bluuebunny/crossref_metadata_2025_split huggingface dataset:
Anhydrobiosis in Embryos of the Brine Shrimp Artemia: Characterization of Metabolic Arrest During Reductions in Cell-Associated Water
Authors: Glasheen J. S. , Hand Steven C. 
Published: April 2021

ABSTRACT
Upon entry into the state of anhydrobiosis, trehalose-based energy metabolism is arrested in Artemia embryos (cysts). We have compared changes in the levels of trehalose, glycogen, some glycolytic intermediates and adenylate nucleotides in hydrated embryos observed under conditions of aerobic development with those occurring after transfer to 5·0mol 1−1 NaCl. This treatment is known to reduce cell-associated water into a range previously referred to as the ametabolic domain. The trehalose utilization and glycogen synthesis that occur during development of fully hydrated cysts are both blocked during desiccation. Upon return to 0·25 mol 1−1 NaCl both processes are resumed. Analysis of glycolytic intermediates suggests that the inhibition is localized at the trehalase, hexokinase and phosphofructokinase reactions. ATP level remains constant during the 6-h period of dehydration, as does the adenylate energy charge. An additional dehydration experiment was performed in 5·0moll−1 NaCl containing 50mmoll−1 ammonium chloride (pH9·0). The resulting level of gaseous ammonia in the medium has been shown to maintain an alkaline intracellular pH (pHi) in the embryos. The metabolic response to dehydration under these conditions was very similar to the previous dehydration series. Thus, these results are taken as strong evidence that the metabolic suppression observed during dehydration does not require cellular acidification, in contrast to the pronounced inhibitory role of low pHi during entry of hydrated embryos into the quiescent state of anaerobic dormancy. The arrest of carbohydrate metabolism seen during anhydrobiosis indeed appears to be a strict function of embryo water content.
Electrophysiology of K+ Transport by Midgut Epithelium of Lepidopteran Insect Larvae: II. the Transapical Electrochemical Gradients
Authors: Moffett David F. , Koch Alan R. 
Published: April 2021

ABSTRACT
The apical surface of the midgut of Manduca sexta larvae is composed of the apical membranes of columnar cells, in the form of microvilli, and the apical goblet of goblet cells. Considerable evidence has suggested that the apical electrogenic pump that is responsible for transepithelial K+ transport is located on the apical membrane of goblet cells. In the present study the transapical potentials and K+ chemical activity [(K+)] gradients of columnar and goblet cells of posterior midgut were examined in the short-circuited gut. In some experiments the recording site was localized by ionophoresis of NiCl2 followed immediately by fixation in rubeanic acid.
The (K+) of goblet cavities was substantially higher than that of the free solution on the gut luminal side (mean value of 94mmol 1-1 in standard bathing solution). The goblet cavity was electrically positive to the gut lumen (mean value of 40 mV in standard bathing solution). When the rate of pumping of K+ into the goblet cavity was decreased by hypoxia or decreased bathing solution [K+], the electrical potential gradient between cytoplasm and goblet cavity decreased while intracellular (K+) and goblet cavity (K+) were relatively stable. These studies provide evidence that a negatively charged goblet matrix is present in goblet cavities. Furthermore, they suggest that it is the voltage-sensitivity of the apical pump to the electrical component of the transapical electrochemical gradient, and not a concentration-dependence of the pump, that exercises the major role in determining the relationship between extracellular (K+) and net K+ transport by the isolated gut.
Delayed Effects of Anoxia Upon the Electrical Properties of an Identified Cockroach Motoneurone
Authors: Pitman Robert M. 
Published: April 2021

ABSTRACT
In nerve preparations isolated from cockroaches that had survived exposure to carbon dioxide or nitrogen for 1–3 h, the cell body of the metathoracic ‘fast’ coxal depressor motoneurone (Df) gained the ability to support all-or-none action potentials. Such responses were observed between 10 h and 5 days after the anoxic period. Recordings from isolated cell bodies indicated that the action potentials were generated in the cell body itself rather than in adjacent regions of the neurone. Action potentials were abolished in a sodium-free medium or in the presence of tetrodotoxin, but persisted in saline containing manganese ions, indicating that sodium ions are the major ions involved in the rising phase of these action potentials. Elevation of the intracellular H+ concentration by acid injection or by bathing the preparation in saline containing 40 mmol 1−1 ammonium chloride caused a marked depolarization of the membrane potential and action potentials could not be elicited. This indicates that a fall in intracellular pH during anoxia could not itself directly produce the enhancement in excitability reported here. Histological examination of the neurone, after periods of anoxia sufficient to enable the cell body to generate the action potentials reported here, showed no detectable change in the perinuclear distribution of RNA and hence did not indicate any alteration in protein synthesis.
Fluid Mechanical Valving of Air Flow in Bird Lungs
Authors: Kuethe Dean O. 
Published: April 2021

