bluuebunny/crossref_metadata_2025_split huggingface dataset:
Stimulus–Secretion Coupling in the Neurohypophysis of the Jerboa Jaculus Orientalis
Authors: Raji Aicha , Nordmann Jean J. 
Published: April 2021

ABSTRACT
In many mammals, severe dehydration is known to cause exhaustion of the vasopressin content of the neural lobe. Here, we have examined the physiological state of the neurohypophysis of the jerboa Jaculus orientalis, a rodent inhabitant of a semi-desert climate. Isolated neurohypophyses and neurosecretory nerve endings were perfused in vitro and vasopressin and oxytocin release were determined by radioimmunoassay. Electrical stimulation of the neurohypophysis with bursts of pulses mimicking the activity of hypersecreting neuroendocrine neurones induced similar increases of secretion in both control animals and animals dehydrated for up to 2 months. Neurohormone release was greatly potentiated when the bursts of pulses were separated by silent intervals. Prolonged stimulation of neurohypophyses from both control and dehydrated animals induced a sustained increase of vasopressin release; in contrast, oxytocin release under similar conditions showed a biphasic secretory pattern consisting of a transient increase that subsequently decreased to a steady level whose amplitude was similar to that for vasopressin. K+-induced secretion was largely inhibited by the Ca2+ channel blockers nicardipine and ω -conotoxin, suggesting that in this neurosecretory system both L-and N-type calcium channels play a major role in stimulus–secretion coupling. Depolarization of isolated nerve endings using a fast-flow perifusion system showed that there was no difference in the amplitude and the time course of the secretory response in dehydrated and hydrated animals. The results demonstrate that, despite the climatic conditions in which the jerboas live, their neural lobes retain the capacity to release, upon depolarization of the plasma membrane of the nerve endings, large amounts of neurohormone. It is concluded that the neurohypophyseal peptidergic release system in the dehydrated jerboa functions adequately even under extreme environmental stress.
Emperor Penguin Oxygen Consumption, Heart Rate and Plasma Lactate Levels During Graded Swimming Exercise
Authors: Kooyman G. L. , Ponganis P. J. 
Published: April 2021

ABSTRACT
Oxygen consumption , heart rate and blood chemistry were measured in four emperor penguins, Aptenodytes forsteri (Gray), during graded swimming exercise. The maximum obtained, 52 ml O2 kg−1 min−1, was 7.8 times the measured resting of 6.7 ml O2 kg−1 min−1 and 9.1 times the predicted resting . As the swimming effort rose, a linear increase in surface and submerged heart rates (fH) occurred. The highest average maximum surface and submersion heart rates of any bird were 213 and 210 beats min−1, respectively. No increase in plasma lactate concentrations occurred until was greater than 25 ml O2 kg−1 min−1. At the highest values measured, plasma lactate concentration reached 9.4 mmol l−1. In comparison with other animals of approximately the same mass, the aerobic capacity of the emperor penguin is less than those of the emu and dog but about the same as those of the seal, sea lion and domestic goat. For aquatic animals, a low aerobic capacity seems to be consistent with the needs of parsimonious oxygen utilization while breath-holding.
An Electrophysiological Survey of Frog Olfactory Cilia
Authors: Kleene Steven J. , Gesteland Robert C. , Bryant Shirley H. 
Published: April 2021

ABSTRACTIndividual olfactory receptor neurons vary widely in their responses to odorants. Olfactory stimulus reception occurs in the cilia of the receptor neurons. Thus, the variability among individual neurons could in part be due to differences among the olfactory cilia. We have quantified the known conductance properties of each of 117 frog olfactory cilia. From a strictly qualitative viewpoint, the cilia were very homogeneous. All but a few of them had a basal conductance in the absence of odorants and second messengers, conductances stimulated by cytoplasmic cyclic AMP and by Ca2+ and a conductance measured in the presence of ATP and stimulated by GTPγS. However, the magnitudes of the conductances varied widely among the cilia. Amplitudes of the cyclic-AMP-and Ca2+-activated ciliary currents correlated strongly with one another across the 117 cilia and 24 frogs studied, suggesting that expression of the underlying channels may be co-regulated. None of the conductance properties correlated strongly with ciliary length, a marker of cell maturity. Given cytoplasmic MgATP as substrate, ciliary adenylate cyclase apparently produced cyclic AMP, which in turn gated membrane channels and increased the ciliary conductance. In some cilia, MgATP alone caused a very large increase in conductance. In others, there was little effect unless GTPγS, which increases cyclase activity, was also added. No effect of cytoplasmic inositol trisphosphate on ciliary conductance was detectable.
Extracellular and Intracellular Carbon Dioxide Concentration as a Function of Temperature in the Toad Bufo Marinus
Authors: Stinner J. N. , Newlon D. L. , Heisler N. 
Published: April 2021

