bluuebunny/crossref_metadata_2025_split huggingface dataset:
The In Vitro Effect of Hypoxia on the Trout Erythrocyte β-Adrenergic Signal Transduction System
Authors: Reid Scott D. , Lebras Y. , Perry S. F. 
Published: April 2021

ABSTRACT
We have investigated the effects of acute in vitro hypoxia on trout (Oncorhynchus mykiss) erythrocytes in order to elucidate the mechanism(s) by which increased catecholamine responsiveness of the Na+/H+ antiporter is achieved. Blood was withdrawn from cannulated trout and maintained in vitro under normoxic or hypoxic conditions for 30min prior to exposure to concentrations of noradrenaline, forskolin or 8-bromo-cyclic AMP ranging from 0 to 10−6 mol l−1, 10−7 to 10−5 mol l−1 or 10−4 to 10−2 mol l−1, respectively. Na+/H+ exchange activity was quantified as the maximal reduction in whole-blood pH (pHe) after addition of the various Na+/H+ antiporter activators. Erythrocyte intracellular cyclic AMP contents were also determined after addition of noradrenaline or forskolin. To complete the investigation, radioreceptor binding assays were conducted on separate blood samples to characterize the numbers and affinities of the surface population of β-adrenoceptors of erythrocytes maintained under normoxic or hypoxic conditions.
Exposure of erythrocytes to noradrenaline, forskolin or 8-bromo-cyclic AMP resulted in dose-dependent reductions in pHe as a result of Na+/H+ antiporter activation. In all cases, the effects were significantly more pronounced under hypoxic than normoxic conditions. Hypoxia significantly increased the production of cyclic AMP in the presence of noradrenaline but did not affect the forskolin-induced production of cyclic AMP. Blood oxygen status also affected the number of β-adrenoceptors expressed at the erythrocyte surface; hypoxic erythrocytes possessed 880.7±28.6 (N=6) receptors per cell whereas normoxic erythrocytes possessed 532.6±43.2 (N=6) receptors per cell.
These results suggest that in vitro exposure of trout erythrocytes to hypoxic conditions results in at least two significant alterations in the catecholamine signal transduction system: (1) an enhancement in erythrocyte cyclic AMP production, in part by virtue of an increase in the number of surface β-adrenoceptors, and (2) a hypoxia-induced increase in the cyclic AMP sensitivity of one or more of the steps culminating in Na+/H+ antiporter activation. These events ultimately increase the responsiveness of the erythrocyte Na+/H+ antiporter to catecholamines during hypoxia.
Glycogen Loss in Rat Muscles During Locomotion on Different Inclines
Authors: Armstrong R. B. , Taylor C. R. 
Published: April 2021

ABSTRACT
Running downhill causes structural damage in deep slow-twitch extensor muscles of the limbs. Both mechanical and metabolic hypotheses have been proposed to explain the damage. The purpose of this study was to use measurements of glycogen loss in the muscles and metabolic rates of rats running on the level and up and down 16° inclines at 26 m min−1 to try to distinguish between these hypotheses. Glycogen loss in the soleus and medial head to the triceps brachii muscles during running on the three inclines was proportional to whole-animal oxygen consumption, indicating that there were no unusual metabolic demands on these muscles during the downhill exercise. The minimum area of these muscles showing glycogen loss was smaller during downhill than during uphill running. Average forces in the muscles are similar during locomotion on different inclines at the same speed, suggesting that stresses in the active motor units were greater during downhill running. Thus, the results are more consistent with a mechanical than with a metabolic etiology for the muscle injury resulting from downhill running.
Mitochondrial Activity in Rainbow Trout Red Muscle: the Effect of Temperature on the Adp-Dependence of Atp Synthesis
Authors: Blier Pierre U. , Guderley Helga E. 
Published: April 2021

ABSTRACT
By coupling mitochondrial ATP production to an enzymatic NADPH-producing reaction, we monitored the rates of ATP production spectrophotometrically. ATP production was coupled to the oxidation of malate and pyruvate. Interference by adenylate kinase was eliminated by using P1,P5-di(adenosine-5′)pentaphosphate and we found no interference by NADPH oxidase. We studied the kinetics of ATP synthesis by mitochondria from rainbow trout red muscle at three temperatures (8, 15 and 22°C) and under two pH regimes (a constant pH of 7.4 and temperature-dependent pH). The mitochondria oxidized pyruvate and malate. The apparent Michaelis constant (Km,app) for ADP as well as the maximal velocity (Vmax) for ADP phosphorylation are markedly affected by temperature but not by pH. The Km,app for ADP decreases with increasing temperature while the Vmax increases. These data suggest that reduced temperatures decrease mitochondrial sensitivity to control by ADP availability.
Influence of Dietary Sodium and Other Factors on Plasma Aldosterone Concentrations and in Vitro Properties of the Lower Intestine in House Sparrows (Passer Domesticus)
Authors: Goldstein David L. 
Published: April 2021