ABSTRACT
The unidirectional flow through the gas-exchanging bronchi of bird lungs is known to be effected by (1) the structure of the major bronchi and (2) a pressure difference between the cranial and caudal air sacs.
To study the effects of bronchial structure, simple physical models of bird lungs were constructed. They suggested that, to achieve unidirectional flow, air in the caudal portion of the primary bronchus must be directed towards the orifices of the mediodorsal bronchi.
To study the effect of air sac pressures, a controllable pressure difference was produced between the air sac orifices of fixed duck lungs. The cranial orifices had a higher pressure than the caudal ones during inhalation and vice versa during exhalation. There was a set of pressure differences for which the paleopulmo received the same flow rate during inhalation as during exhalation. High pressure differences caused more flow in the paleopulmo during exhalation than during inhalation; low pressure differences had the converse effect.
The Distribution of Ammonia and H+ Between Tissue Compartments in Lemon Sole (Parophrys Vetulus) at Rest, During Hypercapnia and Following Exercise
Authors: Wright P. A. , Randall D. J. , Wood C. M. 
Published: April 2021

ABSTRACT
The distribution of ammonia and [146C]DMO was compared in white muscle, heart, brain, red cells and plasma of lemon sole (Parophrys vetulus Girard) at rest, during hypercapnia and following strenuous exercise. In red cells at rest, measured intracellular ammonia levels were equal to those predicted by the plasma to red cell pH gradient. Red cells are unusual in that hydrogen ions are passively distributed according to membrane potential (EM), whereas in other tissues this is not the case. In white muscle, heart and brain under all experimental conditions, intracellular ammonia levels far exceed those predicted by transmembrane pH gradients. Calculated values in these tissues are very close to published resting values of EM. We conclude that, in lemon sole, NH4+ permeates cell membranes and that intracellular ammonia stores are not determined by transmembrane pH gradients.
Distribution of Amino Acids to Internal Tissues After Epidermal Uptake in the Annelid Glycera Dibranchiata
Authors: Qafaiti Michael , Stephens Grover C. 
Published: April 2021

ABSTRACT
Net uptake rates by Glycera dibranchiata Ehlers of 18 amino acids, each present in artificial sea water at an initial concentration of 1 μmol 1-1, were estimated using high-performance liquid chromatography (HPLC). Uptake rates for 14C-labelled alanine, arginine, aspartate, glutamate, glycine and serine, presented singly at an initial concentration of l μmoll−1, were estimated by observing disappearance of radioactivity from the ambient solution. Net entry of alanine, arginine, aspartate and serine was estimated by HPLC in parallel samples of the medium. There was no significant difference in the rate of influx of labelled substrate and net entry estimated by HPLC for these amino acids. Ligature of the anterior and posterior ends of the worms did not perceptibly modify rates of uptake. Distribution of radioactivity to the internal and external body wall, coelomocytes, gut and coelomic fluid was observed after lh of incubation in lμmol11 serine. Rates of exchange of labelled carbon were estimated for all combinations of these internal tissues by taking advantage of morphological features of Glycera. Amino acid pools in each of the tissues of the worms are described, based on HPLC analyses. Internal distribution of radioactivity derived from [14C]serine is com-pared with total pools based on estimates of tissue volume and the normal serine content of free amino acid pools for each tissue. The distribution of the non-metabolized analogue cycloleucine is also described at the end of lh of incubation.
The Cooling Power Of Pigeon Legs
Authors: Martineau Lucie , Larochelle Jacques 
Published: April 2021

