Positive inotropic action of NMDA receptor antagonist (+)-MK801 in rat heart

(+)-MK801, a noncompetitive NMDA receptor antagonist, was reported to exhibit anticonvulsive and neuroprotective activities during the postischemic period. Intravenous administration of (+)-MK801 produced tachycardia in rats, but bradycardia in pigs. We examined the mechanical and electrophysiological effects of (+)-MK801 on rat cardiac tissues. (+)-MK801 dose-dependently increased (3–100 µM) twitch tension in rat atria and ventricular strips. The spontaneous beating rate in rat right atria, however, was dose-dependently decreased by (+)-MK801. The inotropic effect of (+)-MK801 was affected neither by ₁-antagonist (1 µM prazosin) nor by ₁-adrenoceptor antagonist (3 µM atenolol), but significantly by a transient outward K⁺ channel blocker (3 mM 4-aminopyridine). (+)-MK801 did not cause any significant change of intracellular cAMP content. Electrophysiological study in rat ventricular cells revealed that (+)-MK801 concentration-dependently prolonged the action potential duration with a concomitant decrease in the maximum rate of the action potential upstroke (V_max) and an increase in the recovery time constant of V_max. Voltage clamp study showed that (+)-MK801 (3 µM) reduced inward Na⁺ current (I_Na), along with a slowing of its recovery from inactivation and a slight negative shift of its voltage-dependent steady-state inactivation curves. At a much higher concentration (30 µM), (+)-MK801 slightly reduced the amplitude of L-type calcium inward current (I_Ca), although the voltage dependence of its steady-state inactivation was unaffected. For the potassium currents in rat ventricular cells, 3 µM of (+)-MK801 reduced the peak transient outward current (I_to), steady-state outward current (I_ss) and inward current through K₁ channels. The inhibition of I_to was associated with a prominent negative shift in the voltage dependence of its steady-state inactivation curve. The outward current through K₁ channels was unaffected. These results indicate that (+)-MK801 may be a strong I_Na and I_to blocker with some I_Ca blocking activity. The inhibition of I_to and other K⁺ efflux would prolong action potential duration, produce positive inotropic action and contribute to the negative chronotropic effect of (+)-MK801.     

Photosynthetic electron transport in thylakoids from cotton cultivars (Gossypium sp.) differing in tolerance to prometryn

A method to determine photosynthetic electron transport in thylakoid membranes is described for Gossypium barbadense (cv. Pima S-7) and G. hirsutum (cv. DP 5415). These cultivars differed markedly in tolerance to prometryn, a PS II inhibitor. The rates of photosynthetic electron transport obtained were 245 mole oxygen mg^–1 chl h¹. Plant age and leaf size influenced the activity of the thylakoid preparations. Thylakoids from leaves of plants 24 to 37 d and 50–70 mm in diameter had the highest activities; thylakoids from cotyledons, fully expanded leaves and young leaves had low activity. Thylakoids from both species had similar photosynthetic activities and I₅₀'s for prometryn, atrazine and diuron. Thus, tolerance to prometryn was not due to differential binding at D1 protein.Abbreviations PSII photosystem II - DAP day after planting - DQ duroquinone - DBMIB dibromothymoquinone - DMBQ 2,5-dimethyl-p-benzoquinone - I₅₀ concentration to inhibit reaction by 50% - Q_A quinone A - Q_B quinone B     

Modulation of inwardly rectifying Na+-K+ channels by serotonin and cyclic nucleotides in salivary gland cells of the leech,Haementeria