ABSTRACT
Previous studies of reptiles and amphibians have shown that changing the body temperature consistently produces transient changes in the respiratory exchange ratio (RE) and, hence, changes in whole-body CO2 stores, and that the extracellular fluid compartment contributes to the temperature-related changes in CO2 stores. The purpose of this study was to determine whether the intracellular fluid compartment contributes to the changes in CO2 stores in undisturbed resting cane toads. Increasing body temperature from 10 to 30°C temporarily elevated RE, and returning body temperature to 10°C temporarily lowered RE. The estimated average change in whole-body CO2 stores associated with the transient changes in RE was 1.0±0.8 mmol kg−1 (±S.D., N=6). Plasma [CO2] and, thus, extracellular fluid [CO2], were unaffected by the temperature change. Plasma calcium levels were also unaffected, so that bone CO2 stores did not contribute to changes in whole-body CO2 stores. Intracellular [CO2] was determined for the lung, oesophagus, stomach, small intestine, liver, ventricle, red blood cells, skin and 14 skeletal muscles. [CO2] was significantly lower (P&lt;0.05) at higher temperature in 10 of these, and seven others, although not statistically significant (P&gt;0.05), had mean values at least 0.5 mmol kg−1 lower at the higher temperature. The average change in intracellular [CO2] for all tissues examined was -0.165 mmol kg−1°C−1. We conclude that, in cane toads, the temperature-related transients in RE result from intracellular CO2 adjustments, that different tissues have unique intracellular CO2/temperature relationships, and that a combination of respiratory and ion-exchange mechanisms is used to adjust pH as temperature changes.
Motion-Sensitive Cells: Putative Larval Neurones Incorporated Into the Optic Lobe of the Adult Swallowtail Butterfly
Authors: Ichikawa Toshio 
Published: April 2021

ABSTRACT
Intracellular recordings were made from neurones with large somata situated at the anteromedial edge of the medulla of the swallowtail butterfly Papilio xuthus; the neurones were then filled with Lucifer Yellow. These cells are putative larval visual interneurones incorporated into the adult optic lobe of the butterfly. There are four classes of motion-sensitive neurones. Two have a dendritic arborization in the dorsal half of the medulla and project an axon to the medial protocerebrum or the contralateral medulla. They respond to vertical downward motion with a strong burst of action potentials and their background activities are inhibited by motion in the opposite direction. Variations in position of the dendritic fields suggest that each group of neurones forms a coherent set of cells detecting vertical motion in the dorsal half of the visual field of the eye. The third class of neurones connects the lobula plate to the midbrain and is preferentially sensitive to vertical upward motion. The fourth class of neurones has a dendritic arborization in the lobula. These neurones are tonically excited by a moving grating irrespective of the stimulus orientation and movement direction. The presence of motion-sensitive medulla neurones suggests that the detection of local motion is completed in the distal medulla.
y+-type cationic amino acid transport: expression and regulation of the mCAT genes
Authors: MacLeod Carol L. , Finley Kim D. , Kakuda Donald K. 
Published: April 2021