ABSTRACT
The rate of heat loss from legs and feet (ḢLEG) was studied in resting pigeons preheated to a body temperature (43·1 °C) close to those recorded during flight. The experimental system was designed to allow the calculation of ḢLEG from whole-body cooling rates following exposure of the legs and feet to various combinations of wind speed (0–75 km h−1) and air temperature (5–25°C). The pigeons remained hyperthermic when their hindlimbs were kept insulated, but their bodies cooled markedly as a result of exposure of the legs and feet. With a 12·5kmh−1 wind at 25°C, ḢLEG corresponded to 240% of the resting heat production. HLEG was increased by higher wind speed and lower air temperature, but it became essentially independent of wind speed above 37·5 km h−1. The maximum values of ḢLEG were 4–6 times as large as the resting heat production and could account for 50–65 % of the total heat produced during flight. It is concluded that in a non-aquatic bird the legs and feet can play a major role in whole-body thermoregulation, both at rest and during flight.
Physiological Correlates of Interspecific Variation in Acid Tolerance in Fish
Authors: Freda J. , Mcdonald D. G. 
Published: April 2021

ABSTRACT
This study investigated ion regulation in relation to water pH in three species of fish of differing tolerance to low pH (common shiners, Notropis cornutus, most sensitive; rainbow trout, Salmo gairdneri, intermediate; yellow perch, Perea flavescens, least sensitive). Increasing sensitivity to exposure to low pH was characterized by shorter survival times, greater losses of whole-body ions, more complete inhibition of Na+ uptake, and greater stimulation of Na+ efflux, the latter being the most important factor in determining survival. Interspecific variations in acid tolerance were also correlated with Na+ transport characteristics at circumneutral pH; Km was directly correlated Vmax and inversely correlated with acid tolerance. In addition, there were large qualitative differences among the species in the Ca2+-dependence of Na+ efflux. Sodium efflux induced by low pH was markedly Ca2+-dependent in both trout and shiners in a manner consistent with a simple competition between Ca2+ and H+ for gill binding sites. The increased sensitivity of shiners relative to trout was related to lowered Cam binding activity. In contrast, Na+ efflux in perch was virtually unaffected by water [Ca2+], Similarly, La3+ (a Ca2+ antagonist) stimulated higher Na+ losses from shiners than from trout, but had little effect upon perch. Ionic losses produced by saturating La3+ concentrations were generally lower than those produced by H+, suggesting that Ca2+ displacement is not the only mechanism for increased gill permeability at low pH. Nonetheless, the results obtained are consistent with the notion that acid tolerance may be related to Ca2+-binding activity in some species (e.g. trout and shiners) although not in others (e.g. perch).
Unpaired Median Neurones in a Lepidopteran Larva (Antheraea Pernyi): I. Anatomy And Physiology
Authors: Brookes S. J. H. , Weevers R. DE G. 
Published: April 2021

ABSTRACT
The anatomy and physiology of two unpaired median neurones (MCI and MC2) with bilaterally symmetrical axons in abdominal ganglia 3, 4, 5 and 6 of Antheraea pernyi larvae were studied. Intracellular dye filling of MCI and MC2 revealed that they were distinguishable from all other neurones in the ganglia and that they both had axons projecting out of the ganglia in right and left nerves 1. The two cells were identical in their central anatomy and physiology, but could be distinguished from one another by their peripheral branching patterns. The significance of these patterns was investigated by detailed study of the neural and muscular anatomy of the proleg-bearing segments 3, 4, 5 and 6. The peripheral axons of MCI and MC2 were exclusively associated with nerve trunks that could be traced to blocks of muscle.
Intracellular recordings of the two median cells characteristically showed overshooting soma action potentials that were followed by a long afterhyperpolarization lasting many seconds. Simultaneous recordings from median cells in the same ganglion revealed that MCI and MC2 shared an excitatory synaptic drive that largely determined their patterns of firing. Recordings from median cells in different ganglia showed that the common synaptic drive was also shared by median cells in different segments. Selective lesions of the ventral nerve cord indicated that the synaptic drive to MCI and MC2 originated in the suboeso-phageal ganglion. These cells were similar in anatomy and physiology to the median cells in several other insects.
Muscle Forces During Locomotion in Kangaroo Rats: Force Platform and Tendon Buckle Measurements Compared
Authors: Biewener Andrew A. , Blickhan Reinhard , Perry Andrew K. , Heglund Norman C. , Taylor C. Richard 
Published: April 2021

