Water influx and efflux in free-flying pigeons

We used tritium-labeled water to measure total body water, water influx (which approximated oxidative water production) and water efflux in free-flying tippler pigeons (Columba livia) during flights that lasted on average 4.2 h. At experimental air temperatures ranging from 18 to 27 °C, mean water efflux by evaporation and excretion [6.3 ± 1.3 (SD) ml · h⁻¹, n = 14] exceeded water influx from oxidative water and inspired air (1.4 ± 0.7 ml · h⁻¹, n = 14), and the birds dehydrated at 4.9 ± 0.9 ml · h⁻¹. This was not significantly different from gravimetrically measured mass loss of 6.2 ± 2.1 g · h⁻¹ (t = 1.902, n = 14, P>0.05). This flight-induced dehydration resulted in an increase in plasma osmolality of 4.3 ± 3.0 mosmol · kg⁻¹ · h⁻¹ during flights of 3–4 h. At 27 °C, the increase in plasma osmolality above pre-flight levels (ΔP _osm = 7.6±4.29 mosmol · kg⁻¹ · h⁻¹, n = 6) was significantly higher than that at 18 °C (ΔP _osm = 0.83±2.23 mosmol · kg⁻¹ · h⁻¹, (t = 3.43, n = 6, P < 0.05). Post-flight haematocrit values were on average 1.1% lower than pre-flight levels, suggesting plasma expansion. Water efflux values during free flight were within 9% of those in the one published field study (Gessaman et al. 1991), and within the range of values for net water loss determined from mass balance during wind tunnel experiments (Biesel and Nachtigall 1987). Our net water loss rates were substantially higher than those estimated by a simulation model (Carmi et al. 1992) suggesting some re-evaluation of the model assumptions is required. Accepted: 8 April 1997     

The use of amiloride to uncouple branchial sodium and proton fluxes in the brown trout, Salmo trutta

Resting proton, ammonium and sodium fluxes in Salmo trutta were 492.6 ± 19.5 (n = 29); 122.9 ± 34.2 (n = 28) and 277.1 ± 18.5 (n = 50) μmol · kg⁻¹ · h⁻¹, respectively. The resting transepithelial potential was found to be composed of three successive potentials, the outermost averaging −7.36 ± 0.19mV, the second, −14.3 ± 1.4 mV and the third −37 ± 1.7 mV. Amiloride inhibits the proton, ammonium and sodium fluxes in a dose-dependent manner at concentrations of 0.5 mmol · 1⁻¹ and 0.1 mmol · l⁻¹, but at 0.01 mmol · l⁻¹, proton and ammonium fluxes remained at control levels whilst the sodium was reduced to 70.59 ± 7.29 μmol · kg⁻¹ · h⁻¹. The trans-epithelial potential was effected in a bi-phasic manner by 0.5 mmol · l⁻¹ amiloride. An initial hyperpolarisation of ca. 6 mV was followed by a sustained depolarisation of ca. 14 mV (towards zero) which persisted until the amiloride was washed off the gill. The initial hyperpolarisation was thought to reflect a rapid inhibition of a positive inward sodium current and the subsequent depolarisation was due to the inhibition of a positive outward current (proton) which would abolish the transepithelial potential. However, at 0.01 mmol ·  l⁻¹ only the hyperpolarisation was seen, due to the inhibition of only the inward sodium current. Acetazolamide (0.1 mmol · l⁻¹) was found to have no significant effect on the proton, ammonium and sodium fluxes. These results indicate that the proton and sodium fluxes across the gill of the freshwater trout are not tightly linked. While this suggests that the trout gill resembles the model of Ehrenburg et al. (1985) of sodium uptake in frog skin, the apical potentials measured in the pavement epithelial cell(s) are too low to account for sodium uptake unless the activity of the sodium in the cells is very low. Accepted: 8 August 1996     

Water and sodium balances and metabolic physiology of house mice (Mus domesticus) and short-tailed mice (Leggadina lakedownensis) under laboratory conditions

