bluuebunny/crossref_metadata_2025_split huggingface dataset:
Calcium-Dependent Action Potentials in Giant Salivary Gland Cells of the LeechHaementeria Ghilianii: Calcium Removal Induces Dependence on Sodium
Authors: Wuttke Werner A. , Berry Michael S. 
Published: April 2021

ABSTRACTAn electrophysiological study was made of the giant, non-coupled salivary gland cells of the leech Haementeria ghilianii (de Filippi, 1849). Resting membrane potential (−40 mV to −80 mV) was primarily dependent on K+, with a small contribution from a Na+ conductance and an electrogenic Na+ pump. Resting Cl− permeability was low. The cells generated overshooting action potentials (70-110 mV, 100-400 ms) which appeared to be mediated exclusively by Ca2+ because they were unaffected by removal of external Na+ and were blocked by 5 mmol 1−1 Co2+. Removal of external Ca2+ and addition of 1 mmol 1−1 EGTA produced spontaneous action potentials of reduced amplitude (peaking at about OmV) and greatly increased duration [typically tens of seconds but sometimes resulting in sustained depolarizations (plateau potentials) extending up to 30min or more]. Action potential amplitude was then dependent on external Na+ concentration, and action potentials were abolished by removal of Na+. The responses were blocked by 5 mmol 1−1 Co2+, indicating that they were produced by Na+ flowing through Ca2+ channels. Addition of micromolar concentrations of Ca2+ to Ca2+-free saline de-creased spike duration and amplitude, suggesting a competition between Na+ and Ca2+. An electrogenic Na+ pump was activated by removal of Ca2+, presumably as a result of the influx of Na+ during spiking; this produced large increases in membrane potential which occurred spontaneously or when Ca2+ was reintro-duced. In normal saline, spike overshoot and duration were increased when the temperature was lowered by 10°C, whereas in Ca2+-free solution, they were reduced by this change. This suggests that the Ca2+ channel may be differentially affected by cooling, depending on the presence or absence of Ca2+
Exercising with and Without Lungs: I. The Effects of Metabolic Cost, Maximal Oxygen Transport and Body Size on Terrestrial Locomotion in Salamander Species
Authors: Full Robert J. , Anderson Bruce D. , Finnerty Casey M. , Feder Martin E. 
Published: April 2021

ABSTRACTMetabolic cost, oxygen consumption , respiratory structure and body size interact to determine the capacity of salamanders for terrestrial locomotion. Salamanders respiring via both lungs and skin, Ambystoma laterale and A. tigrinum, or with skin alone, Desmognathus ochrophaeus and D. quadramaculatus, attained a steady-state , during exercise in a treadmill respirometer. Endurance was correlated with the speed at which maximal was attained Low aerobic costs of transport (60-80% lower than reptiles of similar mass) increased . However, in lungless salamanders a low maximum , decreased significantly. increased only 1·6-to 3·0-fold above resting rates in active lungless salamanders, whereas it could increase 3·5- to 7·0-fold in active lunged salamanders. Lungless salamanders attained maximal at half to one-tenth the speed of lunged animals. Lungless salamanders fatigued in 20 min or less at speeds that lunged salamanders could sustain for 1-2 h. Body size also affected the capacity for oxygen uptake during activity and locomotor performance. The large lungless salamander D. quadramaculatus attained maximum , even at its lowest rate of travel. Cutaneous gas exchange does not provide lungless salamanders with gas transport capacities found in lunged animals. However, only small increases in , may be required for modest levels of activity.
Exercising With and Without Lungs: II. Experimental Elimination of Pulmonary and Buccopharyngeal Gas Exchange in Individual Salamanders (Ambystoma Tigrinum)
Authors: Feder Martin E. 
Published: April 2021