ABSTRACT
The muscle forces and stresses occurring during normal locomotor activity in kangaroo rats are compared with the peak isometric force developed by the same muscles in situ. Two methods were used simultaneously to determine the stresses (force/cross-sectional area) acting in the ankle extensors during steady-speed hopping and during jumps when animals were startled: a direct measurement using a force buckle surgically implanted around a tendon; and an indirect measurement using a force platform/ciné analysis technique. We obtained essentially the same values with the two techniques. We found that at slow speeds (0·7ms−1) the ankle extensor muscles of kangaroo rats exerted 20% of the maximum isometric force developed when the muscles were stimulated via the tibial nerve. This increased to 53% at higher speeds (l·9 ms−1). At the animal’s preferred hopping speed (1·5 ms−1), peak force was approximately 40% of maximum isometric force. In jumps when animals were startled, peak forces as high as 175% of the maximal elicited isometric force were recorded. These high forces always occurred when the muscles were being stretched. It appears that kangaroo rats utilize nearly the entire range of muscle force possible during normal locomotor events (i.e. up to 175% of maximum isometric force when muscles are stretched).
Stimulation Of Sodium Transport and Fluid Secretion by Ouabain in an Insect Malpighian Tubule
Authors: Maddrell S. H. P. , Overton J. A. 
Published: April 2021

ABSTRACT
Ouabain, at all concentrations higher than 2×l0−7mol l−1, stimulates the rate at which the Malpighian tubules of the insect, Rhodnius, transport sodium ions and fluid into the lumen. An effect on paracellular movement of sodium ions is unlikely because ouabain makes the electrical potential of the lumen more positive, which would slow diffusion of sodium into the lumen. Radioactive ouabain binds to the haemolymph-facing sides of the tubule cells but not to the luminal face. This binding is reduced in the presence of elevated levels of potassium or of non-radioactive ouabain. Bound ouabain is only slowly released on washing in ouabain-free saline. The evidence suggests that there is a Na+/K+-ATPase on the outer (serosal) membranes of the tubules. Such a pump would transport sodium in a direction opposed to the flow of ions and water involved in fluid transport; poisoning it with ouabain would remove this brake, and fluid flow and sodium transport would increase, as observed.
Effects of Hyposmotic Shock on Ion Fluxes in Isolated Trout Hepatocytes
Authors: Bianchini L. , Fossat B. , Porthé-Nibelle J. , Ellory J. C. , Lahlou B. 
Published: April 2021

ABSTRACT
Isolated trout hepatocytes exposed to hypotonic Hank’s medium (isotonicity × 0·70) swelled to 1·17 times the control volume after 3 min; by 15 min the cell volume had returned to normal.
The ouabain-insensitive K+ uptake increased, indicating an immediate rise in K+ membrane permeability. As indicated by analysis of cellular contents, the regulatory volume decrease (RVD) was ensured by a release of intracellular K+. Na+ was not implicated in this mechanism. This potassium permeability induced by hypotonic shock was transient (maximum at 6min), insensitive to blocking agents of voltage-and Ca2+-dependent K+ channels, and chloride-dependent.
This result, together with a time-course of Cl− uptake similar to that of K+, suggests a K+/C1− cotransport mechanism. This cotransport is inhibited by high furosemide concentrations (10−3mol l−1) but not by bumetanide (10−4mol l−1) or piretanide (10−4mol l−1).
Induction of Bioluminescence Capability in the Marine Fish, Porichthys Notatus, by Vargula (Crustacean) [14C]Luciferin and Unlabelled Analogues
Authors: Thompson Eric M. , Toya Yoshiaki , Nafpaktitis Basil G. , Goto Toshio , Tsuji Frederick I. 
Published: April 2021

ABSTRACT
Along the Pacific coast of North America, the marine fish, Porichthys notatus, is distributed as a northern nonluminescent population and a southern luminescent one. Bioluminescence capability is inducible in nonluminescent P. notatus by a single oral or intraperitoneal administration of a small amount of luciferin, a compound used by the marine ostracod crustacean, Vargula, as substrate for light emission. Once induced, the fish is capable of luminescing for more than 2 years. The results of the present study show that: (1) P. notatus photophores incorporate 14C-labelled Vargula luciferin: (2) the specific activity of the incorporated label is undiluted when recovered from the photophores 7 weeks later; (3) two chemical analogues of Vargula luciferin do not induce bioluminescence capability in the fish; (4) luciferinol, another close analogue of Vargula luciferin, induces a very weak bioluminescent capability in the fish; and (5) two key intermediates in the degradation of Vargula luciferin, oxyluciferin and etioluciferin, are ineffective in inducing bioluminescence capability. The conclusions to be drawn from this study are that P. notatus recycles luciferin and that, in the uninduced fish, the recycling does not involve the resynthesis of luciferin from oxyluciferin or etioluciferin.
Photoreceptor Potential Causing Phototaxis of Paramecium Bursaria
Authors: Matsuoka Kohji , Nakaoka Yasuo 
Published: April 2021