Summary The electrically excitable salivary cells of the giant Amazon leech, Haementeria, display a time-dependent inward rectification. Under voltage clamp, hyperpolarizing steps to membrane potentials negative to about –70 mV were associated with the activation of a slow inward current (I _h) which showed no inactivation with time. The time course of activation of I _hwas described by a single-exponential function and was strongly voltage dependent. The activation curve of_hranged from –72 to –118 mV, with half-activation occurring at –100 mV. Ion-substitution experiments indicated that I _his carried by both Na⁺ and K⁺ ions. 5-Hydroxytryptamine (5-HT) increased the amplitude of I _hand its rale of activation. It also produced a positive shift of the activation curve of the conductance underlying I _h G_hwithout altering the slope factor, thus indicating that the voltage dependence of I _hwas modulated by 5-HT. Cs⁺ blocked both I _hand the 5-HT-polentiated current in a voltage-independent manner, whereas Ba²⁺ had little effect. It is concluded that 5-HT increases I _hby modulating the inwardly rectifying Na⁺-K⁺ channels in the salivary cells. The effect of 5-HT may be mediated by an increase in adenylate cyclase activity since I _hwas increased by 8-bromocyclic AMP and by the phosphodiesterase inhibitor, 3-isobutyl-l-methylxanthine. In contrast, I _hwas reduced by 8-bromo-cyclic GMPand by zaprinast (an inhibitor of cyclic GMP-scnsitive phosphodieslerase). Cyclic GMP itself also reduced I _h, and the effect was specific to the 3,5 form; 2,3-cyclic GMP was inactive. The results suggest that the inward-rectifier channel may be modulated in opposite directions by cyclic AMP and cyclic GMPThis work was supported by a grant from the Science and Engineering Research Council (no. GR/F/17087). We are grateful to the SmithKline (1982) Foundation for provision of a pulse generator     

Effects of D-600 on sodium current in squid axons

Summary The effects of the calcium antagonist D-600 (methoxyverapamil) on the excitatory inward sodium current,I _Na, of internally perfused squid giant axons were studied under voltageclamp conditions. We observed little or no effect of the drug when it was added to the external solution at concentrations of 10–200 M. Furthermore, it did not produce a frequency, or use-dependent block ofI _Na when repetitive voltage-clamp pulses were used at rates of 2–5Hz. However, it did produce use-dependent blockade ofI _Na when it was placed internally at a concentration of 200 M. These results in conjunction with other studies suggest that D-600 is a selective blocker of calcium channels in squid axons when the drug is placed in the external solution. Its effects, when placed in the internal solution, are similar to those of permanently charged local anesthetic derivatives, which also produce use-dependent block ofI _Na.     

Identifying populations useful for improving parents of a single cross based on net transfer of alleles

Summary Theory and methods for identifying populations (P _y ) with the highest frequency of favorable dominant alleles not present in an elite single cross (I ₁× I ₂) have been developed recently. During selection, new favorable alleles can be transferred from P _y to either I ₁ or I ₂ only at the risk of losing favorable alleles already present in the single cross. A net improvement (NI) statistic, which estimates the relative number of favorable alleles that can be gained from P _y minus the relative number of favorable alleles that can be lost from I ₁ or I ₂, is presented. NI is calculated as maximum [(I ₁×P _y –I ₁×I ₂)/2,(I ₂×P _y –I ₁×I ₂)/2]. Because I ₁ × I ₂ is constant in an experiment, the method reduces to choosing P _y populations with the best mean performance in combination with either I ₁ or I ₂. For a set of maize (Zea mays L.) grain yield data, NI was highly correlated to three other statistics proposed for choosing populations, namely: (1) minimally biased estimate (l ) of the relative number of favorable dominant alleles present in P _y but not in I ₁ and I ₂; (2) minimum upper bound on l ; and (3) predicted performance of the three-way cross [P _y (I ₁× I ₂)]. While l estimates potential improvement likely to be achieved only through long-term recurrent selection, NI is probably a better predictor of short-term improvement in single-cross performance.A contribution from Lifaco Genetics, a subsidiary of Groupe Limagrain     

An alternative statistic for identifying lines useful for improving parents of an elite single cross

