bluuebunny/crossref_metadata_2025 huggingface dataset:
Excitation of Identified Serotonergic Neurons by Escape Command Neurons In Lobsters
Authors: Hörner Michael , Weiger Wendy A. , Edwards Donald H. , Kravitz Edward A.
Published: April 2021

Serotonin-containing neurosecretory neurons in the first abdominal ganglion (A1 5-HT cells) of the lobster (Homarus americanus) ventral nerve cord have been shown previously to function as ‘gain setters’ in postural, slow muscle, command neuron circuitries. Here we show that these same amine neurons receive excitatory input from lateral (LG) and medial (MG) giant axons, which are major interneurons in phasic, fast muscle systems. Activation of either LG or MG axons elicits short-latency, non-fatiguing, long-lasting excitatory postsynaptic potentials (EPSPs) in A1 5-HT cells which follow stimulus frequencies of up to 100 Hz in a 1:1 fashion. Single spikes triggered in either giant axon can produce EPSPs in the A1 5-HT cells of sufficient magnitude to cause the cells to spike and to fire additional action potentials after variable latencies; action potentials elicited in this way reset the endogenous spontaneous spiking rhythm of the A1 5-HT neurons. The giant-axon-evoked EPSP amplitudes show substantial variation from animal to animal. In individual preparations, the variation of EPSP size from stimulus to stimulus was small over the first 25 ms of the response, but increased considerably in the later, plateau phase of each response. When tested in the same preparation, EPSPs in A1 5-HT cells evoked by firing the LG axons were larger, longer-lasting and more variable than those triggered by firing the MGs. Firing A1 5-HT cells through an intracellular electrode, prior to activation of the giant fiber pathway, significantly reduced the size of LG-evoked EPSPs in A1 5-HT cells. Finally, morphological and physiological results suggest that similarities exist between giant fiber pathways in lobsters and crayfish. The possible functional significance of an involvement of these large amine-containing neurosecretory neurons in both tonic and phasic muscle circuitries will be discussed.
Slow Inhibition of Na+ Current in Crayfish Axons by 2-(1Non-8Enyl)-5-(1Non-8Enyl)Pyrrolidine (Pyr9), a Synthetic Derivative of an ant Venom Alkaloid
Authors: Lebrun Bruno , Cattaert Daniel
Published: April 2021

2,5-Dialkylpyrrolidines present in the venom of ants from the genus Monomorium are natural insecticides causing a flaccid paralysis. The mechanism of action of 2-(1non-8enyl)-5-(1non-8enyl)pyrrolidine (Pyr9), a synthetic derivative of 2,5-dialkylpyrrolidines, has been investigated in vitro on preparations of the ventral nerve cord of the crayfish Procambarus clarkii. Our results clearly indicate that Pyr9 blocks spike conduction without affecting the resting potential. Voltage-clamp experiments carried out on axons demonstrate that this blockade is due to a dual expression of Na+ current inhibition: a tonic inhibition developing slowly (90 % of inhibition within 20 min for a Pyr9 concentration of 50 μmol l−1) and independently of stimulation, and a phasic inhibition developing during repetitive stimulation (5 Hz), the accumulation kinetics of which is 0.072 pulse−1 at 5 Hz, according to the Courtney model. These findings suggest that tonic and phasic inhibition are due to different mechanisms. In addition, Pyr9 induces a shift of the Na+ inactivation curve towards more hyperpolarized potentials, which is in agreement with a higher affinity of Pyr9 for inactivated than for resting Na+ channels.
Evidence for Cholinergic Inhibitory and Serotonergic Excitatory Neuromuscular Transmission in the Heart of the Bivalve Mercenaria Mercenaria
Authors: Kuwasawa Kiyoaki , Hill Robert B.
Published: April 2021

The heart of Mercenaria mercenaria is innervated bilaterally at the atria. A pair of cardiac nerves arise as a branch of the cerebro-visceral connective and run to the posterior end of the junction between each atrium and its efferent branchial vessel. Innervation evidently spreads over the heart, since both inhibitory and excitatory junctional potentials (IJPs and EJPs) can be recorded from the atria, the atrio-ventricular (AV) valve or the ventricle. The cardiac nerves contain inhibitory and excitatory axons. Neural stimulation can cause increases in the frequency or amplitude of beating, depending on the strength and frequency of stimulation. Electrical stimulation of the nerves to the incurrent and excurrent siphons causes bradycardia or tachycardia even after cutting the cerebro-visceral connective at a site anterior to the origin of the cardiac nerves. This may indicate a reflex pathway involving neurons whose cell bodies are located in the visceral ganglion.

Neural depression of myocardial action potentials is mediated by discrete IJPs, which follow nerve stimuli one-to-one. IJPs can be recorded from the atria, the AV valve or the ventricle. A long-lasting hyperpolarization follows cessation of excitatory stimulation of the cardiac nerve.

IJPs may be produced by cholinergic nerves and are mediated primarily by Cl−. They are blocked by Mytolon and by d-tubocurarine (dTC), but not by methylxylocholine. In low-[Cl−] solution, IJPs are inverted into depolarizing junctional potentials, which are blocked by Mytolon and dTC.

Neurally induced tachycardia is mediated by discrete EJPs, which also follow stimuli applied to the cardiac nerve in a one-to-one manner. EJPs can be recorded from the atria, the AV valve and the ventricle.

The myocardium and the AV valve were excited by application of serotonin. EJPs recorded from these sites were reduced in amplitude by methysergide (1-methyl-d-lysergic acid butanolamide), suggesting that the EJPs may be serotonergic.