ABSTRACT
Paramecium bursaria shows phototaxis by accumulating in a lighted region. Intracellular recordings from both chlorella-containing and chlorella-free cells showed that a step-increase in the light intensity induced a steady depolarization of membrane potential, and a step-down caused recovery to the original level. The action spectrum of the depolarization corresponded to that for phototaxis, and showed two peaks at 420 and 560 nm. The amplitude of the depolarization became larger as light intensity was increased. Cells which accumulated in a lighted spot decreased their swimming velocity or stayed in the same place. As the light intensity was increased from dark, swimming velocity decreased and became zero at the intensity at which the cell showed the most noticeable photoaccumulation. Further increase in light intensity produced an increase in swimming velocity. The degree of photoaccumulation was inversely proportional to the swimming velocity. These results suggest that a step-increase in light intensity induces the steady depolarization and causes the decrease in swimming velocity, resulting in accumulation of cells in the lighted region.
Effect of Temperature Upon Carbon Dioxide Stores in the Snake Coluber Constrictor and the Turtle Chrysemys Scripta
Authors: Stinner Jerry N. , Wardle Robert L. 
Published: April 2021

ABSTRACT
The effect of temperature upon respiratory exchange ratio (R) was measured in snakes (Coluber constrictor) and turtles (Chrysemys scripta). Increasing body temperature produced a transient elevation of R, and lowering body temperature transiently depressed R. These thermal effects resulted from an ‘excess’ and a ‘deficit’ CO2 elimination, respectively. Steady-state blood CO2 content in C. constrictor decreased linearly with rising temperature. Plasma bicarbonate concentration, calculated from in vivo arterial and pH, followed the same pattern. Also, time courses of blood were consistent with the metabolic studies. Less than half of the change in blood could be explained by shifts of the in vitro CO2 dissociation curve; the remainder was contributed by other tissues. Blood lactate levels changed little with temperature. Based upon the blood studies, the predicted quantity of CO2 eliminated from the extracellular space when temperature increases is about 29% of the excess CO2 eliminated from the snakes. Thus, in other tissues also decreases with rising temperature. It is concluded that reptiles function as open systems with respect to , which does not agree with alphastat control. Systemic arterial and increased with rising body temperature in C. constrictor. The mechanisms producing these increases are discussed.
Freezing Avoidance and the Distribution of Antifreeze Glycopeptides in Body fluids and Tissues of Antarctic Fish
Authors: Ahlgren Jeffrey A. , Cheng Chi-Hing C. , Schrag Joseph D. , Devries Arthur L. 
Published: April 2021

ABSTRACTThe distribution of antifreeze glycopeptides (AFGPs) in the body fluids and tissues of antarctic notothenioid fish was determined. In Dissostichus mawsoni (Norman), the peritoneal, pericardial and extradural fluid, like the blood, contained all eight AFGPs and in concentrations sufficient to depress freezing points below that of sea water (−1·9°C). Secreted fluids including urine, endolymph and aqueous and vitreous humour either lack all AFGPs or have very low concentrations of only the low molecular weight forms and have freezing points of about −1·0°C, and are therefore undercooled with respect to environmental temperature.Fluids with high concentrations of AFGPs also contain high levels of proteins similar to plasma proteins. Systemic administration of tritiated AFGPs in the closely related species Trematomus bernacchii (Boulenger) yielded a distribution pattern similar to that of the native AFGPs in D. mawsoni. This suggests passive distribution of AFGPs into the various fluid compartments following secretion from the liver; a pattern typical of secreted blood proteins.Tissue distribution of AFGPs was determined by comparison with that of the extracellular space marker [14C]polyethylene glycol. AFGPs were found in the interstitial fluid of all body tissues examined except brain tissue. No tissue showed any intracellular accumulation of tritiated AFGPs from the blood.