Summary Theory and methods for identifying inbred lines (I _w) with favorable dominant alleles not present in an elite single cross (I ₁×I ₂) have been developed recently. Selected I _w lines can be crossed to I ₁ or to I ₂ to transfer new favorable alleles to the single cross. However, favorable alleles already present in the single cross may be lost during selection. It is important to consider both potential gain of favorable alleles from I _w and loss of favorable alleles already present in I ₁×I ₂. The net improvement statistic (NI)=maximum [(I ₁×I _w-I ₁xI ₂)/2, (I ₂×I _w-I ₁×I ₂)/2] estimates the number of loci where favorable alleles can be gained minus the number of loci where favorable alleles can be lost in the single cross. Because I ₁×I ₂ is constant in an experiment, the method reduces to choosing I _w lines with the best mean performance in combination with either I ₁ or I ₁. NI was compared to estimators previously proposed for identifying lines, namely: (1) minimally biased estimates (G) of favorable dominant alleles present in I _w but not in I ₁ and I ₂; (2) minimum estimate of an upper bound (UBND) on G; and (3) predicted three-way cross (PTC) performance. Based on a set of maize (Zea mays L.) grain yield data, correlations among the four estimators were relatively high, but indicated that rankings of I _w lines vary with the particular estimator used. Rankings of three I _w lines based on the frequency of F₂ test crosses superior to B73×Mo17 were identical to rankings based on NI, but differed from rankings based on G, PTC, and UBND. NI also was the best predictor of the mean of the upper 10% ({ovx}_0.1) of (I ₂×I _w) F₂×I ₁ or (I ₁×I _w) F₂×I ₂ test crosses based on simulated data. Being a simple statistic highly correlated to {ovx}_0.1, NI may be useful in applied breeding programs.A contribution from Lifaco Genetics, a Groupe Limagrain company     

Kinetics of ammonium, nitrate and phosphorus uptake by Canna indica and Schoenoplectus validus

Canna indica L. is an upright perennial rhizomatous herb, and Schoenoplectus validus (Vahl) A. Löve and D. Löve is a tall, perennial, herbaceous sedge. The nutrient uptake kinetics of C. indica and S. validus were investigated using the modified depletion method after plants were grown for 4 weeks in simulated secondary-treated wastewater. The maximum uptake rate (I_max) and Michaelis–Menten constant (K_m) were estimated by iterative curve fitting. The I_max for NH₄N (623 μmol g⁻¹ dry root weight h⁻¹) was significantly higher than that for NO₃N (338 μmol g⁻¹ dry root weight h⁻¹) in S. validus. In contrast, no difference was observed in C. indica. The I_max values for NO₃N and NH₄N were higher in S. validus than in C. indica. A significantly lower K_m was detected for NO₃N uptake in C. indica (385 μmol L⁻¹) compared to that in S. validus (1908 μmol L⁻¹). The I_max for PO₄P did not differ between the plant species. The K_m for PO₄P was significantly higher in C. indica (157 μmol L⁻¹) than in S. validus (60 μmol L⁻¹). In conclusion, we found that S. validus preferred NH₄N over NO₃N, had greater capacity for N uptake and higher affinity for PO₄P, but C. indica had greater affinity for NO₃N. Nutrient uptake capacity is likely related to habitat preference, and is influenced by the structure of roots and rhizomes.     

Effect of Inorganic and Organic Tin Compounds on ACh- and Voltage-Activated Na Currents

1. Inorganic tin and organotin compounds, occurring in aquatic ecosystems, are toxic and can cause behavioral abnormalities in living organisms. To determine the possible neuronal basis of these actions, the effects of both forms of Sn were studied on identified neurones of the mollusk, Lymnaea stagnalis L.2. SnCl₂ caused a dose-dependent decrease in the acetylcholine (Ach)-induced inward current. The effective threshold concentration, measured by a two microelectrode voltage clamp technique, was 0.1 M, and the maximal effect occurred at 5 M SnCl₂. The depression of the inward current was greater after a 10 min preapplication (20%) than after 3 min treatment (7%).3. The next series of experiments compared the actions of inorganic or organic tin compounds. In whole cell clamp experiments both (CH₃)₂SnCl₂ and (CH₃)₃SnCl, like inorganic Sn, decreased the amplitude of Ach-induced current. Increasing the duration of the preapplication time resulted in an increase in the effect, but the action was not reversible. SnCl₂ treatment caused a concentration-dependent alteration (initial potentiation followed by depression) of the amplitude of I _Na(V) over the whole voltage range and slightly shifted the I–V curves to the left. In contrast, trimethyl tin decreased the amplitude of I _Na(V) only at high concentration (100 M). The activation time course of I _Na was increased ( = 0.43 ms in control and 0.55 ms in Sn), but Sn did not alter the inactivation parameters ( = 3.43 and 3.41 ms).4. These results support earlier findings that agonist- and voltage-activated channels are direct targets of toxic metals. We conclude that tin in both inorganic and organic forms acts at neuronal membranes to modulate synaptic transmission through direct actions on agonist-activated ion channels, and suggest that these actions may be the basis of the altered behavior of animals in tin-polluted environments.     