ABSTRACT
House sparrows ( Passer domesticus) had plasma aldosterone concentrations of about 180pgml−1 while maintained on a low-sodium diet (LS, 0.1mequiv Na+ ingested per day), 135pgml−1 on a sodium intake of 0.9mequivday−1 (high-salt diet, HS) and 45pgml−1 on a Na+ intake of 3.8mequivday−1 (high-salt diet with saline drinking water, HSS). The plasma concentration of aldosterone changed to the LS or the HS level within 1 day of switching from the HS or the LS diet, respectively. Neither dehydration (22h, 14.5% loss in body mass) nor brief periods of stress (1–5min of handling) caused a change in circulating levels of aldosterone. The electrical properties of the lower intestine acclimated to the different sodium intakes with a time course similar to that of the changes in aldosterone levels. On the LS diet, the lower intestine generated an electrical potential difference (PD) of 5mV (lumen negative) and a short-circuit current (Isc) of about 50 μA cm−2; these were consistently inhibited by amiloride (resulting in a lumen-positive PD) and were stimulated by glucose or amino acids (leucine and lysine) in about half of the tissues. In HS birds, the PD and Isc were abolished and the effects of glucose and amino acids were reduced, but amiloride still caused a significant change in transmural PD (to a mucosa-positive value). These properties resemble those of the chicken coprodeum more than they do those of chicken colon, although the tissues tested were from the mid-region of the large intestine and their histology resembled that of colon. Sparrows tested immediately upon capture from the wild had plasma aldosterone levels not significantly different from those of birds on the LS diet, which is consistent with the known diet of this species. However, Isc was higher and tissue resistance was lower in wild birds compared with low-salt birds in the laboratory, perhaps indicating the influence of other hormones in addition to aldosterone.
Contractile Properties of the Striated Adductor Muscle in the Bay Scallop Argopecten Irradians At Several Temperatures
Authors: Olson John M. , Marsh Richard L. 
Published: April 2021

ABSTRACT
The isometric and isotonic contractile properties of the cross-striated adductor muscle of the bay scallop (Argopecten irradians) were measured in vitro at 10, 15 and 20°C. The length at which twitch force was maximal as a function of the closed length in situ (L0/Lcl) averaged 1.38±0.01 (mean ± S.E.M.) at 10°C. This length is very close to the typical length at maximum gape during natural swimming at this temperature. Passive force was very low over the range of lengths measured here; at L0, passive force averaged approximately 0.08 N cm−2, or only 0.5% of the corresponding peak twitch force. The mean peak isometric twitch force (Ptw,max) at 10°C was 21.43±0.68 N cm−2 (S.E.M.), and the ratio of peak twitch force to tetanic force (Ptw,max/P0) averaged 0.89±0.01. Temperature did not affect either twitch force (Ptw), once fatigue was taken into account, or Ptw,max/P0. In contrast, the time-related properties of twitch contractions (latent period, tL; time to peak tension, tPtw; and time from peak tension to half-relaxation, t50%R) were positively modified by temperature at all temperatures measured (Q10&gt;1.8). All three properties were more temperature-sensitive over the range 10–15°C than over the range 15–20°C.
The force–velocity relationships of the striated adductor muscle were fitted to the hyperbolic-linear (HYP-LIN) equation. The force–velocity curves of the striated adductor muscle of the scallop were strongly influenced by temperature. Maximal velocity at zero force (Vmax), and therefore maximal power output, increased significantly with temperature. The Q10 over the temperature range 10–15°C (1.42) was significantly lower than that over the range 15–20°C (2.41). The shape of the force–velocity relationship, assessed through comparisons of the power ratio (Ẇmax/VmaxP0), was not influenced by temperature.
The Physiology of the Alligator Heart: Left Aortic Flow Patterns and Right-To-Left Shunts
Authors: Jones David R. , Shelton Graham 
Published: April 2021