A laboratory study investigated the metabolic physiology, and response to variable periods of water and sodium supply, of two arid-zone rodents, the house mouse (Mus domesticus) and the Lakeland Downs short-tailed mouse (Leggadina lakedownensis) under controlled conditions. Fractional water fluxes for M. domesticus (24 ± 0.8%) were significantly higher than those of L. lakedownensis (17 ± 0.7%) when provided with food ad libitum. In addition, the amount of water produced by M. domesticus and by L. lakedownensis from metabolic processes (1.3 ± 0.4 ml · day⁻¹ and 1.2 ± 0.4 ml · day⁻¹, respectively) was insufficient to provide them with their minimum water requirement (1.4 ± 0.2 ml · day⁻¹ and 2.0 ± 0.3 ml · day⁻¹, respectively). For both species of rodent, evaporative water loss was lowest at 25 °C, but remained significantly higher in M. domesticus (1.1 ± 0.1 mg H₂O · g^−0.122 · h⁻¹) than in L. lakedownensis (0.6 ± 0.1 mg H₂O · g^−0.122 · h⁻¹). When deprived of drinking water, mice of both species initially lost body mass, but regained it within 18 days following an increase in the amount of seed consumed. Both species were capable of drinking water of variable saline concentrations up to 1 mol · l⁻¹, and compensated for the increased sodium in the water by excreting more urine to remove the sodium. Basal metabolic rate was significantly higher in M. domesticus (3.3 ± 0.2 mg O₂ · g^−0.75 · h⁻¹) than in L. lakedownensis (2.5 ± 0.1 mg O₂ · g^−0.75 · h⁻¹). The study provides good evidence that water flux differences between M. domesticus and L. lakedownensis in the field are due to a requirement for more water in M. domesticus to meet their physiological and metabolic demands. Sodium fluxes were lower than those observed in free-ranging mice, whose relatively high sodium fluxes may reflect sodium associated with available food. Accepted: 16 August 1999     

Effect of manipulation of the renin-angiotensin system in control of drinking in juvenile Atlantic salmon (Salmosalar L) in fresh water and after transfer to sea water

Drinking in Atlantic salmon (Salmo salar) juveniles was investigated in fresh water and following transfer to sea water. There was a significant effect of fish size on drinking, and smolts (20–30 g) imbibed about ten times less water than alevins of 0.2–0.3 g. Freshwater smolts drank at a rate of 0.15 ± 0.03 ml · kg⁻¹ · h⁻¹ and administration of doses of 10 or 20 mg · kg⁻¹ of papaverine (stimulator of the renin- angiotensin system RAS) or [Asn¹, Val⁵]-Angiotensin II (0.4 μmol · kg⁻¹) resulted in significant increases in drinking, while administration of the angiotensin converting enzyme inhibitor, enalapril (50 mg · kg⁻¹) had no effect on drinking. Transfer of Atlantic salmon smolts to 1/3, 2/3 and full strength sea water resulted in significant increases in drinking to 1.06 ± 0.12, 1.24 ± 0.0.16 and 3.89 ± 0.28 ml · kg⁻¹ · h⁻¹, respectively. In sea water, stimulation of the endogenous RAS by administration of papaverine (20 mg · kg⁻¹) resulted in a 20% increase in drinking, while administration of enalapril to doses of 50 and 200 mg · kg⁻¹ lowered drinking to 1.99 ± 0.48 and 0.32 ± 0.06 ml · kg⁻¹ · h⁻¹, respectively. All treatments were without effect on blood plasma levels of Na⁺ and Cl⁻ in fresh water, while in sea water smolts both stimulation and inhibition of drinking resulted in hemoconcentration of Na⁺ and Cl⁻. The role of the renin angiotensin system in control of drinking and hydromineral balance in Atlantic salmon is discussed. Accepted: 27 February 1997     

Catecholamine release in heat-stressed Antarctic fish causes proton extrusion by the red cells

Two species of Antarctic fish were stressed by moving them from seawater at −1 °C to seawater at 10 °C and holding them for a period of 10 min. The active cryopelagic species Pagothenia borchgrevinki maintained heart rate while in the benthic species Trematomus bernacchii there was an increase in heart rate. Blood pressure did not change in either species. Both species released catecholamines into the circulation as a consequence of the stress. P. borchgrevinki released the greater amounts, having mean plasma concentrations of 177 ± 54 nmol · l⁻¹ noradrenaline and 263 ± 131 nmol · l⁻¹ adrenaline at 10 min. Plasma noradrenaline concentrations rose to 47 ± 14 nmol · l⁻¹ and adrenaline to 73 ± 28 nmol · l⁻¹ in T. bernacchii. Blood from P. borchgrevinki was tonometered in the presence of isoprenaline. A fall in extracellular pH suggests the presence of a Na⁺/H⁺ antiporter on the red cell membrane, the first demonstration of this in an Antarctic fish. Treatment with the β-adrenergic antagonist drug sotalol inhibited swelling of red blood cells taken from temperature-stressed P. borchgrevinki, suggesting that the antiporter responds to endogenous catecholamines. Accepted: 22 January 1998     