Just after entering the heart, at the posterior end of the junction with the efferent branchial vessel, the cardiac nerves contain thick processes which show serotonin-like immunoreactivity. These processes spread along the ramifications of the nerves, which extend to the atrium, the AV valve, the ventricle and even into the wall of the aorta.

This study provides direct electrophysiological evidence for serotonergic EJPs and cholinergic IJPs, plus immunocytochemical evidence for neural processes containing serotonin, in the myocardium.
Modulation of Attack Behavior and its Effect on Feeding Performance in a Trophic Generalist Fish, Hexagrammos Decagrammus
Authors: Nemeth Donna Henriques
Published: April 2021

This study examines the ability of a temperate marine fish, Hexagrammos decagrammus, to modulate its prey capture behavior in response to differences in prey type. This species has an extremely broad diet, feeding on prey which demonstrate very different anti-capture behaviors. Video-taped attacks on three shrimp species, one crab and pieces of shrimp were analyzed to determine the relative contributions of suction-feeding and ram-feeding behaviors to prey capture. The prey capture behaviors used by the predator were related to differences in escape behavior among the three shrimp species. H. decagrammus used behaviors characteristic of other ram-feeding predators when feeding on the two most elusive shrimp species: high attack velocity, attack initiated at a greater distance from the prey, and greater movement of the predator relative to the prey. Strikes at crabs and pieces of shrimp elicited strikes more typical of other suction-feeding predators, with lower attack velocities, shorter initial predator–prey distances and greater relative movement of the prey towards the predator. Attacks on the least elusive shrimp species showed elements of both ram and suction feeding. Modulation of attack velocity increased capture success on elusive prey, supporting the hypothesis that diet diversity is associated with the presence of a repertoire of feeding behaviors. These data suggest that functional differences in prey anti-capture behavior, as well as the functional versatility of the predator, must be addressed in ecomorphological studies that try to correlate predator morphology with diet.
Chloride Secretion Drives Urine Formation in Leech Nephridia
Authors: Zerbst-Boroffka Irene , Bazin Brita , Wenning Angela
Published: April 2021

The transport mechanisms underlying urine formation in leech nephridia were investigated in situ and in isolated preparations using pharmacological, electrophysiological and micropuncture techniques. Canalicular cells, which secrete the primary urine, function as a Cl--secreting epithelium. An apical Cl- conductance contributes to the lumen-negative potential which drives transcellular K+ transport and paracellular Na+ transport. On the basolateral side, a ouabain-sensitive Na+/K+-ATPase contributes substantially to the cellular and transcellular potential and provides the Na+ gradient necessary for a bumetanide-sensitive Na+/K+/2Cl- cotransport. Final urine is formed by subsequent reabsorption of ions along the central canal, where KCl and NaCl are reabsorbed in different portions.

The postprandial diuresis is not a consequence of the changes in blood osmolality or ion concentrations. Similar changes in the ionic environment do not promote diuresis in isolated nephridia. Apparently, the composition and volume of the primary urine cannot be separately controlled. Any increase in fluid secretion by leech canalicular cells involves upregulation of the paracellular pathway and stimulation of Cl- entry, which thereby changes the normally K+-enriched primary urine to the Na+-enriched primary urine characteristic of leeches in diuresis.
Developmental Changes in Chemoreceptive Control of Gill Ventilation in Larval Bullfrogs (Rana Catesbeiana) I. Reflex Ventilatory Responses to Ambient Hyperoxia, Hypoxia and Nacn
Authors: Jia XI XI , Burggren Warren W.
Published: April 2021

The time course of reflex changes in gill ventilation frequency, buccal pressure, branchial stroke volume and minute ventilation caused by a step-wise change in of inspired water and by the introduction of NaCN into the inspired water was measured in unanesthetized larval bullfrogs (Rana catesbeiana) at developmental stages TK V–VII, IX–XI and XVII–XIX. The inspiration of hypoxic or hyperoxic water caused significant increases in gill ventilation within 7 s, while hyperoxic water had the opposite effect. Introduction of NaCN into the inspired water stream caused nearly instantaneous respiratory responses (<3 s). Early and middle stage larvae showed a significantly faster and more pronounced reflex response than the older group in all experiments. The rapid changes in gill ventilation indicate the presence of a population of branchial receptors monitoring inspired water O2 levels or possibly blood O2 levels in the efferent branchial circulation. The progressive decrease in both the amplitude and rapidity of onset of the responses with development are consistent with the progressive degeneration of the gills and a reduction in the importance of branchial gas exchange in late larval stages.
Cellular Contraction Precedes Membrane Depolarization in Vorticella Convallaria
Authors: Shiono Hisashi , Naitoh Yutaka
Published: April 2021

Application of a mechanical stimulus to the cell body of the peritrich ciliate Vorticella convallaria evoked an all-or-nothing membrane depolarization, the large pulse. This was always accompanied by an all-or-nothing cellular contraction, and simultaneous recordings of the two events revealed that the large pulse was always preceded by the cellular contraction. A smaller graded membrane depolarization (the medium pulse) was sometimes produced in response to a weaker mechanical stimulus. The medium pulse was accompanied by a small, graded, localized contraction of the cell body and was occasionally followed by a large pulse. When a large pulse occurred during a medium pulse, it reached the same peak level as that of a large pulse evoked without a preceding medium pulse. When a medium pulse occurred during a medium pulse, summation of the two pulses was observed. Sustained contraction causes V. convallaria to become rounded, and in this state a mechanical stimulus stronger than that used to evoke the large pulse evoked a graded depolarizing mechanoreceptor potential in the cell. We conclude that both the large and medium pulses are caused by an inward receptor current that is activated mechanically following contraction of the cell body. A localized contraction evokes a small mechanoreceptor current, causing a medium pulse. An all-or-nothing contraction evokes a saturated, all-or-nothing mechanoreceptor current, causing a large pulse.
Experimental simulation of the thrust phases of fast-start swimming of fish
Authors: Ahlborn B. , Chapman S. , Stafford R. , Blake R. W. , Harper D. G.
Published: April 2021