ABSTRACT
The transport of cationic amino acids across animal cell membranes is largely mediated by a small group of well-described transport systems (y+, bo,+, Bo,+). Only recently have genes encoding transport proteins in some of these systems been isolated. Two genes, mCAT-1 and mCAT-2, encode related multiple membrane-spanning proteins that share substantial amino acid sequence identity and virtually superimposable hydrophilicity profiles. mCAT-1 and mCAT-2 proteins expressed in Xenopus oocytes are functionally indistinguishable and similar to transport system y+, but have distinct tissue distribution patterns. mCAT-1 expression is nearly ubiquitious and produces a single protein, while mCAT-2 is highly tissue-specific, has two distinct protein isoforms encoded by a single gene and is expressed in different tissues using at least two widely separated promotors. All three proteins facilitate the ion-independent transport of arginine, lysine and ornithine. Both mCAT-1 and mCAT-2 proteins have low amino acid sequence similarity but strikingly similar hydrophilicity profiles with amino acid antiporters, uniporters and symporters of yeast, fungi and eubacteria. Current work will elucidate whether any of the mCAT proteins interact with members of a newly identified family of single membrane-spanning proteins, such as rBAT, 4F2 and NAA-Tr, which are thought to modulate or activate y+L and/or bo,+ transport systems.
Structure, Function and Evolution of Solute Transporters in Prokaryotes and Eukaryotes
Authors: Hediger Matthias A. 
Published: April 2021

ABSTRACT
In both prokaryotes and eukaryotes, transport systems of organic solutes can be classified as passive transporters, such as channels and facilitated transporters, and active transporters, which utilize diverse energy-coupling mechanisms. In the past decade, our understanding of the biochemistry and molecular biology of transporters from Escherichia coli has progressed significantly, whereas the analysis of mammalian transporters has initially been limited by the ability to purify membrane proteins. The recent development of methods to detect the activity of recombinant proteins in individual cells, however, has led to the cloning of several novel mammalian transporter cDNAs. One of the most useful expression cloning systems is Xenopus oocytes in conjunction with uptake studies and electrophysiological experiments. Overall, the sequence information and the functional data derived from many transporters has revealed unifying designs, similar energy-coupling mechanisms and common evolutionary origins. Here, I will provide a general survey of the known transport systems in bacteria, yeast, plants, insects and vertebrates and illustrate the different types of transport systems in mammals by discussing transporters recently studied in our laboratory.
‘Active’ Sugar Transport In Eukaryotes
Authors: Wright Cernest M. , Loo Donald D. F. , Panayotova-Heiermann Mariana , Lostao M. Pilar , Hirayama Bruce H. , Mackenzie Bryan , Boorer Kathyrn , Zampighi Guido 
Published: April 2021

ABSTRACT
Sugar transporters in prokaryotes and eukaryotes belong to a large family of membrane proteins containing 12 transmembrane alpha-helices. They are divided into two classes: one facilitative (uniporters) and the other concentrative (cotransporters or symporters). The concentrative transporters are energised by either H+ or Na+ gradients, which are generated and maintained by ion pumps. The facilitative and H+-driven sugar transporters belong to a gene family with a distinctive secondary structure profile. The Na+-driven transporters belong to a separate, small gene family with no homology at either the primary or secondary structural levels. It is likely that the Na+-and H+-driven sugar cotransporters share common transport mechanisms. To explore these mechanisms, we have expressed cloned eukaryote Na+/sugar cotransporters (SGLT) in Xenopus laevis oocytes and measured the kinetics of sugar transport using two-electrode voltage-clamp techniques. For SGLT1, we have developed a six-state ordered model that accounts for the experimental data. To test the model we have carried out the following experiments. (i) We measured pre-steady-state kinetics of SGLT1 using voltage-jump techniques. In the absence of sugar, SGLT1 exhibits transient carrier currents that reflect voltage-dependent conformational changes of the protein. Time constants for the carrier currents give estimates of rate constants for the conformational changes, and the charge movements, integrals of the transient currents, give estimates of the number and valence of SGLT1 proteins in the plasma membrane. Ultrastructural studies have confirmed these estimates of SGLT1 density. (ii) We have perturbed the kinetics of the cotransporter by site-directed mutagenesis of selected residues. For example, we have identified a charged residue which dramatically changes the kinetics of charge transfer. (iii) We have examined the kinetics of sugar and Na+ analogs. The Vmax of sugar transport decreases dramatically with bulky phenyl glucosides and increases when H+ replaces Na+. These results permit us to extend and refine our model for transport. The model has been useful in the analysis of mutant SGLT1 proteins: in the case of a D176A mutant, the primary effect is to alter rates of conformational changes of the unloaded protein, and with the glucose/galactose malabsorption syndrome mutant D28N SGLT1, the mutation disrupts the delivery of SGLT1 glycosylated protein from the endoplasmic reticulum to the plasma membrane.
Functional significance of the beta-subunit for heterodimeric P-type ATPases
Authors: Chow Dar C. , Forte John G. 
Published: April 2021