Exopolysaccharide and extracellular metabolite production by Lactobacillus delbrueckii subsp. bulgaricus, grown on lactose in continuous culture

Lactobacillus delbrueckii subsp. bulgaricus NCFB 2483, when grown on lactose in continuous culture, showed increasing specific yields and volumetric productivities of exopolysaccharide (EPS) with increasing dilution rate. Specific and volumetric productivities of lactate and galactose, as extracellular metabolites, increased in response to the incremental changes in the dilution rate up to 0.4 h^–1. Elevated Y_p/s values determined for EPS (0.025 g EPSg lactose^–1) at the dilution rates of 0.3 h^–1–0.4 h^–1, relative to those determined at lower dilution rates, suggest a diversion of carbon flux towards EPS being associated with the higher rates of growth.     

Phosphate-limited growth of Chromatium vinosum in continuous culture

Chromatium vinosum DSM 185 was grown in continuous culture at a constant dilution rate of 0.071 h^-1 with sulfide as the only electron donor. The organism was subjected to conditions ranging from phosphate limitation (S _R-phosphate=2.7 M and S _R-sulfide=1.8 mM) to sulfide limitation (S _R-phosphate=86 M and S _R-sulfide=1.8 mM). At values of S _R-phosphate below 7.5 M the culture was washed out, whereas S _R-phosphate above this value resulted in steady states. The saturation constant (K ) for growth on phosphate was estimated to be between 2.6 and 4.1 M. The specific phosphorus content of the cells increased from 0.30 to 0.85 mol P mg^-1 protein with increasing S _R-phosphate. The specific rate of phosphate uptake increased with increasing S _R-phosphate, and displayed a non-hyperbolic saturation relationship with respect to the concentration of phosphate in the inflowing medium. Approximation of a hyperbolic saturation function yielded a maximum uptake rate (V _max) of 85 nmol P mg^-1 protein h^-1, and a saturation constant for uptake (K _t) of 0.7 M. When phosphate was supplied in excess 8.5% of the phosphate taken up by the cells was excreted as organic phosphorus at a specific rate of 8 nmol P mg^-1 protein h^-1.Non-standard abbreviations BChla bacteriochlorophyll a - D dilution rate; _max, maximum specific growth rate - maximum specific growth rate if the substrate were not inhibitory - K saturation constant for growth on phosphate - V _max maximum rate of phosphate uptake - K _i saturation constant for phosphate uptake - K _i inhibition constant for growth in the presence of sulfide - S _R concentration of substrate in the inflowing medium     

Photosynthetic electron transfer system is inoperative in anaerobic cells of Erythrobacter species strain OCh 114

Some of the photosynthetic reactions were measured under aerobic and anaerobic conditions in intact cells of an aerobic photosynthetic bacterium Erythrobacter species strain OCh 114 (ATCC No. 33942). In intact cells, the flash-light induced oxidation of cytochrome c-551, the continuous light-induced oxidation of reaction center bacteriochlorophyll and the continuous light-induced pH change ( ) of the suspension decreased on aerobic-anaerobic transition and almost disappeared under anaerobic conditions. These photosynthetic reactions reappeared when the suspension was aerated again. These phenomena were reconciled with the fact that Erythrobacter sp. cannot grow anaerobically even in the light. The incompetence of photoanaerobic growth of this bacterium was explained by the reduction of the primary electron acceptor (Q_I) before illumination, resulting partly from the relatively high midpoint potential of Q_I of this bacterium.Abbreviations Q_I Primary electron acceptor - E_h ambient redox potential - E_m midpoint redox potential     

