - x X/X₀ - X g/l cell mass concentration at any time - X ₀ g/l initial cell mass concentration - y ₁ x - y₂ g - y₃ a - y₄ e - y ₅ p - y _x/A ^A g/g yield coefficient for cell mass per unit mass of acetate during acetate phase - y _x/A ^G g/g yield coefficient for cell mass per unit mass of acetate during glucose phase - y _x/G g/g yield coefficient for cell mass per unit mass of glucose - y _E/x ^A g/g yield coefficient for yeast extract per unit cell mass during acetate phase - y _P/x ^A g/g yield coefficient for yeast extract per unit cell mass during glucose phase - y _P/x ^A U/g yield coefficient for GAPDH per unit cell mass during acetate phase - y _P/x ^G U/g yield coefficient for GAPDH per unit cell mass during glucose phase Greek Letters ₀ proportionality constant for plasmid loss probability - ₁ 1/h maximum rate of plasmid replication - ₂ 1/h saturation constant of the host component of plasmid replication - regulation function (0 or 1) - regulation function (0 or 1) - exponent of growth inhibition term for acetate during the acetate phase - exponent of growth inhibition term for acetate during the glucose phase - ^A 1/h specific growth rate during acetate phase - _m ^A 1/h maximum value of ^A - ^G 1/h specific growth rate during glucose phase - _m ^G 1/h maximum value of ^G - _c (i,j) ratio of sensitivities, s _c (i,j)/s ₀(i,j) - nondimensional time, t _m ^G