ABSTRACTTo ascertain whether the presence of lungs per se, or some other physiological feature, might account for the differences in oxygen consumption and stamina previously observed in an interspecific comparison (Full et al. 1988), individual salamanders (Ambystoma tigrinum) were exercised on a treadmill before and after their nares and mouth had been sealed. After airway closure, animals behaved normally and suffered no mortality. Airway closure reduced the routine (rate of oxygen consumption) by an average of 47% in six of seven individuals. Animals with open airways increased their 2- to 4-fold during locomotion at 11 cm s−1, and did not fatigue in 22 min of exercise at this speed. Animals with closed airways managed only small increases above the routine during exercise at 11 cm s−1, and none could sustain activity for more than 10 min. Thus, exclusively skinbreathing Ambystoma cannot increase cutaneous gas exchange to compensate for the elimination of pulmonary and buccopharyngeal respiration; locomotor stamina suffers accordingly. Small salamanders can apparently increase cutaneous gas exchange during activity, although large salamanders cannot, because cutaneous diffusing capacity and the resting oxygen requirement approach one another with increasing body size; the skin of large salamanders apparently has a limited scope for aerobic activity.
‘Steady’ Swimming Kinematics of Tiger Musky, an Esociform Accelerator, and Rainbow Trout, a Generalist Cruiser
Authors: Webb Paul W. 
Published: April 2021

ABSTRACTLocomotor kinematics of tiger musky (Esox sp.) and rainbow trout (Salmo gairdneri) were measured at ‘steady’ swimming speeds of up to 85 cm s−1. Tail beat frequencies of musky were approximately 2 Hz higher than those of trout at any swimming speed, but tail beat amplitudes were 0·04L (where L is total body length) smaller. The product of these two variables was similar for the two species at any speed. The length of the propulsive wave was independent of speed, and was 0·8L for musky, somewhat smaller than the value for trout, 0·9L. The depth of the caudal fin trailing edge of trout was greater than that of musky, but the greater depth of the posteriorly located median fins of musky also contributed to thrust production. The cosine of the angle of the trailing edge to its beat plane showed the same phase relationship with lateral displacement in both musky and trout. It increased with speed for both species, and values for musky were slightly smaller. Thrust power requirements of musky and trout were similar. Thrust (= drag) coefficients of musky were 1·55 times larger than those for trout: this is roughly as expected on the basis of the larger proportion of the total area of musky located caudally and the higher drag coefficients in this region of the body. Lateral recoil movements of musky were unexpectedly smaller than for trout and were associated with smaller energy wastage from undamped recoil movements. The large recoil expected for the body form of musky was damped to some extent by higher tail beat frequencies, although this entailed some loss in Froude efficiency. Otherwise, no hydrodynamic explanation for the small recoil movements of musky was apparent. It is suggested that the myotomal muscles could be involved in minimizing recoil. The esociform morphology incurs costs in steady swimming, in comparison with generalist cruises, because of reduced sprint speeds for fish of a given length or increased power requirements for fish of a given mass.
Actions of dendrotoxin on K+ channels and neuromuscular transmission in Drosophila melanogaster, and its effects in synergy with K+ channel-specific drugs and mutations
Authors: Wu Chun-Fang , Tsai Ming-Cheng , Chen Mai-Lei , Zhong Yi , Singh Satpal , Lee C. Y. 
Published: April 2021

ABSTRACT
The blockade of K+ channels and enhancement of neuromuscular transmission by dendrotoxin (DTX), a convulsant peptide from mamba snake venom, were examined in normal and mutant larval preparations of Drosophila. Two-microelectrode voltage-clamp experiments showed that DTX reduced the transient K+ current, IA, in muscle membrane. This effect was suppressed by raising the Mg2+ concentration or by lowering the temperature. The interaction of DTX with Mg2+ was further analyzed at a low cation concentration, at which DTX reduced both IA and the delayed rectifier IK. These results were correlated with the action of DTX on the neuromuscular junction. Its facilitatory effect on excitatory junctional potentials (EJPs) was relatively mild but the effect was drastically enhanced when combined with certain mutations and K+ channel blocking drugs, leading to repetitive or prolonged giant EJPs. Only the mutations or drugs that reduced IK or the Ca2+-dependent K+ current, ICF, could yield these synergistic effects with DTX. In contrast, the abnormal EJPs caused by the mutation or drug that blocked IA were not further enhanced by DTX, indicating that DTX also affects IA at the neuromuscular junction. Thus, the A-type K+ channels in muscle and nerve terminals appeared very similar in their sensitivity to the specific toxin, drugs and mutations examined here.
Interactions Between ion Exchange and Metabolism in Erythrocytes of the Rainbow TroutOncorhynchus Mykiss
Authors: Tufts B. L. , Boutilier R. G. 
Published: April 2021