The quantal gating charge of sodium channel inactivation

Using a very low noise voltage clamp technique it has been possible to record from the squid giant axon a slow component of gating current (I _g ) during the inactivation phase of the macroscopic sodium current (I _Na ) which was hitherto buried in the baseline noise. In order to examine whether this slowI _g contains gating charge that originates from transitions between the open (O) and the inactivated (I) states, which would indicate a true voltage dependence of inactivation, or whether other transitions contribute charge to slowI _g , a new model independent analysis termed isochronic plot analysis has been developed. From a direct correlation ofI _g and the time derivative of the sodium conductance dg _Na/d the condition when only O-I transitions occur is detected. Then the ratio of the two signals is constant and a straight line appears in an isochronic plot ofI _g vs. dg _Na/d . Its slope does not depend on voltage or time and corresponds to the quantal gating charge of the O-I transition (q _h ) divided by the single channel ionic conductance (). This condition was found at voltages above – 10 mV up to + 40 mV and a figure of 1.21e ^– was obtained forq _h at temperatures of 5 and 15°C. At lower voltages additional charge from other transitions, e.g. closed to open, is displaced during macroscopic inactivation. This means that conventional Eyring rate analysis of the inactivation time constant _h is only valid above – 10 mV and here the figure forq _h was confirmed also from this analysis. It is further shown that most of the present controversies surrounding the voltage dependence of inactivation can be clarified. The validity of the isochronic plot analysis has been confirmed using simulated gating and ionic currents.Abbreviations I _g gating current - I _Na sodium ionic current - g _Na macroscopic sodium conductance - single channel conductance - C, O, I closed, open, inactivated state occupancy of channels - g _h quantal charge displaced in a single O-I transition of Na channel - e ^– equivalent electron charge - h index referring to inactivation process - S _l limiting slope in isochronic plot see Eq.(3) - fractional distance, see Fig. 4 and (4, 5) - TMA tetramethylammonium - TTX tetrodotoxin - Tris tris(hydroxymethyl)aminomethane - HEPES N-2-hydroxyethylpiperazine-N-2-ethanesulfonic acid     

Preferential Inhibition of I h in Rat Trigeminal Ganglion Neurons by an Organic Blocker

The potency and specificity of a novel organic I _h current blocker DK-AH 268 (DK, Boehringer) was studied in cultured rat trigeminal ganglion neurons using whole-cell patch-clamp recording techniques. In neurons current-clamped at the resting potential, the application of 10 μm DK caused a slight hyperpolarization of the membrane potential and a small increase in the threshold for action potential discharge without any major change in the shape of the action potential. In voltage-clamped neurons, DK caused a reduction of a hyperpolarization-activated current. Current subtraction protocols revealed that the time-dependent, hyperpolarization-activated currents blocked by 10 μm DK or external Cs⁺ (3 mm) had virtually identical activation properties, suggesting that DK and Cs⁺ caused blockade of the same current, namely I _h . The block of I _h by DK was dose-dependent. At the intermediate and higher concentrations of DK (10 and 100 μm) a decrease in specificity was observed so that time-independent, inwardly rectifying and noninactivating, voltage-gated outward potassium currents were also reduced by DK but to a much lesser extent than the time-dependent, hyperpolarization-activated currents. Blockade of the time-dependent, hyperpolarization-activated currents by DK appeared to be use-dependent since it required hyperpolarization for the effect to take place. Relief of DK block was also aided by membrane hyperpolarization. Since both the time-dependent current blocked by DK and the Cs⁺-sensitive time-dependent current behaved as I _h , we conclude that 10 μm DK can preferentially reduce I _h without a major effect on other potassium currents. Thus, DK may be a useful agent in the investigation of the function of I _h in neurons. Received: 3 March 1995/Revised: 8 July 1997     

Inheritance of resistance to potyviruses in Phaseolus vulgaris L. II. Linkage relations and utility of a dominant gene for lethal systemic necrosis to soybean mosaic virus