ABSTRACT
We have reviewed the structural and functional role of the β-subunit in a subfamily of the P-ATPases known as the α/ β-heterodimeric, cation-exchange ATPases. The subfamily consists of the various isoforms of Na+/K+-ATPase and H+/K+-ATPase, both of which pump a cation out of the cell (Na+ or H+, respectively) in recycle exchange for K+. Much of the earlier work has emphasized the functional activities of the α-subunit, which shares many characteristics with the broader P-ATPase family. It is now clear that the glycosylated β-subunit is an essential component of the cation-exchange ATPase subfamily. All β-subunit isoforms have three highly conserved disulfide bonds within the extracellular domain that serve to stabilize the α-subunit, α/ β interaction and functional activity of the holoenzyme. Evidence strongly suggests that the β-subunit is involved in the K+-dependent reactions of the enzymes, such as the E1-E2 transition and K+ occlusion, and that the extracellular domain of the β-subunit plays an important role in determining the kinetics of K+ interaction. In most vertebrate cells, the unassociated α-subunit is restricted to the endoplasmic reticulum (ER), and assembly of the complex occurs within the ER. Signals for exiting the ER and directing the correct intracellular trafficking are primarily determined by the β-subunit; Na+/K+-ATPase typically terminates in the plasma membrane facing the basolateral membrane, whereas all isoforms of H+/K+-ATPase terminate in the apical membrane. The C-terminal extracellular domain of the β-subunit is important for proper interaction with the α-subunit and for correct intracellular trafficking. Oligosaccharides on the β-subunit are not essential for enzyme function, but do serve to enhance the efficiency of α/ β association by increasing the lifetime of the unassociated β-subunit and the stability of the α/ β complex to tryptic attack. We propose that highly specialized glycosylation on the β-subunit of the gastric H+/K+-ATPase may help to protect that enzyme from the harsh extracellular environment of the stomach.
Evidence for Hydrodynamic Orientation by Spiny Lobsters in a Patch Reef Environment
Authors: Nevitt Gabrielle A. , Pentcheff N. Dean , Lohmann Kenneth J. , Zimmer-Faust Richard K. 
Published: April 2021

ABSTRACT
Western Atlantic spiny lobsters (Panulirus argus) are superb underwater navigators. Spiny lobsters perform dramatic seasonal offshore migrations and have also been shown to locate and home to specific den sites within the elaborate coral reef environment in which they live. How these animals perform such complex orientation tasks is not known. The study reported here was designed to explore the sensory mechanisms that spiny lobsters use to orient in and around a familiar patch reef environment. Our results show that, in the absence of visual cues, lobsters displaced a short (50 m) distance off the reef do not initially (i.e. within 20 min) travel towards their dens or return to the patch reef where their dens are located. Instead, the headings lobsters follow are significantly correlated to the direction of local hydrodynamic cues and, specifically, to the direction of approaching wave surge. Results from ultrasonic tracking experiments over longer periods (24 h) suggest that displaced lobsters are able to relocate the reef where they were captured, even without visual cues. These results suggest that hydrodynamic cues may provide useful and immediate directional information to lobsters within the local environment of the home reef.
Sodium-Dependent Norepinephrine-Induced Currents in Norepinephrine-Transporter-Transfected Hek-293 Cells Blocked by Cocaine and Antidepressants
Authors: Galli Aurelio , Defelice Louis J. , Duke Billie-Jeanne , Moore Kimberly R. , Blakely Randy D. 
Published: April 2021

