bluuebunny/crossref_metadata_2025 huggingface dataset:
Angiotensin Converting Enzyme in Brush-Border Membranes of Avian Small Intestine
Authors: Stevens Bruce R. , Fernandez Alarico , Del Rio Carlos Martinez
Published: April 2021

Angiotensin converting enzyme activity was identified in brush-border membranes purified from the small intestinal epithelium of the common grackle, Quiscalus quiscula. Angiotensin converting enzyme was enriched 20-fold in the membrane preparation, compared with intestinal epithelial cell scrapes, and was coenriched with the brush-border markers, alkaline phosphatase and aminopeptidase N. The kinetics of hydrolysis of N-[3-(2-furyl)acryloyl]-L-phenylalanylglycylglycine (FAPGG) gave a Vmax of 907 ± 41 units g−1 and a Km of 55 ± 6μmol I−1. The avian intestinal angiotensin converting enzyme was inhibited by the antihypertensive drug, Ramipril, with a median inhibitory concentration (IC50) of 1 nmol I−1. In the light of previous studies on angiotensin converting enzyme in mammalian epithelia, these results may implicate a physiological role for angiotensin converting enzyme in regulating electrolyte and fluid uptake in bird small intestines.
Changes In Electrical Connection During Cell Fusion In The Heliozoan, Echinosphaerium Akamae
Authors: Nishi Takako , Gotow Tsukasa , Kobayashi Makoto
Published: April 2021

The electrophysiology of cell fusion in the heliozoan, Echinosphaerium akamae, was studied by intracellular recording from two unicellular organisms undergoing fusion. Fusion was preceded by the electrical connection of axopodia of each cell to the cell body of the other. In the early stages of the fusion process, spikes evoked in one cell body failed to invade the other, but electrotonic potentials (subthreshold depolarizations) did pass to the other cell. When background depolarizing currents were injected into the organism into which the potentials had invaded, these potentials developed into spikes. In advanced stages of fusion, spikes were transmitted in both directions from one organism to the other, in the absence of polarizing current. At this time, application of appropriate hyperpolarizing currents to either of the two organisms prevented spikes produced in one from invading the other. These results suggest that in the early stage of fusion, relatively few axopodia were bridged by membrane fusion between paired cell bodies, and that the number of such bridged axopodia increased as fusion proceeded, allowing spikes to be transmitted between the two organisms.
Effects Of Acid-Base Variables On in vitro Hepatic Metabolism In Rainbow Trout
Authors: Walsh Patrick J. , Mommsen Thomas P. , Thomas W. Moon , Steve F. Perry
Published: April 2021

The effects of hypercapnia (1 % CO2), and the independent effects of changes in extracellular pH (pHe), and [HCO3−] on intracellular pH (measured by the DMO method) and lactate metabolism (measured by utilization of 14C-labelled lactate), were examined in rainbow trout hepatocytes in vitro. Simulated uncompensated hypercapnia (high , low pHe, moderately increased [HCO3−] led to a substantial depression in the production of CO2 (44%) and glucose (51%) from lactate. In simulated compensated hypercapnia (high normal pHe, high [HCO3−], metabolism was still significantly inhibited (18–33%). Subsequent multifactorial design experiments determined that variations in , pH and [HCO3−] independently affected metabolism; increased and decreased pH inhibited metabolism, but increased [HCO3−] stimulated metabolism. These results are interpreted in terms of the effects of acid-base variables on enzymatic and transport pathways, and the possible causes of decreased hepatic glycogen stores during in vivo hypercapnia are discussed.
Perfusion-Independent Oxygen Extraction in Myoglobin-Rich Hearts
Authors: Bailey John R. , Driedzic William R.
Published: April 2021

Cardiac myoglobin plays a role in oxygen consumption and has a protective effect during periods of hypoxia, but little is known about the role of myoglobin during periods of ischaemia. Myoglobin-rich sea raven hearts and myoglobin-poor ocean pout hearts were isolated and perfused at varying flow rates and under conditions of low and high oxygen demand to assess the role of myoglobin in oxygen extraction. In the myoglobin-rich hearts, oxygen extraction remained constant over the flow range. In the myoglobin-poor hearts, oxygen extraction was significantly elevated, relative to controls, at the lower flow rates but decreased as the flow rate increased. In hearts where myoglobin was inactivated by an oxidizing agent, oxygen extraction was similar to that observed in myoglobin-poor hearts. Under conditions of high oxygen demand, myoglobin-rich hearts again showed a constant oxygen extraction over the flow range. Myoglobin-inactivated hearts had a significantly elevated oxygen extraction at low flows, and this decreased as flow rate increased. These data suggest that myoglobin renders oxygen extraction by fish hearts independent of the rate of perfusion.
Hair Cell Mechanoreception in the Jellyfish Aglantha Digitale
Authors: Arkett S. A. , Mackie G. O. , Meech R. W.
Published: April 2021

The jellyfish Aglantha digitale is equipped with clusters of hair cells on the velum and on the tentacle bases. The cells have a central non-motile cilium surrounded by a collar of microvilli. The microvilli are graded in length, from long on one side to short on the other, giving the collar a marked polarity. The hair cells are set in specific orientations in all regions where they occur, as shown by this polarity. Small mechanical displacements of the velum or tentacles in the vicinity of the hair cells evoke bursts of potentials which can be recorded extracellularly from the outer nerve ring. Intracellular recordings from the ring giant axon, which is implicated in escape locomotion, show patterns of facilitating EPSPs correlated with these potentials. Hair cell input may be important in feeding as well as in locomotory behaviour. Three classes of hair cells were studied : those of the tentacle bases (T cells) and those of the velum (C cells and F cells). Direct stimulation of the tentacle bases shows that the T cells respond to slight mechanical displacements. To distinguish the functions of the C cells and F cells, which lie close together, a laser was used to ablate selectively one or other kind. It was found that the C cells respond to small mechanical displacements of the velum but no response could be assigned to the F cells.
Serotonergic Modulation of Patterned Motor Output in Lymnaea Stagnalis
Authors: Tuersley M. D. , McCROHAN C. R.
Published: April 2021

Rhythmic feeding motor output from the buccal ganglia of Lymnaea stagnalis was evoked by tonic depolarization of the pattern-initiating interneurone SO in the isolated central nervous system.