Summary A single dominant factor, Hss, that conditions a rapid lethal necrotic response to soybean mosaic virus (SMV) has been identified in Phaseolus vulgaris L. cv. Black Turtle Soup, line BT-1. Inoculated plants carrying this factor developed pinpoint necrotic lesions on inoculated tissue followed by systemic vascular necrosis and plant death within about 7 days, regardless of ambient temperature. BT-1 also carries dominant resistance to potyviruses attributed to the tightly linked or identical factors, I, Bcm, Cam, and Hsw, so linkage with Hss was evaluated. No recombinants were identified among 381 F₃ families segregating for potyvirus susceptibility, thus if Hss is a distinct factor, it is tightly linked to I, Bcm, Cam, and Hsw. BT-1 was also crossed reciprocally with the line Great Northern 1140 (GN 1140) in which the dominant gene, Smv, for systemic resistance to SMV was first identified. Smv and Hss segregated independently and are co-dominant. The (GN 1140 x BT-1) F₁ populations showed a seasonal shift of the codominant phenotype. Evaluation of the (GN 1140 x BT-1) F₂ population under conditions where Smv is partially dominant allowed additional phenotypic classes to be distinguished. Pathotype specificity has not been demonstrated for either Smv or Hss. Genotypes that are homozygous for both dominant alleles are systemically resistant to the virus and in addition show undetectable local viral replication or and no seed transmission. This work demonstrates that a gene which conditions a systemic lethal response to a pathogen may be combined with additional gene(s) to create an improved resistant phenotype.     

Ca-sensitive sodium absorption in the colon of Xenopus laevis

Summary Transepithelial electrogenic Na transport (I_Na) was investigated in the colon of the frog Xenopus laevis with electrophysiological methods in vitro. The short circuit current (I_sc) of the voltage-clamped tissue was 24.2±1.8 A·cm^-2 (n=10). About 60% of this current was generated by electrogenic Na transport. Removal of Ca²⁺ from the mucosal Ringer solution stimulated I_Na by about 120%. I_Na was not blockable by amiloride (0.1 mmol·l^-1), a specific Na-channel blocker in epithelia, but a fully and reversible inhibition was achieved by mucosal application of 1 mmol·l^-1 lanthanum (La^3-). No Na-self-inhibition was found, because I_Na increased linearly with the mucosal Na concentration. A stimulation of I_Na by antidiuretic hormones was not possible. The analysis of fluctuations in the short circuit current (noise analysis) indicated that Na ions pass the apical cell membrane via a Ca-sensitive ion channel. The results clearly demonstrate that in the colon of Xenopus laevis Na ions are absorbed through Ca-sensitive apical ion channels. They differ considerably in their properties and regulation from the amiloride-sensitive Na channel which is typically found in the colon of vertebrates.Abbreviations G _T transepithelial conductance - I _sc short circuit current - I _Na transepithelial Na-current - m mucosal - s serosal - PDS power density spectrum - f frequency - f _c corner frequency of the Lorentzian component of the PDS - S(f) power density of the Lorentzian component of the PDS - S_o plateau value of the Lorentzian component of the PDS     

Modeling of the pyruvate production with<Emphasis Type="Italic"> Escherichia coli</Emphasis> in a fed-batch bioreactor