ABSTRACT
Blood pressures have been recorded in the heart along with pressures and flow in the aortic arches of anaesthetized and awake alligators. Systemic blood pressures were significantly lower [5.22±0.57kPa (N=3) versus 9.85±0.46kPa (N=5)] and cardiac outputs higher [51.6±3.5mlmin−1 kg-1 (N=3) versus 25.5±8.2mlmin−1 kg-1 (N=5)] in awake compared with anaesthetized animals. Using pharmacological interventions, two types of right-to-left shunt could be induced in all alligators. In one, established after acetylcholine (ACh) injection into the right side of the circulation, left aortic flow was an anterograde monophasic pulse which occurred when pulmonary pressure exceeded systemic blood pressure. Hence, this left aortic flow pattern could also be induced by mechanical occlusion of both pulmonary arteries. About one-quarter of cardiac output could bypass the lungs during this shunt. However, this left aortic flow pattern was never seen under any conditions other than pharmacological intervention. In the other type of shunt, induced pharmacologically by ACh injection into the left side of the circulation, left aortic flow was biphasic with a period of backflow, initiated during systole, being progressively shortened by the onset of forward flow from the right ventricle. Establishment of this type of shunt depended on the magnitude of both the systemic pressure and the pressure generated by right ventricular contraction after closure of the pulmonary outflow tract. The amount of blood bypassing the lungs during this shunt was small (13.7±5% of cardiac output) but, at maximum, could be almost 25% of cardiac output. This shunt occurred naturally in resting animals and could be maintained for substantial periods (13.2min). The present observations confirm those made previously on anaesthetized alligators and extend previous work by showing two potential types of shunt. Finally, we suggest that right-to-left blood shunting in crocodilians may be related to the ‘alkaline tide’ that occurs after feeding, so the unique design of the central cardiovascular system in crocodilians could relate to both gastrointestinal and cardiorespiratory physiology.
Plateau Potentials in an Insect Motoneurone can be Driven by Synaptic Stimulation
Authors: Hancox Jules C. , Pitman Robert M. 
Published: April 2021

ABSTRACT
Cyclical patterns of behaviour such as respiration and locomotion are generated by groups of neurones whose output depends not only upon their synaptic interconnections but also on the intrinsic membrane properties of individual cells. For example, the ionic conductances of some neurones in rhythm-generating circuits allow these cells to respond to non-patterned excitatory synaptic drive with ‘plateau’ or ‘driver’ potentials: prolonged, regenerative depolarizations which can drive bursts of impulses and, thereby, contribute to characteristics of the motor rhythm (Russell and Hartline, 1978, 1982; Tazaki and Cooke, 1979a–c, 1983a–c, 1986, 1990). Plateau potentials are not restricted to interneurones of the central pattern generator; they may also be recorded from motoneurones, which form the final output to muscles. Thus, plateau potentials have been recorded from locomotor motoneurones from the crayfish (Sillar and Elson, 1986), lamprey (Wallén and Grillner, 1987), cat (Hounsgaard et al. 1988) and turtle (Hounsgaard and Kiehn, 1989) (see also review by Kiehn, 1991).
Roles of Buffering Capacity and Pentose Phosphate Pathway Activity in the Gas Gland of the Gulf Toadfish Opsanus Beta
Authors: Walsh Patrick J. , Milligan C. Louise 
Published: April 2021