Steady-state kinetics, micellar effects, and the mechanism of peroxidase-catalyzed oxidation of n -alkylferrocenes by hydrogen peroxide

 Kinetics of the steady-state oxidation of n–alkylferrocenes (alkyl = H, Me, Et, Bu and C₅H₁₁) by H₂O₂ to form the corresponding ferricenium cations catalyzed by horseradish peroxidase has been studied in micellar systems of Triton X-100, CTAB, and SDS, mostly at pH 6.0 and 25  °C. The rate of oxidation of ferrocenes with longer alkyl radicals is too slow to be measured. The reaction obeying the [RFc]:[H₂O₂] = 2 : 1 stoichiometry is strictly first-order in both HRP and RFc in a wide concentration range. The corresponding observed second-order rate constants k, which refer to the interaction of the peroxidase compound II (HRP-II) with RFc, decrease with the elongation of the alkyl substituent R, and this in turn is accompanied by an increase in the formal redox potentials E°′ in the same medium. Increasing the surfactant concentration lowers the rate constants k, the effect being due to the nonproductive binding of RFc to micelles rather than to enzyme inactivation. The micellar effects are accounted for in terms of the Berezin pseudo-phase model of micellar catalysis applied to the interaction of enzyme with organometallic substrates. The oxidation was found to occur primarily in the aqueous pseudo-phase and the calculated intrinsic second-order rate constants k _w are (1.9 ± 0.5)×10⁵, (2.7 ± 0.1)×10⁴, and (5.9 ± 0.6)×10³ M^–1 s^–1 for HFc, EtFc, and n–BuFc, respectively. The data obtained were used for estimating the self-exchange rate constants for the HRP-II/HRP couple in terms of the Marcus formalism. Received: 15 July 1996 / Accepted: 15 November 1996     

Optical fractionation of chlorophyll and primary production for coastal waters of the Southern Ocean

Our objective was to quantify the potential variability in remotely sensed chlorophyll a (Chl a) and primary productivity in coastal waters of the Southern Ocean. From data collected throughout the springs/summers of 1991–1994, we calculated the proportion of water column Chl a and primary productivity within the upper optical attenuation length (K ⁻¹ _par) and the satellite-weighted depth. The temporal variability was resolved every 2–3 days and was observed to be greater within years than between years. Three-year averages (n=223) revealed that 10.2 ± 3.6% of total Chl a and 14.8 ± 6.5% of production occurred within satellite-weighted depth in predominantly Case I waters. The average values were twice as high within K ⁻¹ _par, 24.1 ± 8% of total Chl a and 34 ± 9% of production respectively. Masked in these long-term averages are very large changes occurring on short time scales of seasonal blooms. We observed that the patterns of Chl a vertical distribution within blooms are also subject to taxonomic influence and dependent upon the physiological state of the phytoplankton. Highest proportions of water column Chl a in the first optical depth were measured during the rapid onset of surface cryptophyte blooms each year, i.e. 50% within K ⁻¹ _par and 30% above the satellite-weighted depth. Lowest fractions, 6% and 2% of biomass within K ⁻¹ _par and satellite-weighted depth respectively, were associated with peak bloom conditions independent of taxonomy. Our analyses suggest that satellite-dependent models of Chl a and subsequent chlorophyll-dependent primary production will be challenging to develop for the near-shore Southern Ocean, especially given the potentially high natural variability in the vertical distribution of Chl a driven by physical forcing, the photoadaptive abilities of polar phytoplankton, and taxonomic influences. Accepted: 27 August 1999     