A family of 10 competing, unstructured models has been developed to model cell growth, substrate consumption, and product formation of the pyruvate producing strain Escherichia coli YYC202 ldhA::Kan strain used in fed-batch processes. The strain is completely blocked in its ability to convert pyruvate into acetyl-CoA or acetate (using glucose as the carbon source) resulting in an acetate auxotrophy during growth in glucose minimal medium. Parameter estimation was carried out using data from fed-batch fermentation performed at constant glucose feed rates of q_VG=10 mL h^–1. Acetate was fed according to the previously developed feeding strategy. While the model identification was realized by least-square fit, the model discrimination was based on the model selection criterion (MSC). The validation of model parameters was performed applying data from two different fed-batch experiments with glucose feed rate q_VG=20 and 30 mL h^–1, respectively. Consequently, the most suitable model was identified that reflected the pyruvate and biomass curves adequately by considering a pyruvate inhibited growth (Jerusalimsky approach) and pyruvate inhibited product formation (described by modified Luedeking–Piret/Levenspiel term).List of symbols c_A acetate concentration (g L^–1) - c_A,0 acetate concentration in the feed (g L^–1) - c_G glucose concentration (g L^–1) - c_G,0 glucose concentration in the feed (g L^–1) - c_P pyruvate concentration (g L^–1) - c_P,max critical pyruvate concentration above which reaction cannot proceed (g L^–1) - c_X biomass concentration (g L^–1) - K_I inhibition constant for pyruvate production (g L^–1) - K_I^A inhibition constant for biomass growth on acetate (g L^–1) - K_P saturation constant for pyruvate production (g L^–1) - K_P inhibition constant of Jerusalimsky (g L^–1) - K_S^A Monod growth constant for acetate (g L^–1) - K_S^G Monod growth constant for glucose (g L^–1) - m_A maintenance coefficient for growth on acetate (g g^–1 h^–1) - m_G maintenance coefficient for growth on glucose (g g^–1 h^–1) - n constant of extended Monod kinetics (Levenspiel) (–) - q_V volumetric flow rate (L h^–1) - q_VA volumetric flow rate of acetate (L h^–1) - q_VG volumetric flow rate of glucose (L h^–1) - r_A specific rate of acetate consumption (g g^–1 h^–1) - r_G specific rate of glucose consumption (g g^–1 h^–1) - r_P specific rate of pyruvate production (g g^–1 h^–1) - r_P,max maximum specific rate of pyruvate production (g g^–1 h^–1) - t time (h) - V reaction (broth) volume (L) - Y_P/G yield coefficient pyruvate from glucose (g g^–1) - Y_X/A yield coefficient biomass from acetate (g g^–1) - Y_X/A,max maximum yield coefficient biomass from acetate (g g^–1) - Y_X/G yield coefficient biomass from glucose (g g^–1) - Y_X/G,max maximum yield coefficient biomass from glucose (g g^–1) - growth associated product formation coefficient (g g^–1) - non-growth associated product formation coefficient (g g^–1 h^–1) - specific growth rate (h^–1) - _max maximum specific growth rate (h^–1)     

The inhibitory chloride channel activated by glutamate as well asγ-amino-butyric acid (GABA)

Summary Outside-out and inside-out patches of membrane were excised from different muscles of crayfish (Austropotamobius torrentium) and single channel currents elicited by synaptic transmitters and their analogues were measured with the patchclamp technique. If the Cl^–-concentration was high on both sides of the membrane, glutamate even at concentrations <1 M elicited low amplitude single channel currents, which were identified to be Cl^–-currents. The same channels were also activated by 10 M GABA. Glutamate and GABA showed competition in activating these inhibitory channels. Amplitude histograms of the single channel currents presented well defined peaks corresponding to 3 channel substatesI ₁,I ₂ andI ₃, with conductances of about(I₁)=22 pS in high chloride corresponding to a permeability _Cl(I₁)=3.5× 10^–14 cm³/s),(I₂)=2(I₁) and(I₃)=3(I₁). Glutamate activated preferably stateI ₁, and GABA stateI ₂, but both could activate all states at sufficient concentration. Distributions of the open times in the different states were plotted and could be fitted each with one or two exponentials described by time constants of(I₁) of 1 and 6 ms,(I₂) of 2 to 3 ms, and(I₃) or 1 to 2 ms. The burst durations had components of 3 to 4 and of 30 to 40 ms. All these durations were approximately the same when the channels were activated by glutamate and GABA. The analogue quisqualate of glutamate, as well as the GABA analogue-guanidino propionic acid also elicited the respective patterns of states of the inhibitory channel. Quisqualate is by far the most effective agonist and glutamate is more effective than GABA at the inhibitory receptor. Picrotoxin blocked activation of the inhibitory channel by GABA more effectively than by glutamate. The importance of the activation of the inhibitory channel by glutamate as well as by GABA and their analogues is discussed. Elements of a tentative reaction schema are proposed.     

Modelling continuous culture of Rhodospirillum rubrum in photobioreactor under light limited conditions

Rhodospirillum rubrum was grown continuously and photoheterotrophically under light limitation using a cylindrical photobioreactor in which the steady state biomass concentration was varied between 0.4 to 4 kg m^–3 at a constant radiant incident flux of 100 W m^–2. Kinetic and stoichiometric models for the growth are proposed. The biomass productivities, acetate consumption rate and the CO₂ production rate can be quantitatively predicted to a high level of accuracy by the proposed model calculations. Nomenclature: C _X, biomass concentration (kg m^–3) D, dilution rate (h^–1) Ea, mean mass absorption coefficient (m² kg^–1) I , total available radiant light energy (W m^–2) K, half saturation constant for light (W m^–2) R _W, boundary radius defining the working illuminated volume (m) r _X, local biomass volumetric rate (kg m^–3 h^–1) <r _X>, mean volumetric growth rate (kg m^–3 h^–1) V _W, illuminated working volume in the PBR (m^–3). Greek letters: , working illuminated fraction (–) _M, maximum quantum yield (–) bar, mean energetic yield (kg J^–1).     