Measurements of the thrust and forward impulse of a simulated fish tail and mathematical modeling indicate that the propulsive forces of fast-start swimming can be optimized by three different effects: (i) exactly inverting the tail tip vortex that is generated with the initial stroke, (ii) using a moderately flexible tail, and (iii) introducing a specific delay between the initial stroke and the return stroke. Experiments were performed with a new computer-controlled fish-tail simulation apparatus, and the results confirm the theoretical predictions of a previous study.
The interactive effects of feeding and exercise on oxygen consumption, swimming performance and protein usage in juvenile rainbow trout (Oncorhynchus mykiss)
Authors: Alsop Derek H. , Wood Chris M.
Published: April 2021

The impacts of feeding on the rate of O2 consumption aerobic swimming performance, nitrogenous waste excretion (ammonia-N and urea-N) and protein utilization as an aerobic fuel were investigated in juvenile rainbow trout. Feeding trout to satiation (in groups of 120) resulted in rapid growth and elevated routine by 68 % relative to fasted fish and by 30 % relative to trout fed a maintenance ration of 1 % of body mass daily. This in-tank of satiation-fed trout was approximately 70 % of the observed at the critical swimming speed (UCrit) when trials were performed on individual trout in swimming respirometers. Feeding increased at all swimming speeds; the absolute elevation (specific dynamic action or SDA effect) was dependent on ration but independent of swimming velocity. There was no difference in at UCrit amongst different ration treatments, but UCrit was significantly reduced by 15 % in satiation-fed fish relative to fasted fish. These results suggest that the irreducible SDA load reduces swimming performance and that is limited by the capacity to take up O2 at the gills and/or to deliver O2 through the circulatory system rather than by the capacity to consume O2 at the tissues. Ammonia-N and urea-N excretion increased with protein intake, resulting in a 6.5-fold elevation in absolute protein use and a fourfold elevation in percentage use of protein as an aerobic fuel for routine metabolism in satiation-fed trout (50–70 %) relative to fasted fish (15 %). Urea-N excretion increased greatly with swimming speed in all treatments, but remained a minor component of overall nitrogen excretion. However, even in satiation-fed fish, ammonia-N excretion remained constant as swimming speed increased, and protein did not become more important as a fuel source during exercise. These results suggest that the reliance on protein as a fuel is greatly dependent on feeding quantity (protein intake) and that protein is not a primary fuel for exercise as suggested by some previous studies.
Na+/H+ exchange and osmotic shrinkage in isolated trout hepatocytes
Authors: Fossat B. , Porthé-Nibelle J. , Pedersen S. , Lahlou B.
Published: April 2021

The ability of rainbow trout liver cells to regulate their intracellular pH (pHi) was studied using two methods on hepatocytes isolated by collagenase digestion: (i) by monitoring pHi with the fluorescent dye BCECF-AM, and (ii) by measuring the amiloride-sensitive uptake of 22Na, which represents Na+/H+ exchange. In low-Na+ medium (⩽ 16 mmol l−1), Na+ uptake was reduced by approximately 70 % in the presence of amiloride derivatives (DMA or MPA, 10−4 mol l−1).

Changing separately either the extracellular pH (pHe) or the intracellular pH (pHi, clamped by treating the cells with nigericin in the presence of 140 mmol l−1 K+) between 6 and 8 induced an increase in the rate of Na+ uptake when pHe was raised or when pHi was reduced.

When transferred to hypertonic medium, hepatocytes shrank to nearly 72 % of their initial volume, and thereafter a slow and partial regulatory volume increase phase was observed, with an increase in the amiloride-sensitive rate of Na+ uptake and an increase in intracellular pH. As DIDS-sensitive Cl− uptake was concomitantly enhanced, it is suggested that hypertonic stress activates Na+/H+ and Cl−/HCO3− exchange.
Transfer of the Heart Pacemaker During Juvenile Development in the Isopod Crustacean Ligia Exotica
Authors: Yamagishi Hiroshi , Hirose Euichi
Published: April 2021

Developmental changes in heartbeat pacemaker mechanisms were examined electrophysiologically in the isopod crustacean Ligia exotica. The heartbeat of embryos and early juveniles was myogenic. The heart muscle cells were coupled electrically, and no localized pacemaker activity was found in the heart. In newly hatched juveniles, the cardiac ganglion exhibited no spontaneous activity, although stimulation of the cardiac ganglion produced excitatory junctional potentials (EJPs) in the heart muscle. The myogenic activity of the heart was reset and entrained by the EJPs evoked by ganglionic stimulation. During juvenile development, spontaneous EJPs appeared irregularly in the heart muscle. Later in development, the cardiac ganglion started rhythmic bursting, and each muscle response followed a ganglionic burst discharge and overlapped the EJPs evoked by ganglionic activity. At this point, the activity of the cardiac ganglion was suppressed by application of tetrodotoxin (TTX); however, even in old adults, both muscle activity and the heartbeat continued following TTX application. Heartbeat frequency was lower in TTX-containing saline than in normal saline. These results show that, during juvenile development, the heart pacemaker is transferred from the heart muscle to the cardiac ganglion, which becomes the primary pacemaker and entrains the heart muscle activity to a higher frequency via EJPs.
The Influence of Proprioceptors Signalling Tibial Position and Movement on the Kick Motor Programme in the Locust
Authors: Jellema T. , Heitler W. J.
Published: April 2021