Gas exchange and heart rate in the harbour porpoise, Phocoena phocoena

The respiratory physiology, heart rates and metabolic rates of two captive juvenile male harbour porpoises (both 28 kg) were measured using a rapid-response respiratory gas analysis system in the laboratory. Breath-hold durations in the laboratory (12 ± 0.3 s, mean ± SEM) were shorter than field observations, although a few breath-holds of over 40 s were recorded. The mean percentage time spent submerged was 89 ± 0.4%. Relative to similarly-sized terrestrial mammals, the respiratory frequency was low (4.9 ± 0.19 breaths · min⁻¹) but with high tidal volumes (1.1 ± 0.01 l), enabling a comparatively high minute rate of gas exchange. Oxygen consumption under these experimental conditions (247 ± 13.8 ml O₂ · min⁻¹) was 1.9-fold higher than predicted by standard scaling relations. These data together with an estimate of the total oxygen stores predicted an aerobic dive limit of 5.4 min. The peak end-tidal O₂ values were related to the length of the previous breath-hold, demonstrating the increased oxygen uptake from the lung for the longer dives. Blood oxygen capacity was 23.5 ± 1.0 ml · 100 ml⁻¹, and the oxygen affinity was high, enabling rapid oxygen loading during ventilation. Accepted: 11 August 1999     

Effects of hypercapnia on blood-gas and acid-base status in the white sturgeon, Acipenser transmontanus

The effect of environmental hypercapnia on respiratory and acid-base variables was studied in white sturgeon, Acipenser transmontanus. Blood PCO₂, PO₂, pH, hemoglobin concentration, and plasma lactate, glucose, catecholamines and cortisol were measured first under normocapnia (water PCO₂ < 0.5 Torr, 1 Torr = 133.32 Pa), then under hypercapnia (25–35 Torr) and a final return to normocapnia at 19 ± 0.5 °C. Acute (≤ 2h) hypercapnia significantly increased arterial PCO₂ (8-fold increase), ventilation frequency (2-fold increase), plasma HCO₃ ⁻ (2.3-fold) and decreased arterial pH (to 7.15 ± 0.02). After 24 h, norepinephrine, epinephrine and cortisol, were significantly increased, and arterial pH reached its nadir (7.10 ± 0.03). During the 72- and 96-h-periods, arterial PCO₂ (24 ± 4.4 Torr) and ventilatory frequency (105 ± 5 breaths min⁻¹) stabilized, HCO₃ ⁻ reached its apparent maximum (23.6 ± 0.0 mmol⁻¹), glucose decreased by 32%, and pH increased significantly to 7.31 + 0.03. The return to normocapnia completely restored arterial PCO₂ (2.5 ± 0.14 Torr), HCO₃ ⁻ (7.4 ± 0.59 mmol · l⁻¹), ventilation frequency (71 ± 7 breaths · min⁻¹), and pH (7.75 ± 0.04). Overall, hypercapnia produced a respiratory acidosis, hyperventilation, a transient norepinephrine “spike”, and increased plasma catecholamines, cortisol, and arterial PO₂. The respiratory acidosis was only partially compensated (35% pH restoration) 96 h after the onset of hypercapnia and resulted in a significantly decreased blood-O₂ affinity (Bohr effect), as determined by construction of in vitro blood O₂ equilibrium curves at 15 °C and 20 °C. Prolonged exposure to hypercapnia may lead to acid-base disturbances and negatively affect growth of white sturgeon. Accepted: 17 August 1997     

Placental Alpha Hemoglobin Stabilizing Protein (AHSP) and recurrent miscarriage

AHSP inhibits cellular production of the reactive oxygen species. Reduced AHSP indicates reduced protection against oxidative stressors. Our objective was to investigate AHSP levels in recurrent miscarriage (RM). Trophoblast was collected from women of 10 weeks gestation: voluntary abortion controls (VA, n = 10); spontaneous first miscarriage with subsequent normal pregnancy (SMSN, n = 15) or with subsequent miscarriage (SMSM, n = 5); RM previously investigated (RMPS, n = 5) or not previously investigated (RM, n = 5). AHSP mRNA and protein were determined using real-time quantitative polymerase chain reaction (PCR) and Western blot, respectively. One-way ANOVA was performed to assess statistical significance (p < 0.05). ahsp mRNA levels were maximally reduced in RM and RMPS (8.0 × 10⁻⁶ ± 1.3 and 8.1 × 10⁻⁶ ± 0.7, respectively) compared with SMSN and VA (16.1 × 10⁻⁶ ± 2.3 and 26.1 × 10⁻⁶ ± 2.7, respectively). SMSM showed levels significantly reduced as well (9.0 × 10⁻⁶ ± 2.3). In RM, a reduced defense from oxidative stressors is evident at first miscarriage, identifying women at high risk for subsequent eventful pregnancy. Reduced AHSP may identify women at risk of experiencing further miscarriages. Monica Emanuelli and Monia Cecati contributed equally to this paper.     