ABSTRACT
Transport of norepinephrine (NE+) by cocaine- and antidepressant-sensitive transporters in presynaptic terminals is predicted to involve the cotransport of Na+ and Cl-, resulting in a net movement of charge per transport cycle. To explore the relationship between catecholamine transport and ion permeation through the NE transporter, we established a human norepinephrine transporter (hNET) cell line suitable for biochemical analysis and patch-clamp recording. Stable transfection of hNET cDNA into HEK-293 (human embryonic kidney) cells results in lines exhibiting (1) a high number of transporter copies per cell (106), as detected by radioligand binding and hNET-specific antibodies, (2) high-affinity, Na+-dependent transport of NE, and (3) inhibitor sensitivities similar to those of native membranes. Whole-cell voltage-clamp of hNET-293 cells reveals NE-induced, Na+-dependent currents blocked by antidepressants and cocaine that are absent in parental cells. In addition to NE-dependent currents, transfected cells possess an NE-independent mode of charge movement mediated by hNET. Hnet antagonists without effect in non-transfected cells abolish both NE-dependent and NE-independent modes of charge movement in transfected cells. The magnitude of NE-dependent currents in these cells exceeds the expectations of simple carrier models using previous estimates of transport rates. To explain our observations, we propose that hNETs function as ion-gated ligand channels with an indefinite stoichiometry relating ion flux to NE transport. In this view, external Na+ and NE bind to the transporter with finite affinities in a cooperative fashion. However, coupled transport may not predict the magnitude or the kinetics of the total current through the transporter. We propose instead that Na+ gates NE transport and also the parallel inward flux of an indeterminate number of ions through a channel-like pore.
The Development of Thermotolerance Protects Blowfly Flight Muscle Mitochondrial Function From Heat Damage
Authors: El-Wadawi Rukaya , Bowler Ken 
Published: April 2021

ABSTRACT
The LD50 of 10-day-old adult blowflies was determined to be 38.12±0.07 ˚C.
A transitory increase in heat resistance occurred following the exposure of adult blowflies to a sublethal heat shock at 36 ˚C. This thermotolerance was apparent 1 h after the application of the shock, was maximal 2–3 h later and had disappeared 6 h after exposure.
Oxidative phosphorylation by flight muscle mitochondria from control flies was impaired by an LD50 dose in vivo using both pyruvate+proline (P+P) and glycerol 3-phosphate (G3P) as substrates. Acceptor control (state III respiration/state IV respiration) was lost with G3P as substrate and so ADP:O ratios were not measurable.
The effect of experimental temperature in vitro on respiratory performance of mitochondria isolated from control and thermotolerant flies was also determined between 19 and 39 ˚C. State III respiration was markedly temperature-dependent in mitochondria from control flies with both substrates; it was maximal at 24–29 ˚C and fell progressively at higher measuring temperatures. In mitochondria from thermotolerant flies, state III respiration was less temperature-dependent with both substrates but this was most marked for G3P. The effect of experimental temperature on state IV respiration was similar in mitochondria from control and thermotolerant flies with each substrate, but differed between the two substrates. With G3P as substrate, respiration rate rose with temperature with a Q10 of approximately 1.5; however, with P+P as substrate, the trend was for respiration rate to fall as experimental temperature rose.
Using G3P as substrate, acceptor control was demonstrable at 34 ˚C in some preparations of mitochondria from thermotolerant flies but not in those from control flies at that temperature. With P+P as substrates, acceptor control was demonstrable in mitochondria from both control and thermotolerant flies at all experimental temperatures.
Distribution and action of SALMFamide neuropeptides in the starfish Asterias rubens
Authors: Elphick Maurice R. , Newman Suzanna J. , Thorndyke Michael C. 
Published: April 2021

ABSTRACT
The SALMFamides S1 and S2 are two structurally related neuropeptides that are present in starfish, and which share the C-terminal amino acid sequence SXLXFamide, where X is variable. To establish the distribution of S1 and S2 in starfish, we have raised antisera that recognise specifically the C-terminal pentapeptide sequence of either S1 or S2. Here we describe the production and characterisation of an S2-specific antiserum designated CLII. This antiserum, together with an S1-specific antiserum (BLII), has been used in a radioimmunoassay to measure S1 and S2 levels in extracts of body parts from the starfish Asterias rubens. High concentrations (250–400 pmol g-1) of both peptides were detected in the radial nerve cords of the nervous system and lower concentrations were detected in other body parts, including neuromuscular organs such as the tube feet, apical muscle and cardiac stomach. We have examined the pharmacological effects of S1 and S2 on the contractility of these three preparations. Neither S1 nor S2 influenced the tone of tube foot and apical muscle preparations but S2 caused relaxation of cardiac stomach preparations, antagonising the contracting action of acetylcholine.