Four main proprioceptors monitor tibial position in the hindleg of the locust: the femoral chordotonal organ (FCO), the lump receptor, the suspensory ligament receptors and Brunner’s organ. The influence of these proprioceptors on quantitative aspects of the kick motor programme has been investigated. The parameters measured were the duration of the initial flexion burst, the duration of co-activation of flexor and fast extensor tibiae (FETi) motoneurones, the number of FETi spikes during the co-activation, the interval between the kick and post-kick flexion, the number of FETi spikes occurring in this interval and the duration of post-kick flexion activity. The lump receptor and Brunner’s organ have no detectable effect on any of these parameters. The FCO has highly significant effects on the duration of both initial flexion and post-kick flexion bursts, and on the number of FETi spikes occurring after the moment of tibial extension. The suspensory ligament receptors have significant effects upon the number of FETi spikes after the kick and the interval between the kick and the post-kick flexion. However, no proprioceptor had any influence upon the duration of co-activation or the number of FETi spikes during the co-activation. Thus, although elements of the kick motor programme preceding and following co-activation are strongly influenced by proprioceptors monitoring tibial position and movement, the co-activation stage, which is central to the effectiveness of the complete behaviour pattern, is not affected.
The Scaling and Potential Importance of Cutaneous and Branchial Surfaces in Respiratory Gas Exchange in Larval and Juvenile Walleye Stizostedion Vitreum
Authors: Rombough Peter J. , Moroz Brenda M.
Published: April 2021

Measurements were made of the surface areas (As) of the skin and gills of larval and juvenile walleye Stizostedion vitreum with a body mass (M) of between 2 mg (1 day post hatch) and 2.3 g (98 days post hatch). The skin, with a relative surface area (As/M) of approximately 8500 mm2 g−1, accounted for more than 99.9 % of the total surface area (skin + gills) at 1 day post hatch. The relative area of the skin decreased as fish grew at an allometric rate of b−1=−0.32±0.01 (mean ± S.E.M., where b−1 is the specific-mass exponent in the allometric equation Y×M−;1=aMb−;1, in which Y is surface area and a is a constant). The relative surface area of the gills (filaments + lamellae) increased in a hyperbolic fashion from very low levels (approximately 5 mm2 g−1) at 1 day post hatch to reach a maximum of approximately 1100 mm2 g−1 at a body mass of approximately 200 mg. Thereafter, relative gill area declined at an allometric rate of b−;1=−;0.19±0.10 (mean ± S.E.M.). Gill area, because it declined at a slower relative rate, finally exceeded skin area at a body mass of approximately 700 mg. The relative surface area of the skin and gills combined (total surface area) decreased at a more- or-less constant allometric rate of b−;1=−;0.21±0.01 (mean ± S.E.M.) throughout the experimental period. On the basis of the allometric rates of expansion, the structural capacity to supply oxygen (b−;1=−;0.19; total gill area, this study) and metabolic demand for oxygen (b−;1≈−;0.13; mean literature value for routine and resting metabolism) appear to remain fairly closely matched in postlarval walleye (>300 mg). The two parameters do not display the same degree of concordance during larval development. In larvae, total respiratory surface area declines on a mass-specific basis at roughly the same rate (b−;1=−;0.21) as gill area does in older fish but, unlike in older fish, metabolic demand for oxygen does not change (b−;1≈0.0). This results in a progr. essive decline in effective respiratory surface area (As/MO2) but does not affect O2 uptake, probably because larvae are so small that surface area is not the limiting factor in gas exchange. Analysis of data from the literature suggests that surface area typically becomes limiting at a body mass of approximately 100 mg. The major function of gills in smaller larvae (<100 mg) appears to involve ionoregulation or related aspects of acid–base balance rather than respiratory gas exchange.
Random Array of Colour Filters in the Eyes of Butterflies
Authors: Arikawa Kentaro , Stavenga Doekele G.
Published: April 2021

The compound eye of the Japanese yellow swallowtail butterfly Papilio xuthus is not uniform. In a combined histological, electrophysiological and optical study, we found that the eye of P. xuthus has at least three different types of ommatidia, in a random distribution. In each ommatidium, nine photoreceptors contribute microvilli to the rhabdom. The distal two-thirds of the rhabdom length is taken up by the rhabdomeres of photoreceptors R1–R4. The proximal third consists of rhabdomeres of photoreceptors R5–R8, except for the very basal part, to which photoreceptor R9 contributes. In all ommatidia, the R1 and R2 photoreceptors have a purple pigmentation positioned at the distal tip of the ommatidia. The R3–R8 photoreceptors in any one ommatidium all have either yellow or red pigmentation in the cell body, concentrated near the edge of the rhabdom. The ommatidia with red-pigmented R3–R8 are divided into two classes: one class contains an ultraviolet-fluorescing pigment. The different pigmentations are presumably intimately related to the various spectral types found previously in electrophysiological studies.
Control of Venom Production and Secretion by Sympathetic Outflow In The Snake Bothrops Jararaca
Authors: Yamanouye N. , Britto L. R. G. , Carneiro S. M. , Markus R. P.
Published: April 2021

Many studies have examined the morphological and biochemical changes in the secretory epithelium of snake venom glands after a bite or milking. However, the mechanisms of venom production and secretion are not yet well understood. The present study was undertaken to evaluate the role of the sympathetic nervous system in the control of venom production and secretion.