Zinc,Manganese, Calcium,Copper, and Cadmium Level in Scalp Hair Samples of Schizophrenic Patients

The purpose of the study was to determine the concentration of trace elements present in scalp hair sample of schizophrenic patients and to find out the relationship between trace elements level and nutritional status or socioeconomic factors. The study was conducted among 30 schizophrenic male patients and 30 healthy male volunteers. Patients were recruited from Bangabandhu Sheikh Mujib Medical University by random sampling. Hair trace element concentrations were determined by flame atomic absorption spectroscopy and analyzed by independent t test, Pearson’s correlation analysis, regression analysis, and analysis of variance (ANOVA). Mn, Zn, Ca, Cu, and Cd concentrations of schizophrenic patients were 3.8 ± 2.31 μg/gm, 171.6 ± 59.04 μg/gm, 396.23 ± 157.83 μg/gm, 15.40 ± 5.68 μg/gm, and 1.14 ± 0.89 μg/gm of hair sample, while those of control subjects were 4.4 ± 2.32 μg/gm, 199.16 ± 27.85 μg/gm, 620.9 ± 181.55 μg/gm, 12.23 ± 4.56 μg/gm, and 0.47 ± 0.32 μg/gm of hair sample, respectively. The hair concentration of Zn and Ca decreased significantly (p = 0.024; p = 0.000, respectively) and the concentration of Cu and Cd increased significantly (p = 0.021; p = 0.000, respectively) in schizophrenic patients while the concentration of Mn (p = 0.321) remain unchanged. Socioeconomic data reveals that most of the patients were poor, middle-aged and divorced. Mean body mass indices (BMIs) of the control group (22.26 ± 1.91 kg/m²) and the patient group (20.42 ± 3.16 kg/m²) were within the normal range (18.5−25.0 kg/m²). Pearson’s correlation analysis suggested that only Ca concentration of patients had a significant positive correlation with the BMI (r = 0.597; p = 0.000) which was further justified from the regression analysis (R ² = 44%; t = 3.59; p = 0.002) and one-way ANOVA test (F = 3.62; p = 0.015). A significant decrease in the hair concentration of Zn and Ca as well as a significant increase in the hair concentration of Cu and Cd in schizophrenic patients than that of its control group was observed which may provide prognostic tool for the diagnosis and treatment of this disease. However, further work with larger population is suggested to examine the exact correlation between trace element level and the degree of disorder.     

Summer seawater tolerance of small-sized Arctic charr, Salvelinus alpinus, on Svalbard

Migrating Arctic charr (Salvelinus alpinus) parr (118 ± 34.4 mm) were caught close to the rivermouth of the Dieset river on Spitsbergen (79°10′N), Svalbard. When subjected to a seawater tolerance test (34 ppt at 6°C) their blood plasma osmolality and sodium and magnesium concentrations increased significantly. After 90 h of exposure, average plasma osmolality was 410 (±54.1) mOsmol. Corresponding sodium and magnesium concentrations were 207 (±35.9) mmol l⁻¹ and 2.7 (±1.36) mmol l⁻¹, respectively. Survival at this time was only 12.5%. When smaller fish (96 ± 26.6 mm) were exposed to seawater, mortality was 100% within 72 h. We conclude that small-sized Svalbard charr may survive only short periods in seawater. Therefore, the lack of adequate hypoosmoregulatory capacity limits their access to marine food resources. Received: 29 December 1997 / Accepted: 12 April 1998     

Comparative Analysis of Serum Manganese,Zinc, Calcium,Copper and Magnesium Level in Panic Disorder Patients