ABSTRACT
The teleost gas gland is truly remarkable in its abilities to secrete gases into the swim bladder of physoclistous fish. The physiological and metabolic adaptations of this tissue have been elegantly summarized in a recent review article by Pelster and Scheid (1992). There are two key contributors to the function of the gland. First, a specialized metabolism of the swim bladder, involving copious and simultaneous production of lactate and CO2 from anaerobic glycolysis and the pentose phosphate pathway (also known as the hexose monophosphate shunt), respectively, contributes to gas exchange through pH and salting-out effects on the oxygen-carrying capacity of the blood. Second, a countercurrent multiplier system (i.e. a rete mirabile) enables gas tensions to be elevated further by back diffusion. Several features of metabolism and acid–base physiology remain unclear. First, despite the remarkable ability of this tissue to produce acid, it is not clear if or how intracellular pH (pHi) is regulated. Since ultimately the blood must be acidified, one would predict that the pHi of the tissue would be well regulated via high rates of membrane exchange of protons and/or high tissue buffering capacity. Second, although the functioning of the pentose phosphate pathway has been strongly inferred from measurements of enzyme activities (Boström et al. 1972; Pelster and Scheid, 1991), and from measurements of enhanced rates of CO2 excretion relative to the rates of oxygen uptake (Pelster et al. 1989), direct evidence for the existence of the shunt is lacking. Lastly, although the pentose phosphate pathway is expected to produce CO2, and thus contribute to the acidification of blood entering the gland, the pathway may have a different primary, or perhaps a dual, role, namely to maintain high tissue levels of NADPH for protection against oxygen radical damage to cells (Pelster and Scheid, 1992). The composition of the gas stored in the swim bladder can approach pure oxygen in some species, so it is not surprising that the teleost gas gland contains substantial levels of the enzymes catalase, superoxide dismutase and glutathione peroxidase, which scavenge deleterious radicals of oxygen and related harmful compounds (Morris and Albright, 1984). Noteworthy is glutathione peroxidase, which requires a constant supply of NADPH (presumably from the shunt) to maintain glutathione in a reduced state. Reduced glutathione is then used in a variety of oxygen radical detoxification mechanisms. If the pentose phosphate pathway has a role in oxygen detoxification, one would predict that flux rates through the pathway would increase with increased oxygen levels.
Calcium Channel Currents In Neurones From Locust (Schistocerca Gregaria) Thoracic Ganglia
Authors: Pearson H. A. , Lees G. , Wray D. 
Published: April 2021

ABSTRACT
Using the patch-clamp technique, Ca2+ channel currents were recorded from neurones freshly isolated from the thoracic ganglia of the desert locust Schistocerca gregaria. In solutions containing 10mmol l−1Ba2+ we observed high-voltage-activated whole-cell inward currents with sustained and transient components, both of which had similar steady-state inactivation properties. Substitution of Ca2+ for Ba2+ was found to reduce whole-cell currents, whereas removal of monovalent cations had no effect. Cd2+ (1mmol l−1) completely blocked the whole-cell current, but at 10 μmol l−1 preferentially inhibited the sustained component without affecting the transient component. Verapamil (1 μmol l−1) inhibited both current components but appeared to be more selective for the sustained component, whereas nitrendipine (1 μmol l−1) had no effect on either component. A single-channel recording suggested that the transient component was carried by a low-conductance channel. Certain compounds with insecticidal action (ryanodine, S-bioallethrin, deltamethrin and avermectin) did not affect calcium channel currents in these cells. These data suggest that there are two types of Ca2+ channels present in locust neurones. These channel types have properties differing from the T-, L- and N-type channels found in vertebrates and, furthermore, were not targets for the insecticides we tested.
The Regulation of Haemolymph Potassium Activity During Initiation and Maintenance of Diuresis in Fed Rhodnius Prolixus
Authors: Maddrell S. H. P. , O’donnell M. J. , Caffrey R. 
Published: April 2021

ABSTRACT
The blood-sucking insect Rhodnius prolixus rapidly eliminates a Na+-rich K+-poor urine after its large meals. K+-rich fluid is first secreted by the upper Malpighian tubules and passes to the lower tubules where most of the potassium is reabsorbed.
During the initial stimulation of the tubules, the lower tubules must be activated first to avoid loss of potassium. The major element in this is that they respond more rapidly than do the upper tubules to particular hormonal concentrations rather than that they react to lower hormonal concentrations than do the upper tubules.
During subsequent diuresis, regulation of the haemolymph potassium concentration depends on three cooperative homoeostatic mechanisms in the tubules. A fall in potassium concentration of the medium bathing the tubules causes (i) a decrease in the rate of fluid secretion by the upper tubules, (ii) a decrease in potassium concentration in the fluid secreted by the upper tubules and (iii) an increase in the rate of potassium absorption by the lower tubules. The tubules respond in the opposite direction to an increase in potassium concentration of the medium. As a result, the potassium concentration of the urine can be adjusted to match the potassium concentration of the fluids absorbed from the gut, so that the potassium concentration of the insect’s haemolymph remains unaltered.
in vivo Utilization of Glucose by Heart and Locomotory Muscles of Exercising Rainbow Trout (Oncorhynchus Mykiss)
Authors: West Timothy G. , Arthur Peter G. , Suarez Raul K. , Doll Christopher J. , Hochachka Peter W. 
Published: April 2021