Different photoreceptors within the same retina express unique combinations of potassium channels

Single electrode current and voltage clamp recordings in Calliphora, and whole-cell voltage clamp recordings in Drosophila were used to characterise the voltage-gated K channels in both major classes of photoreceptors, R7/8 (long visual fibres, LVFs) and R1-6 (short visual fibres, SVFs). R7/8 were identified by their unique spectral properties, ca. 3–4 fold higher input resistances and 3–4 fold lower cell capacitance. In Calliphora SVFs possess both fast and slow activating delayed rectifier potassium conductances. Drosophila SVFs possess a slowly inactivating delayed rectifier (I_Ks), a very rapidly inactivating A channel encoded by the Shaker gene (I_A), and, in a minority of cells, a third K conductance with intermediate kinetics (I_Kf). In both specs the LVFs lack the slowest component, but exhibit the faster K conductance(s) with properties indistinguishable from those in the SVFs. These findings add to established evidence demonstrating the significant role played by potassium channels in tuning the photoreceptor membrane. The results also suggest that R1-6 photoreceptors and R7/8 form inputs to visual subsystems tuned to different temporal frequencies.Abbreviations LVF long visual fibre - SVF short visual fibre - R1-6 retinular cells 1 to 6 inclusive - R7/8 retinular cell 7 and 8 - I _A rapidly inactivating A type potassium conductance; channel coded by Shaker gene - I _Kf rapidly activating, slowly inactivating delayed rectifier-like potassium conductance - I _Ks slowly activating, slowly inactivating delayed rectifier-like potassium conductance - I _KDs slowly activating delayed rectifier potassium conductance - I _KDf rapidly activating delayed rectifier potassium conductance     

Competition between sulfate-reducing and methanogenic bacteria for H2 under resting and growing conditions

The basis for the outcome of competition between sulfidogens and methanogens for H₂ was examined by comparing the kinetic parameters of representatives of each group separately and in co-culture. Michaelis-Menten parameters (V _max and K _m) for four methanogens and five sulfate-reducing bacteria were determined from H₂-depletion data. Further, Monod growth parameters (_max, K _s, Y _H2) for Desulfovibrio sp. G11 and Methanospirillum hungatei JF-1 were similarly estimated. H₂ K _m values for the methanogenic bacteria ranged from 2.5 M (Methanospirillum PM1) to 13 M for Methanosarcina barkeri MS; Methanospirillum hungatei JF-1 and Methanobacterium PM2 had intermediate H₂ K _m estimates of 5 M. Average H₂ K _m estimates for the five sulfidogens was 1.2 M. No consistent difference among the V _max estimates for the above sulfidogens (mean=100 nmol H₂ min^-1 mg^-1 protein) and methanogens (mean=110 nmol H₂ min^-1 mg^-1 protein) was found. A two-term Michaelis-Menten equation accurately predicted the apparent H₂ K _m values and the fate of H₂ by resting co-cultures of sulfate-reducers and methanogens. Half-saturation coefficients (K _s) for H₂-limited growth of Desulfovibrio sp. G11 (2–4 M) and Methanospirillum JF-1 (6–7 M) were comparable to H₂ K _m estimates obtained for these organisms. Maximum specific growth rates for Desulfovibrio sp. G11 (0.05 h^-1) were similar to those of Methanospirillum JF-1 (0.05–0.06 h^-1); whereas G11 had an average yield coefficient 4 x that of JF-1. Calculated _max and V _max/K _m values for the methanogens and sulfidogens studied predict that the latter bacterial group will process more H₂ whether these organisms are in a growing or resting state, when the H₂ concentration is in the first-order region.