The purpose of the study was to determine the serum concentration of trace elements of panic disorder patients and to find out the relationship between trace element levels and nutritional status or socio-economic factors. The study was conducted among 54 panic disorder patients and 52 healthy volunteers. Patients were recruited from Bangabandhu Sheikh Mujib Medical University by random sampling. Serum trace element concentrations were determined by flame atomic absorption spectroscopy (for Mg, Zn, Ca, and Cu) as well as graphite furnace (for Mn). Data were analyzed by independent t test, Pearson’s correlation analysis, regression analysis, and ANOVA. The serum concentration of Mn, Zn, Ca, Cu, and Mg in panic disorder patients were 0.37 ± 0.30, 0.67 ± 0.20, 99.91 ± 15.15, 0.83 ± 0.23, and 21.14 ± 3.72 mg/L, while those were 0.4163 ± 0.2527, 0.86 ± 0.3, 106.6073 ± 18.6531, 0.8514 ± 0.3646, and 21.37 ± 2.03 mg/L in control subjects, respectively. The serum concentration of Zn decreased significantly (p = 0.001) in patient group. But the differences of the concentration of Mn, Ca, Cu, and Mg between patient and control group were not significant (p = 0.522, p = 0.065, p = 0.800, and p = 0.712, respectively). Socio-economic data reveal that most of the patients were very poor and middle aged. Mean BMIs of the control group (23.74 ± 2.71 kg/m²) and the patient group (22.62 ± 3.74 kg/m²) were within the normal range (18.5–25.0 kg/m²). There was no significant relationship between serum zinc level and BMI of patients (r = 0.038; p = 0.809). So the decreased level of serum zinc in panic disorder patients was not because of other reasons, but rather it may provide a prognostic tool for the diagnosis and treatment of this disease.     

Milk composition and lactational output in the greater spear-nosed bat, Phyllostomus hastatus

Growth rates of mammalian young are closely linked to the ability of the mother to provide nutrients; thus, milk composition and yield provide a direct measure of maternal investment during lactation in many mammals. We studied changes in milk composition and output throughout lactation in a free-ranging population of the omnivorous bat, Phyllostomus hastatus. Fat and dry matter of milk increased from 9 to 21% and from 21 to 35% of wet mass, respectively, throughout lactation. Energy increased from 6 to 9 kJ · g⁻¹ wet mass, primarily due to the increase in fat concentration. Total sugar levels decreased slightly but non-significantly. Mean sugar level was 4.0% of wet mass. Protein concentration increased from 6 to 11% of wet mass at peak lactation and then decreased as pups approached weaning age. Total milk energy output until pups began to forage was 3609 kJ. Milk levels of Mg, Fe, Ca, K, and Na averaged 0.55 ± 0.26, 0.23 ± 0.2, 8.75 ± 4.17, 5.42 ± 2.11, and 9.87 ± 4.3 mg · g⁻¹ dry matter, respectively. Of the minerals studied, calcium appears to be most limiting in this species. The high degree of variability in foraging time, milk composition and milk yield between individuals at the same stage of lactation could potentially yield high variance in reproductive success among females of this polygynous species. Accepted: 23 January 1997     

A neutral carrier-based liquid membrane microelectrode for divalent putrescine cations

A new ion-selective liquid membrane microelectrode, based on the neutral carrier 1,1′-bis(2,3-naphtho-18-crown-6), is described that shows the dependence of EMF on the activity of divalent putrescine cations a _Put, with the linear slope s _Put = 26 ± 3 mV/decade (mean ± SD, N = 18), in the range 10⁻⁴–10⁻¹ M at 25 ± 1 °C. Values of potentiometric putrescine cation selectivity coefficients of logK ^Pot _{Put j} (mean ± SD, N) are obtained by the separate solution method for the ions K⁺ (1.0 ± 0.4, 10), Na⁺ (−1.2 ± 0.4, 8), Ca²⁺ (−2.3 ± 0.5, 10) and Mg²⁺ (−2.5 ± 0.5, 7). The microelectrode can be applied for the direct analysis of the activities of free divalent putrescine cations in the range 5 × 10⁻⁴ to 10⁻¹ M in an extracellular ionic environment. Established analytical methods, e.g. high performance liquid chromatography, determine the total concentration of the derivatives of free and bound putrescine. Received: 20 December 1998 / Revised version: 7 May 1999 / Accepted: 27 May 1999     