ABSTRACTExperiments were carried out to investigate the relationship between ion exchange and energy metabolism in rainbow trout erythrocytes in vitro. Under resting conditions, the sodium/potassium pump accounts for 20% of the cellular energy budget. In the presence of the β-adrenergic agonist isoproterenol, however, this increases to 43%. Inhibition of the sodium/potassium pump with ouabain results in greater increases in erythrocyte water content and sodium and chloride concentrations and a greater decrease in erythrocyte potassium concentration following stimulation by isoproterenol. Moreover, the decrease in erythrocyte NTP levels observed following adrenergic stimulation does not occur when the sodium/potassium pump is inhibited with ouabain. Inhibition of the sodium/ potassium pump also abolishes the increase in oxygen consumption by the cells which normally takes place following adrenergic stimulation. Finally, depletion of erythrocyte NTP levels by the sodium ionophore monensin or by previous incubation with nitrogen does not result in a significant increase in oxygen consumption. Thus, catecholamines appear to be crucial for the metabolic-membrane coupling that occurs following adrenergic stimulation in rainbow trout erythrocytes.
Activities of Enzymes for Glucose Catabolism in the Swimbladder of the European EelAnguilla Anguilla
Authors: Pelster Bernd , Scheid Peter 
Published: April 2021

ABSTRACTGas secretion into the swimbladder of the eel relies on the production of CO2 and lactic acid from glucose in the swimbladder epithelium. The activities of the enzymes involved in glucose catabolism have been measured and compared with those in the rete mirabile, the liver and white skeletal muscle to evaluate whether the pentose phosphate shunt may contribute to glucose metabolism in the swimbladder tissue. The activities of enzymes of the pentose phosphate shunt were higher in the swimbladder epithelium than in white muscle, and close to those in the liver. The activities of the enzymes of anaerobic glycolysis were 2–5 times higher in the swimbladder epithelium than in the rete mirabile, reaching or even exceeding the levels in liver and white muscle, whereas the activities of the enzymes of oxidative metabolism were extremely low. Compared to enzymes of the other tissues, swimbladder phosphofructokinase and glucose-6-phosphate dehydrogenase showed no special adaptation to low pH values. The results show that the swimbladder epithelium is equipped with enzymes that produce CO2 from glucose without the removal of O2, which is particularly advantageous for creating the high gas partial pressures needed for filling the swimbladder at great depth.
Desensitization of Adrenaline-Induced Red Blood Cell H+ Extrusion in Vitro After Chronic Exposure of Rainbow Trout to Moderate Environmental Hypoxia
Authors: Thomas S. , Kinkead R. , Walsh P. J. , Wood C. M. , Perry S. F. 
Published: April 2021

ABSTRACT
The sensitivity of red blood cell Na+/H+ exchange to exogenous adrenaline was assessed in vitro using blood withdrawn from catheterized rainbow trout (Oncorhynchus my kiss) maintained under normoxic conditions [water or after exposure to moderate hypoxia for 48 h, which chronically elevated plasma adrenaline, but not noradrenaline, levels. Peak changes in whole-blood extracellular pH over a 30 min period after adding 50–1000 nmol l−1 adrenaline were employed as an index of sensitivity; the blood was pre-equilibrated to simulate arterial blood gas tensions in severely hypoxic fish . Blood pooled from normoxic fish displayed a dose-dependent reduction in whole-blood pH after addition of adrenaline. Blood pooled from three separate groups of hypoxic fish, however, displayed diminished sensitivity to adrenaline, ranging from complete desensitization to a 60% reduction of the response. Subsequent experiments performed on blood from individual (i.e. not pooled) normoxic or hypoxic fish demonstrated an inverse correlation between the intensity of H+ extrusion (induced by exogenous adrenaline addition) and endogenous plasma adrenaline levels at the time of blood withdrawal. However, acute increases in plasma adrenaline levels in vitro did not affect the responsiveness of the red blood cell to subsequent adrenergic stimulation. The intensity of H+ extrusion was inversely related to the in vivo between 2.67 and 10.66 kPa, and directly related to the logarithm of the endogenous plasma adrenaline level. The results suggest that desensitization of Na+/H+ exchange in chronically hypoxic fish is related to persistent elevation of levels of this catecholamine. This desensitization can be reversed in vitro as a function of time, but only when blood is maintained under sufficiently aerobic conditions.
Hydrodynamics of Rapid Shell Closure in Articulate Brachiopods
Authors: Ackerly Spafford C. 
Published: April 2021