Venom glands were obtained from Bothrops jararaca (Viperidae) snakes, either unmilked previously or milked 4, 7 or 15 days before they were killed. Levels of tyrosine-hydroxylase-like immunoreactivity were higher in venom glands collected 4 days after milking, coinciding with the maximal synthetic activity of the secretory cells. The only catecholamine detected by high-performance liquid chromatography was noradrenaline, indicating the presence of noradrenergic fibres in these glands. In reserpine-treated milked snakes, no venom could be collected, and electron microscopic analysis showed narrow rough endoplasmic reticulum cisternae, instead of wide cisternae, and less well-developed Golgi apparatus compared with milked untreated snakes, indicating impairment of protein synthesis and secretion. The administration of isoprenaline or phenylephrine (β- and α-adrenoceptor agonists, respectively) to reserpine-treated milked snakes promoted the widening of the rough endoplasmic reticulum and restored venom production, but only phenylephrine restored the development of the Golgi apparatus and the formation of many secretory vesicles.

These results provide the first evidence that the sympathetic nervous system plays an important role in venom production and secretion in the venom glands of Bothrops jararaca. Understanding the importance of noradrenergic stimulation in venom production may provide new insights for research into the treatment of snakebites.
Reliability Of Continuous Tracer Infusion For Measuring Glucose Turnover Rate In Rainbow Trout
Authors: Haman François , Powell Mark , Weber Jean-Michel
Published: April 2021

Glucose plays a fundamental role in mammalian energetics but its contribution as a metabolic fuel is not well established for fish; the accurate in vivo measurement of glucose flux is essential to determine the importance of this substrate in the energy budget of teleosts. Therefore, the goal of the present study was to verify the reliability of the continuous tracer infusion method for estimating glucose turnover rate in rainbow trout Oncorhynchus mykiss. Our secondary goals were to determine whether glucose flux can be estimated more accurately from plasma or from whole-blood samples, and to obtain an estimate of renal glucose production. Continuous infusions of [6-3H]glucose were performed in hepatectomized and intact animals. In some hepatectomized individuals, liver glucose production was replaced by a pump infusing unlabelled glucose at a known rate. Renal glucose production was measured in hepatectomized fish where liver glucose production was not replaced, and it averaged 1.1±0.1 µmol kg−1 min−1 (mean ± S.E.M., N=5). Results show that glucose turnover rate is quantified accurately by continuous tracer infusion and that glucose flux can be estimated equally well from plasma (error of −0.7±4.9 %) and from whole-blood (error of −5.7±2.9 %) samples (means ± S.E.M., N=7). This study provides the first experimental validation of continuous tracer infusion in fish, and shows that this method could become a powerful tool to investigate hormonal regulation of glucose metabolism in live teleosts.
Coupling H+ Transport And Atp Synthesis In F1Fo-Atp Synthases: Glimpses Of Interacting Parts In A Dynamic Molecular Machine
Authors: Fillingame Robert H.
Published: April 2021

Reversible, F1Fo-type ATPases (also termed F-ATP synthases) catalyze the synthesis of ATP during oxidative phosphorylation. In animal cells, the enzyme traverses the inner mitochondrial membrane and uses the energy of an H+ electrochemical gradient, generated by electron transport, in coupling H+ translocation to ATP formation. Closely related enzymes are found in the plasma membrane of bacteria such as Escherichia coli, where the enzymes function reversibly depending upon nutritional circumstance. The F1Fo-type enzymes are more distantly related to a second family of H+-translocating ATPases, the vacuolar-type or V-ATPases. Recent structural information has provided important hints as to how these enzymes couple H+ transport to the chemical work of ATP synthesis. The simplest F1Fo-type enzymes, e.g. as in E. coli, are composed of eight types of subunits in an unusual stoichiometry of α3β3γδε (F1) and a1b2c12 (Fo). F1 extends from the membrane, with the α and β subunits alternating around a central subunit γ. ATP synthesis occurs alternately in different β subunits, the cooperative tight binding of ADP+Pi at one catalytic site being coupled to ATP release at a second. The differences in binding affinities appear to be caused by rotation of the γ subunit in the center of the α3β3 hexamer. The γ subunit traverses a 4.5 nm stalk connecting the catalytic subunits to the membrane-traversing Fo sector. Subunit c is the H+-translocating subunit of Fo. Protonation/deprotonation of Asp61 in the center of the membrane is coupled to structural changes in an extramembranous loop of subunit c which interacts with both the γ and ε subunits. Subunits γ and ε appear to move from one subunit c to another as ATP is synthesized. The torque of such movement is proposed to cause the rotation of γ within the α3β3 complex. Four protons are translocated for each ATP synthesized. The movement of γ and ε therefore probably involves a unit of four c subunits. The organization of subunits in Fo remains a mystery; it will have to be understood if we are to understand the mechanism of torque generation.
Regulation of proton-translocating V-ATPases
Authors: Merzendorfer Hans , Gräf Ralph , Huss Markus , Harvey William R. , Wieczorek Helmut
Published: April 2021