RNA turnover and protein synthesis in fish cells

Protein synthesis in fish has been previously correlated with RNA content. The present study investigates whether protein and RNA synthesis rates are similarly related. Protein and RNA synthesis rates were determined from ³H-phenylalanine and ³H-uridine incorporation, respectively, and expressed as % · day⁻¹ and half-lives, respectively. Three fibroblast cell lines were used: BF-2, RTP, CHSE 214, which are derived from the bluegill, rainbow trout and Chinook salmon, respectively. These cells contained similar RNA concentrations (∼175 μg RNA · mg⁻¹ cell protein). Therefore differences in protein synthesis rates, BF-2 (31.3 ± 1.8)>RTP (25.1 ± 1.7)>CHSE 214 (17.6 ± 1.1), were attributable to RNA translational efficiency. The most translationally efficient RNA (BF-2 cells), 1.8 mg protein synthesised · μg⁻¹ RNA · day⁻¹, corresponded to the lowest RNA half-life, 75.4 ± 6.4 h. Translationally efficient RNA was also energetically efficient with BF-2 cells exploiting the least costly route of nucleotide supply (i.e. exogenous salvage) 3.5–6.0 times more than the least translationally efficient RNA (CHSE 214 cells). These data suggest that differential nucleotide supply, between intracellular synthesis and exogenous salvage, constitutes the area of pre-translational flexibility exploited to maintain RNA synthesis as a fixed energetic cost component of protein synthesis. Accepted: 12 November 1999     

Field energetics and the estimation of pollen and nectar intake in the marsupial honey possum, Tarsipes rostratus, in heathland habitats of South-Western Australia

A method is described, based on the simultaneous turnover of both stable (¹⁸O) and radioactive isotopes (³H and ²²Na), whereby the daily nectar and pollen intake of free-ranging marsupial honey possums (Tarsipes rostratus) may be estimated. The field metabolic rate is measured using doubly labelled water and nectar intake is estimated independently from the measured water and sodium fluxes. The method assumes that free-water intake is negligible (but may be accounted for if not the case), that virtually all dietary sodium is derived from nectar rather than from pollen, and that the animals are in energetic balance over the period of measurement. These assumptions have been tested and found to be robust, except during periods of heavy rain when significant intakes of free-water were recorded. Leaching experiments with pollen grains suggest that less than 10% of the sodium ingested by honey possums is derived from pollen and calculations thus assumed a 90%:10% split between nectar and pollen. Nectar intake averaged 5.9 ± 0.6 ml · day⁻¹ and regressing nectar intake on daily change in body mass predicts an intake of approximately 7 ml · day⁻¹ nectar to maintain balance for a 9 g honey possum. Estimates of pollen intake averaged 660 ± 156 mg · day⁻¹ and a similar regression analysis of the data predicts that a daily intake of approximately 1 g pollen would be needed to maintain mass balance of honey possums. Estimated nectar and pollen intakes did not differ significantly between males and females, but nectar intake was higher in winter compared with dry periods of the year. The sugar content of nectar falls during winter, however, and the overall energy derived from nectar thus remains roughly constant. Estimates of pollen and nectar intake for individual animals were not significantly correlated, suggesting that honey possums forage selectively for these two food items. Accepted: 19 August 1999     

The function of water channels in Chara: The temperature dependence of water and solute flows provides evidence for composite membrane transport and for a slippage of small organic solutes across water channels

Using the cell pressure probe, the effects of temperature on hydraulic conductivity (Lp; osmotic water permeability), solute permeability (permeability coefficient, P_s), and reflection coefficients (σ_s) were measured on internodes of Chara corallina, Klein ex Willd., em R.D.W.. For the first time, complete sets of transport coefficients were obtained in the range between 10 and 35 °C which provided evidence about pathways of water and solutes as they move across the plasma membrane (water channel and bilayer arrays). Test solutes used to check for the selectivity of water channels were monohydric alcohols of different molecular size and shape (ethanol, n-propanol, iso-propanol, and tert-butanol) and heavy water (HDO). Within the limits of accuracy, Q₁₀ values for Lp and for the diffusive water permeability (P_d) were identical (Q₁₀ for Lp = 1.29 ± 0.17 (± SD; n = 15 cells) and Q₁₀ for P_d = 1.25 ± 0.16 (n = 5 cells)). The Q₁₀ values were equivalent to activation energies of E_a = 16.8 ± 6.4 and 16.6 ± 10.0 kJ · mol⁻¹, respectively, which is similar to that of self-diffusion or of viscous flow of water. The Q₁₀ values and activation energies for P_s of the alcohols were significantly larger (ethanol: Q₁₀ = 1.68 ± 0.16, E_a = 37.1 ± 5.9 kJ · mol⁻¹; n-propanol: Q₁₀ =  1.75 ± 0.40, E_a = 43.1 ± 15.3 kJ · mol⁻¹; iso-propanol: Q₁₀ = 2.12 ± 0.42, E_a =  52.2 ± 14.6 kJ · mol⁻¹; tert-butanol: Q₁₀ = 2.13 ± 0.56, E_a = 51.6 ± 17.1 kJ · mol⁻¹; ±SD; n = 5 to 6 cells). Effects of temperature on reflection coefficients were most pronounced. With increasing temperature, σ_s values of the alcohols decreased and those of HDO increased. The data indicate that water and solutes use different pathways when crossing the membrane. Ordinary and isotopic water use water channels and the other test solutes use the bilayer array (composite transport model of membrane). Changes in σ_s values with temperature were found to be a sensitive measure for the open/closed state of water channels. The decrease of σ_s with temperature was theoretically predicted from the temperature dependence of P_s and Lp. Differences between predicted and measured values of σ_s allowed estimation of the bypass flow (slippage) of solutes through water channels which did not completely exclude test solutes. The permeability of channels depended on the structure and size of test solutes. It is concluded that water channels are much less selective than is usually thought. Since water channels represent single-file or no-pass pores, solutes drag along considerable amounts of water as they diffuse across channels. This results in low overall values of σ_s. The σ_s of HDO was extremely low. Its response to temperature was opposite to that for the σ_s of the alcohols. This suggested a stronger effect of temperature on the hydraulic (osmotic) than on the diffusive water flow across individual water channels, i.e. a differential sensitivity of different mechanisms to temperature. Received: 10 October 1996 / Accepted: 2 December 1996     