ABSTRACTThe rapid shell-closing mechanism in articulate (hinged) brachiopods is subject to important hydrodynamic constraints related to expulsion of water from the shell. Fluid forces influence, for example, the speeds of shell closure and the mass flux rates of water from the shell. The principal hydrodynamic forces acting on a shell during rapid closure are (1) inertial reactions, due to the acceleration of water (=acceleration reaction), and (2) water pressure forces which develop as water is expelled from the shell. A generalized hydrodynamic model describes the relative magnitudes of the acceleration and pressure forces as functions of the shell’s angular acceleration, velocity and gape. In general, the acceleration reaction dominates the kinematics of shell closure during the initial phases of a closing event, whereas pressure forces dominate towards the later phases of shell closure. Solutions of the general model predict how variables such as the closing speed and the mass flux of water depend on shell size, initial shell gape and on the magnitude of the closing force. Results indicate that inertial reactions (due to acceleration of water) dominate the mechanics of shell closure in articulate brachiopod taxa.
Effect of γ-Aminobutyric Acid on Intracellular pH in the Crayfish Stretch-Receptor Neurone
Authors: Voipio J. , Pasternack M. , Rydqvist B. , Kaila K. 
Published: April 2021

ABSTRACTThe effect of γ-aminobutyric acid (GABA) on intracellular pH (pHi) was examined in the crayfish stretch-receptor neurone using H+-selective microelectrodes and a two-microelectrode voltage clamp. In the presence of 30 mmol I−1 HCO3− (pH 7.4), application of GABA (0.5 mmol I−1) produced a mean fall in pHi of 0.26 units. The initial rate of fall of pHi was attributable to a net influx of acid equivalents of 6.3 mmol I−1 min−1. In the nominal absence of HCO3−, GABA had little effect on pHi. The HCO3−-dependent acidosis caused by GABA was inhibited by picrotoxin (0.1 mmol I−1) but not by depletion of extracellular and intracellular Cl−. Acetazolamide (0.1 mmol I−1) decreased the rate of fall of pHi caused by a step increase in CO2 partial pressure as well as by GABA, which indicates that the neurone contains carbonic anhydrase. In the presence of both Cl− and HCO3−, the reversal potential of the GABA-activated current was more positive than under nominally HCO3−-free conditions. In line with this, GABA induced a marked HCO3−-dependent depolarization, and this depolarizing action was enhanced in the absence of Cl− so as to lead to triggering of action potentials. All these observations support the conclusion that the GABA-induced fall in pHi is due to a net efflux of HCO3− through the inhibitory anion channels.
Microcalorimetric Investigations on the Energy Metabolism of Lizards
Authors: Lamprecht I. H. D. , Matuschka F.-R. , Schaarschmidt B. 
Published: April 2021

ABSTRACTThe energy metabolism of three lizard species (Podarcis milensis, Podarcis muralis and Lacerta agilis) was investigated by means of microcalorimetry and polarography over the range of environmental temperatures between 17 and 35 °C encountered by active lizards during summer in Europe. In non-stimulated animals, the maximum and mean heat production rates were highest around 30°C for all species and amounted to 3.9±l.lmWg−1 and 2.1±0.5mWg−1, respectively. Resting metabolism contributed approximately 60% to the mean routine heat dissipation; the remainder originated from locomotory activity, 43% of which was based on anaerobic energy metabolism. From simultaneous determinations of heat dissipation and oxygen consumption, an average oxycaloric equivalent of 18.6±3.2 J ml−1O2 was calculated, which rose to 26.6±7.1 J ml−1O2 during short bursts of locomotion.
Metabolic and Enzymatic Heterogeneity in the Liver of the Ureogenic Teleost Opsanus Beta
Authors: Mommsen Thomas P. , Walsh Patrick J. 
Published: April 2021