Vacuolar-type ATPases (V-ATPases) are proton-translocating enzymes that occur in the endomembranes of all eukaryotes and in the plasma membranes of many eukaryotes. They are multisubunit, heteromeric proteins composed of two structural domains, a peripheral, catalytic V1 domain and a membrane-spanning Vo domain. Both the multitude of locations and the heteromultimeric structure make it likely that the expression and the activity of V-ATPases are regulated in various ways. Regulation of gene expression encompasses control of transcription as well as control at the post-transcriptional level. Regulation of enzyme activity encompasses many diverse mechanisms such as disassembly/reassembly of V1 and Vo domains, oxidation of SH groups, control by activator and inhibitor proteins or by small signalling molecules, and sorting of the holoenzyme or its subunits to target membranes.
Regulation of Na+/Glucose Cotransporters
Authors: Wright Ernest M. , Hirsch Jochen R. , Loo Donald D. F. , Zampighi Guido A.
Published: April 2021

Na+/glucose cotransporters (SGLTs) are expressed in the small intestine and the proximal renal tubule, where they play a central role in the absorption of glucose and galactose from food and the reabsorption of glucose from the glomerular filtrate. The regulation of intestinal sugar absorption occurs over two distinct time scales, one over days and the other over minutes. This review focuses on the mechanisms involved in the shorter-term regulation. Recent studies of the mouse intestine in vitro demonstrated that Na+/glucose cotransport is increased two- to eightfold within minutes by the application of forskolin, an agent that increases intracellular cyclic AMP levels. Here we explore how cyclic AMP may upregulate Na+/glucose cotransport. Our strategy was to express cloned SGLT1s in Xenopus laevis oocytes and then use electrophysiological methods to measure (i) the kinetics of Na+/glucose cotransport, (ii) the number of cotransporters in the plasma membrane, and (iii) the net rate of exo- and endocytosis before and after activation of protein kinases. To evaluate the role of cotransporter phosphorylation, we have examined the effect of protein kinase activation on various SGLT1 isoforms and other cotransporters. In oocytes expressing rabbit SGLT1, the activation of protein kinase A (PKA) increased the maximum rate of Na+/glucose cotransport by 30 %, and the activation of protein kinase C (PKC) decreased the maximum rate of transport by 60 %. Changes in maximum transport rates were accompanied by proportional changes in the number of cotransporters in the plasma membrane and by changes in the area of the membrane. We conclude that PKA and PKC regulate rabbit SGLT1 activity by modulating the number of cotransporters in the plasma membrane and that this occurs through regulation of exocytosis and endocytosis. Given the size of intracellular transport vesicles containing SGLT1, 100–120 nm in diameter, and the density of cotransporters in these vesicles, 10–20 per vesicle, we estimate that the net rate of SGLT1 vesicle exocytosis is about 10 000 s−1 and that this rate increases 100-fold after activation of PKA. The effect of PKA is independent of the presence or absence of consensus sites for phosphorylation on SGLT1. Surprisingly, the effects of PKA or PKC depend critically on the sequence of the cotransporter being expressed in the oocyte, e.g. activation of PKC inhibited rabbit and rat SGLT1, but stimulated human SGLT1. This dependency suggests that the regulation of vesicle trafficking by protein kinases depends upon the structure of the cotransporter expressed in the oocyte. Similar considerations apply to other classes of cotransporters, such as the neurotransmitter and dipeptide cotransporters. Our working hypothesis is that the regulation of cotransporter expression by protein kinases occurs largely by regulated exo- and endocytosis, and that the effect of the protein kinases is indirect and determined by critical domains in the cotransporter.
Possible involvement of somatolactin in the regulation of plasma bicarbonate for the compensation of acidosis in rainbow trout
Authors: Kakizawa Sho , Ishimatsu Atsushi , Takeda Tatsusuke , Kaneko Toyoji , Hirano Tetsuya
Published: April 2021

Somatolactin is a putative pituitary hormone of the growth hormone/prolactin family in fish. Its function is still unknown. The effects of environmental hypercapnia and hypoxia, acid (HCl) infusion and exhaustive exercise on plasma somatolactin levels were examined in the chronically cannulated rainbow trout to study the possible physiological roles of somatolactin. Respiratory acidosis induced by hypercapnia (2 % CO2) did not affect plasma somatolactin level. In contrast, metabolic acidosis induced by acid infusion and exercise increased plasma somatolactin level. Blood pH was depressed to a similar extent by both types of acidosis, whereas plasma [HCO3−] was elevated by respiratory acidosis but reduced by metabolic acidosis. A moderate hypoxia (water 9.3 kPa) affected neither acid–base status nor plasma somatolactin level. A more severe hypoxia (water 6.1 kPa) resulted in metabolic acidosis accompanied by an apparent rise in plasma somatolactin level, although the difference in somatolactin level from the control value was not statistically significant. Somatolactin immunoneutralization retarded recovery of plasma [HCO3−] following acid infusion. These results indicate that somatolactin is involved in the retention of HCO3− during metabolic acidosis but not in the active accumulation of HCO3− for acid–base compensation of respiratory acidosis in rainbow trout Oncorhynchus mykiss.
Feeding mechanism and functional morphology of the jaws of the lemon shark Negaprion brevirostris (Chondrichthyes, Carcharhinidae)
Authors: Motta Philip J. , Tricas Timothy C. , Hueter Robert E. , Summers Adam P.
Published: April 2021