ABSTRACT
In vivo rates of glucose utilization were estimated in red muscle and heart of rainbow trout using the radiolabeled glucose analogue, [14C]-2-deoxyglucose ([14C]-2-DG). The 2-DG ‘lumped constant’ (LC), representing the uptake ratio between 2-DG and glucose for each tissue, was determined in vitro using tissue slices. For both red muscle and heart, the LC was approximately 0.40. In addition, changes in circulatory glucose utilization induced in an isolated trout heart preparation had no effect on the LC. The LC was applied to calculations of in vivo rates of circulatory glucose disposal in muscle tissue of resting and swimming trout. Utilization was estimated at 0.87±0.15 and 5.31±1.04nmol g−1 min−1 in red muscle and heart of resting fish, respectively. In trout swimming at 80 % Ucrit, glucose utilization in heart was unchanged compared to resting controls, while red muscle utilization increased by 28-fold. Estimates of the oxidative demand of heart and locomotory muscle of swimming trout indicate that glucose utilization accounted for less than 10% of the energy production in both tissues. In trout heart, in vitro measures of glucose flux suggest an apparent excess capacity to use circulatory glucose. Preference for other intra-and extramuscular fuels may partially explain limited glucose utilization, but it remains unclear to what degree, and under what conditions, glucose utilization may be increased in vivo.
Intracellular-Messenger-Mediated Cation Channels in Cultured Olfactory Receptor Neurons
Authors: Stengl Monika 
Published: April 2021

ABSTRACT
After 2–3 weeks in culture, pupal olfactory receptor neurons from the antennae of male Manduca sexta respond to their species-specific sex pheromone by opening cation channels. These pheromone-dependent cation channels are the only channels previously found in cultured olfactory neurons that promote inward currents at membrane potentials more negative than the resting potential. The pheromone-dependent currents depend on external Ca2+ concentration. They are inwardly rectified with 10−7 mol l−1 external Ca2+ and linear with 6mmol l−1 Ca2+. This paper shows that perfusion of cultured olfactory receptor neurons with GTPγS, ATP, inositol 1,4,5,-trisphosphate or 10−6moll−1 Ca2+ elicits cation currents resembling the pheromone-dependent cation currents in expressing inward rectification with 10−7 mol l−1 external Ca2+ and being linear at external Ca2+ concentrations of 2 μmol l−1 or more. Stimulation with protein kinase C also elicits cation currents that share properties with the pheromone-dependent cation currents. All agent-induced cation currents appear to depend either directly or indirectly on Ca2+concentration.
Metabolic Heat Production by Artemia Embryos Under Anoxic Conditions
Authors: Hontoria Francisco , Crowe John H. , Crowe Lois M. , Amat Francisco 
Published: April 2021

ABSTRACT
The metabolic status of encysted Artemia embryos under anoxic conditions has been studied by calorimetry. Previous work demonstrated a very low, but still measurable, source of metabolic heat (31nWmg-1 drymass) after 6 days of anoxia, attributed to the catabolism of small amounts of carbohydrate storage compounds and the unusual nucleotide diguanosine tetraphosphate. Our results indicate that the heat measured drops below the detection limits of our calorimeter (11nWmg-1 drymass) after 1.5h of anoxia, in sharp contrast with previously published results. The possible sources of error that could explain this difference, and a re-evaluation of the metabolic status of cysts during anoxia, are discussed. We conclude that if the cysts are carefully protected from oxygen they become essentially ametabolic.
Membrane Permeability and Utilization of L-Lactate and Pyruvate in Carp Red Blood Cells
Authors: Tiihonen Kirsti , Nikinmaa Mikko 
Published: April 2021

ABSTRACT
L-Lactate and pyruvate permeability and utilization in carp (Cyprinus carpio) red blood cells was studied in vitro with tracer methods. Transport of lactate and pyruvate across the carp red blood cell membrane is rapid. At low plasma concentrations, lactate and pyruvate are transported into carp red blood cells mainly via a specific monocarboxylate carrier. This is shown by a study of the saturation kinetics and by inhibition using α-cyano-4-hydroxycinnamic acid and, more powerfully, p-chloromercuriphenylsulphonic acid. At higher plasma concentrations both simple diffusion and, apparently, the band 3 anion exchange system become increasingly important transport pathways. Carbon dioxide production rates from lactate and pyruvate as a function of their extracellular concentrations showed saturation kinetics. The transport rates of lactate and pyruvate are considerably higher than those required for their maximal rate of oxidation. The rapid transport of lactate and pyruvate into carp red blood cells thus guarantees that substrate availability is not the rate-limiting factor for the oxidation of these substrates.