ABSTRACT
Viable toadfish hepatocytes were separated into distinct subpopulations by gradient centrifugation. Although 3–5 density subpopulations were obtained for each fish, only two metabolically and enzymatically different subpopulations could be discerned. In all cases, hepatocytes with the lowest density (less than 1.040 g ml− 1) were more oxidative in scope, as judged by the activities of mitochondrial enzymes (citrate synthase, aspartate aminotransferase, glutamate dehydrogenase); activities of these enzymes (normalised to cell protein) were on average two-to threefold higher than in subpopulations with higher densities. Lower-density hepatocytes also contained higher levels of the urea cycle enzymes arginase and ornithine carbamoyltransferase. The higher-density subpopulations showed no significant differences from each other in enzymatic activities. Compared with lower-density cells, these hepatocytes had higher activities of two cytosolic enzymes, malate dehydrogenase and glutathione-S-transferase. There was no distinct distribution pattern for alanine aminotransferase and glutamine synthetase. Despite generally lower oxidative enzyme content, higher-density hepatocytes were metabolically more active, with 2.5-to fourfold higher rates of urea synthesis, gluconeogenesis and oxidation of lactate. We conclude that, although the toadfish liver shows distinct enzymatic and metabolic heterogeneity, this heterogeneity is dissimilar to the zonation pattern in the livers of mammals, in that separated toadfish hepatocyte types did not appear to possess exclusive metabolic functions. Notably, all cells were capable of metabolic functions that are strictly localised in mammalian liver. In nitrogen metabolism, glutamine synthetase displays a distribution pattern commensurate with its unique metabolic function in the liver of the ureogenic toadfish. Further, all subpopulations possessed detoxification capabilities as indicated by high levels of glutathione-S-transferase, a ‘phase II’ conjugation enzyme.
Studies on the Regulation of Enzyme Binding During Anoxia in Isolated Tissues ofBusycon Canaliculatum
Authors: Brooks Stephen P. J. , Storey Kenneth B. 
Published: April 2021

ABSTRACTThe role of pH and protein kinase second messengers in triggering or potentiating anoxia-linked changes in enzyme binding to particulate matter were evaluated using in vitro incubations of isolated ventricle strips of Busycon canaliculatum (L.) (Prosobranchia, Melongenidae). Incubating whelks under anoxic conditions for 4h reduced the percentage of phosphofructokinase (PFK), aldolase, glyceraldehyde 3-phosphate dehydrogenase (GAPDH) and pyruvate kinase (PK) activity associated with cellular particulate matter. Triose phosphate isomerase, phosphoglycerate kinase, phosphoglyceromutase and enolase showed no changes in enzyme binding when whelks were subjected to anoxic stress in vivo. Incubating isolated ventricle strips in vitro under anoxic conditions simulated the changes seen in vivo in whole, anoxic whelks with respect to the percentage of PFK and PK bound during anoxic stress; both whole-animal studies and isolated tissue studies showed reduced PFK and PK binding after 4 h of anoxic incubation. Tissue pH could be artificially changed by incubating isolated ventricle strips in sea water buffered to a desired pH. This permitted an investigation of the effect of intracellular pH on PFK and PK binding in situ. PFK and PK responded to altered intracellular pH with increased enzyme binding at lower intracellular pH values and decreased enzyme binding at higher intracellular pH values. These binding patterns were exactly the opposite of those observed during anoxia; during anoxia stress, both intracellular pH and the percentage of PFK and PK associated with particulate matter decreased. Addition of the second messenger compounds dibutyryl cyclic AMP, dibutyryl cyclic GMP or phorbol 12-myristate 13-acetate plus the calcium ionophore A23187 had no effect on the percentage of activity bound to subcellular structures measured under either normoxic or anoxic conditions. This study suggests that enzyme binding in vivo is not regulated by changes in intracellular pH or concentrations of protein kinase second messenger compounds during anoxia.