This study tests the hypothesis that preparatory, expansive, compressive and recovery phases of biting behavior known for aquatically feeding anamniotes are conserved among extant elasmobranch fishes. The feeding mechanism of the lemon shark Negaprion brevirostris is examined by anatomical dissection, electromyography and high-speed video analysis. Three types of feeding events are differentiated during feeding: (1) food ingestion primarily by ram feeding; (2) food manipulation; and (3) hydraulic transport of the food by suction. All feeding events are composed of the expansive, compressive and recovery phases common to aquatically feeding teleost fishes, salamanders and turtles. A preparatory phase is occasionally observed during ingestion bites, and there is no fast opening phase characteristic of some aquatically feeding vertebrates. During the compressive phase, palatoquadrate protrusion accounts for 26 % of the gape distance during jaw closure and is concurrent with muscle activity in the dorsal and ventral preorbitalis and the levator palatoquadrati. Hydraulic transport events are shorter in duration than ram ingestion bites. Prey ingestion, manipulation and hydraulic transport events are all found to have a common series of kinematic and motor components. Individual sharks are capable of varying the duration and to a lesser extent the onset of muscle activity and, consequently, can vary their biting behavior. We propose a model for the feeding mechanism in carcharhinid sharks, including upper jaw protrusion. This study represents the first electromyographic and kinematic analysis of the feeding mechanism and behavior of an elasmobranch.
Seasonal variation in uptake of short-chain neutral amino acid by red blood cells and hepatocytes in trout (Salmo trutta)
Authors: Gallardo M. A. , Canals P. , Albi J. L. , Pesquero J. , Sanchez J.
Published: April 2021

The present study shows that the capacity of trout (Salmo trutta) red blood cells (RBCs) and freshly isolated hepatocytes to take up short-chain neutral amino acids changes according to a seasonal pattern. Maximal amino acid uptake rates in RBCs were obtained in winter and spring, while minima were seen in summer and autumn. In contrast, the maximal rates for the freshly isolated hepatocytes were obtained in autumn and winter, and the minima were seen in spring and summer.

In addition, by studying the uptake of glycine, evidence was found that the activities of the amino acids carriers ASC, asc and Gly in RBCs varied according to a seasonal rhythm. The activity of the ASC and asc systems changed in parallel with the global uptake of amino acids.

Moreover, the RBC:plasma concentration ratio for certain substrates of these carriers (alanine, serine and glycine) varied accordingly. In contrast, the activity of the Gly system was modified inversely with respect to the overall amino acid uptake.

The activity of the ASC system in freshly isolated hepatocytes was also seasonally modified, reaching a maximum in autumn, shortly before the reproductive period.
The effects of exposure to ammonia on ammonia and taurine pools of the symbiotic clam Solemya reidi
Authors: Lee Raymond W. , Childress James J. , Desaulniers Nicole T.
Published: April 2021

The nutrition of the gutless clam Solemya reidi is supported by the activity of intracellular chemoautotrophic bacteria housed in its gill filaments. Ammonia (the sum of NH3 and NH4+) is utilized as a nitrogen source by the association and is abundant in the clam’s environment. In the present study, clams were exposed to 0.01–1.3 mmol l−1 ammonia for 22–23 h in the presence of thiosulfate as a sulfur substrate. Ammonia exposure increased the ammonia concentration in the tissue pools of the gill, foot and visceral mass from 0.5 to 2 μmol g−1 wet mass, without added ammonia, to as much as 12 μmol g−1 wet mass in the presence of 0.7 and 1.3 mmol l−1 external ammonia. Gill tissue ammonia concentrations were consistently higher than those in the foot and visceral mass. The elevation of tissue ammonia concentration compared with the medium may be due in part to an ammonia trapping mechanism resulting from a lower intracellular pH compared with sea water and greater permeability to NH3 compared with NH4+. Rates of ammonia incorporation into organic matter (assimilation) were determined using 15N as a tracer. 15N-labeled ammonia assimilation was higher in gill than in foot and increased as a function of 15N-labeled ammonia concentration in the medium. The size of the free amino acid (FAA) pool in the gill also increased as a function of ammonia concentration in the medium. This entire increase was accounted for by a single amino acid, taurine, which was the predominant FAA in both gill and foot tissue. Aspartate, glutamate, arginine and alanine were also abundant but their levels were not influenced by external ammonia concentration. Ammonia assimilation appeared to occur at rates sufficient to account for the observed increase in taurine level. These findings suggest that taurine is a major product of ammonia assimilation.
The Three-Dimensional Hydrodynamics of Tadpole Locomotion
Authors: Liu Hao , Wassersug Richard , Kawachi Keiji
Published: April 2021

Tadpoles are unusual among vertebrates in having a globose body with a laterally compressed tail abruptly appended to it. Compared with most teleost fishes, tadpoles swim awkwardly, with waves of relatively high amplitude at both the snout and tail tip. In the present study, we analyze tadpole propulsion using a three-dimensional (3D) computational fluid dynamic (CFD) model of undulatory locomotion that simulates viscous and unsteady flow around an oscillating body of arbitrary 3D geometry. We first confirm results from a previous two-dimensional (2D) study, which suggested that the characteristic shape of tadpoles was closely matched to their unusual kinematics. Specifically, our 3D results reveal that the shape and kinematics of tadpoles collectively produce a small ‘dead water’ zone between the head-body and tail during swimming precisely where tadpoles can and do grow hind limbs – without those limbs obstructing flow. We next use our CFD model to show that 3D hydrodynamic effects (cross flows) are largely constrained to a small region along the edge of the tail fin.