Metabolic rates in an anadromous clupeid, the American shad (Alosa sapidissima)

To assess the energetics of migration in an anadromous fish, adult American shad (Alosa sapidissima) were swum in a large respirometer at a range of speeds (1.0–2.3 body lengths (BL) s⁻¹, 13–24 °C). Metabolic rate (M_O2) was logarithmically related to swimming speed (Bl s⁻¹; r ² = 0.41, slope = 0.23 ± 0.037) and tailbeat frequency (beats × min⁻¹; r ² = 0.52, slope = 0.003 ± 0.0003). Temperature had a significant effect on metabolic rate (r ² = 0.41) with a Q₁₀ of 2.2. Standard metabolic rate (SMR), determined directly after immobilization with the neuroblocker gallamine triethiodide, ranged from 2.2–6.2 mmolO₂ kg⁻¹ h⁻¹ and scaled with mass (W) such that SMR = 4.0 (±0.03)W^{0.695(±0.15)}. Comparison of directly determined and extrapolated SMR suggests that swimming respirometry provides a good estimate of SMR in this species, given the differences in basal activity monitored by the two methods. Overall, American shad metabolic rates (M_O2 and SMR) were intermediate between salmonids and fast-swimming perciforms, including tunas, and may be a result of evolutionary adaptation to their active pelagic, schooling life history. This study demonstrates variability in metabolic strategy among anadromous fishes that may be important to understanding the relative success of different migratory species under varying environmental conditions. Accepted: 3 March 1999     

Equilibrium dialysis study and mechanistic implications of coenzyme A binding to acetyl-CoA synthase/carbon monoxide dehydrogenase from Clostridium thermoaceticum

Clostridium thermoaceticum were determined by equilibrium dialysis. CoA bound to as-isolated native α ₂ β ₂ enzyme with K _D = 10 ± 8 μM and n = 0.2 ± 0.1 moles per αβ dimer, where K _D is the thermodynamic dissociation constant and n is the number of CoAs bound per αβ dimer of the enzyme. The enzyme is heterogeneous; for example, only  ∼ 30% of α subunits contain A-clusters with labile Ni ions (the remainder have nonlabile Ni ions and are nonfunctional). The observed n value suggests that CoA binds only to αβ units with Ni-labile A-clusters. The CoA binding properties of enzyme lacking labile Ni was essentially the same, indicating that CoA does not bind directly to the Ni of the A-cluster. This was further evidenced by the observation that bound CoA did not inhibit removal of the labile Ni by 1,10-phenanthroline. CoA did not bind CO-reduced enzyme, and the EPR signal exhibited by the one-electron reduced and CO-bound form of the A-cluster was unaffected by the presence of up to 200 μM CoA. In contrast, CoA did bind Ti(III)-citrate-reduced enzyme (K _D = 36 ± 16 μM, n = 0.16 ± 0.08). Implications of these results for the mechanism of catalysis are discussed. Received: 29 March 1999 / Accepted: 8 September 1999