Although this 3D study confirms most of the results of the 2D study, it shows that propulsive (Froude) efficiency for tadpoles is overall lower than predicted from a 2D analysis. This low efficiency is not, however, a result of the high-amplitude undulations of the tadpole. This was demonstrated by forcing our ‘virtual’ tadpole to swim with fish-like kinematics, i.e. with lower-amplitude propulsive waves. That particular simulation yielded a much lower Froude efficiency, confirming that the large-amplitude lateral oscillations of the tadpole do, indeed, provide positive thrust.

This, we believe, is the first time that the unsteady flow generated by an undulating vertebrate has been realistically modelled in three dimensions. Our study demonstrates the feasibility of using 3D CFD methods to model the locomotion of other undulatory organisms.
Acute Regulation of Glucose Uptake in Cardiac Muscle of the American Eel Anguilla Rostrata
Authors: Rodnick Kenneth J. , Bailey John R. , West Jenny L. , Rideout Alison , Driedzic William R.
Published: April 2021

We investigated the effects of anoxia and contractile activity on glucose uptake and the intracellular location of hexokinase in cardiac muscle of the American eel Anguilla rostrata. Uptake of 2-deoxyglucose (2-DG) by ventricle strips at 15 °C was increased by 45 % by anoxia and by 85 % by contractile activity over basal conditions. The anoxia- and contraction-induced increase in basal 2-DG uptake was inhibited completely by 25 μmol l−1 cytochalasin B, suggesting that facilitated glucose transporters are involved. Maximal activity of hexokinase in whole homogenates (approximately 10 μmol min−1 g−1 tissue) was 200 times higher than the maximal rate of 2-DG uptake measured in vitro (46 nmol min−1 g−1 tissue). Only 20–25 % of hexokinase activity was localized to the mitochondrial fraction, and this was not altered by perfusion of the hearts with anoxic media. It is therefore unlikely that anoxia-induced stimulation of 2-DG uptake is mediated by intracellular translocation of hexokinase. As in the case of mammalian muscle, glucose 6-phosphate is a potent inhibitor of hexokinase in eel cardiac muscle (IC50=0.44 mmol l−1). In summary, anoxia and contractile activity significantly increase 2-DG uptake in cardiac muscle of American eels, and glucose transport may be rate-limiting for glucose utilization. Increased utilization of glucose during anoxia or contractile activity may involve the recruitment of facilitative glucose transport proteins to the cell surface of myocytes or an increase in the intrinsic activity of glucose transporters already residing at the cell surface.
METABOLIC IMPORTANCE OF Na+/K+-ATPase ACTIVITY DURING SEA URCHIN DEVELOPMENT
Authors: Leong P. K. K. , Manahan D. T.
Published: April 2021

Early stages of animal development have high mass-specific rates of metabolism. The biochemical processes that establish metabolic rate and how these processes change during development are not understood. In this study, changes in Na+/K+-ATPase activity (the sodium pump) and rate of oxygen consumption were measured during embryonic and early larval development for two species of sea urchin, Strongylocentrotus purpuratus and Lytechinus pictus. Total (in vitro) Na+/K+-ATPase activity increased during development and could potentially account for up to 77 % of larval oxygen consumption in Strongylocentrotus purpuratus (pluteus stage) and 80 % in Lytechinus pictus (prism stage). The critical issue was addressed of what percentage of total enzyme activity is physiologically active in living embryos and larvae and thus what percentage of metabolism is established by the activity of the sodium pump during development. Early developmental stages of sea urchins are ideal for understanding the in vivo metabolic importance of Na+/K+-ATPase because of their small size and high permeability to radioactive tracers (86Rb+) added to sea water. A comparison of total and in vivo Na+/K+-ATPase activities revealed that approximately half of the total activity was utilized in vivo. The remainder represented a functionally active reserve that was subject to regulation, as verified by stimulation of in vivo Na+/K+-ATPase activity in the presence of the ionophore monensin. In the presence of monensin, in vivo Na+/K+-ATPase activities in embryos of S. purpuratus increased to 94 % of the maximum enzyme activity measured in vitro. Stimulation of in vivo Na+/K+-ATPase activity was also observed in the presence of dissolved alanine, presumably due to the requirement to remove the additional intracellular Na+ that was cotransported with alanine from sea water. The metabolic cost of maintaining the ionic balance was found to be high, with this process alone accounting for 40 % of the metabolic rate of sea urchin larvae (based on the measured fraction of total Na+/K+-ATPase that is physiologically active in larvae of S. purpuratus). Ontogenetic changes in pump activity and environmentally induced regulation of reserve Na+/K+-ATPase activity are important factors that determine a major proportion of the metabolic costs of sea urchin development.
Fish Foot Prints: Morphology and Energetics of the Wake Behind a Continuously Swimming Mullet (Chelon Labrosus Risso)
Authors: Müller U. K. , Van Den Heuvel B. L. E. , Stamhuis E. J. , Videler J. J.
Published: April 2021

The structure of the wake behind a continuously swimming mullet was analysed qualitatively and quantitatively by applying two-dimensional particle image velocimetry. A detailed analysis of the flow pattern and of the swimming movements of the fish allowed us to derive a kinematic explanation of the flow pattern as well as an estimate of the relative contributions of the body and the tail to thrust production. During active propulsion, the undulatory swimming fish shed a wake consisting in the medio-frontal plane of a rearward, zigzagging jet flow between alternating vortices. The fish shed one vortex per half tailbeat when the tail reached its most lateral position. Part of the circulation shed in the vortices had been generated previously on the body by the transverse body wave travelling down the body. This undulatory pump mechanism accounted for less than half of the energy shed in the wake. The remainder was generated by the tail. The vortex spacing matched the tailbeat amplitude and the stride length.