Perfusion with 10–4moll–1 serotonin (5-HT) led to a reduction in frequency of the SO-driven rhythm, and in some cases rhythmic activity was completely blocked. The frequency reduction was predominantly due to an increase in duration of the ‘inactive’ phase of the rhythm. In a number of preparations, the normal buccal rhythm was replaced by an ‘atypical’ pattern of bursting in buccal motoneurones in the presence of 5-HT. This was characterized by the absence of one phase (N2) of interneuronal activity in the feeding pattern generator.

Stimulation of the serotonergic giant cerebral interneurones (CGCs), to increase the mean spike frequency from 10 to 2-5 Hz, mimicked some of the effects of 5-HT perfusion. However, the timing of onset of CGC stimulation in relation to depolarization of SO was critical; prolonged activation of a CGC led to an apparent decrease in its effectiveness in suppressing the buccal rhythm.
Correlation Between Damping Coefficients and Externally Injected Currents in Oscillations Produced by Lithium ions in Frog Skin
Authors: Baptista Carlos Alberto , Ramos Margarida Perestrello , De Jesus Carlos Henriques
Published: April 2021

Oscillations in the electrical parameters elicited by Li+ added to the mucosal side of frog skin in vitro were studied under different experimental conditions.

The correlation between the damping coefficient and the size of the externally injected current was ascertained. The size of the overall epithelial resistance in NaCl-Ringer seems to be a good indicator of the qualitative behaviour of the skin in the presence of Li+: the higher the resistance the less probable the occurrence of oscillations.

Addition of amiloride allowed the calculation of the electromotive force in Na+-and Li+-Ringer.

Calculations of the ‘total equivalent inductance’ and ‘total equivalent capacitance’ of an oscillating skin were made using resistance values (R), damping coefficients (σ) and frequency of oscillation (ω).
Parallel Antiport Mechanisms for Na+ and Cl– Transport in Herbivorous Teleost Intestine
Authors: Howard James N. , Ahearn Gregory A.
Published: April 2021

Transport mechanisms for NaCl in intestinal brush border membrane vesicles (BBMV) of herbivorous, seawater-adapted tilapia, Oreochromis mossambicus, were investigated with a rapid filtration technique using 22Na+ and 36C1− as tracers. Evidence to support the existence of cotransport mechanisms (Na+/Cl– or Na+/K+/2Cr) in tilapia intestinal BBMV was not found. An inwardly directed Cl gradient or KCl gradient did not stimulate the uptake of Na+ into tilapia intestinal BBMV. Furthermore, the uptake of Na+ under these conditions was not significantly affected by furosemide. Evidence was found to indicate the existence of Na+/H+ and C1−/HCO3– antiport mechanisms for NaCl transport in tilapia intestinal BBMV. An outwardly directed proton gradient (pH 6·0 in, pH 7·5 out) stimulated the uptake of Na+ above that of the control (pH 7·5 in, pH 7·5 out). Exogenous amiloride (1 mmol 1−1) significantly reduced Na+ uptake in the presence of an outwardly directed proton gradient. Apparent influxes of 1 mmol 1−1 Na+ were (nmol mg protein–1 15 s–1± 1 S.E.) : control, 1·46 ± 0·09; pH gradient, 3·36 ± 0·14; pH gradient plus amiloride, 1·55±0·05. The uptake of Cl– was stimulated by outwardly directed HCO3– and Cl– gradients in comparison with an outwardly directed gluconate gradient. Apparent influxes of 10 mmol 1−’Cl– were (nmol mg protein–1 15s–1 ± 1 s.E.): gluconate, 12·90±0·19; HCO3–, 15·83±0·34; Cl–, 14·62 ± 0·42. These results suggest that, in contrast to the cotransport mechanisms for NaCl that have been reported for other fish intestine, the herbivorous marine teleost, Oreochromis mossambicus, possesses dual antiport mechanisms for the transport of NaCl across its intestinal brush border membrane.
Short-Chain Fatty Acid Transport in the Intestine of A Herbivorous Teleost
Authors: Titus Eric , Ahearn Gregory A.
Published: April 2021

Short-chain fatty acid (SCFA) concentrations of intestinal contents from the herbivorous tilapia, Oreochromis mossambicus, were analysed by gas and high-performance liquid chromatography. Concentrations of acetate ranging from 3 to 18 mmol I−1 were found along the full length of the intestinal tract, as were trace amounts of propionate. Characteristics of [3H]acetate transport by the intestinal brush-border membrane were analysed in isolated brush-border membrane vesicles (BBMV). Influx of [3H]acetate into BBMV occurred by apparent anion exchange and was not enhanced by inwardly directed gradients of sodium or potassium, indicating the lack of sodium-dependent coupling for acetate transport. Competition and stimulation studies with various organic and inorganic anions revealed the likelihood of a transport system in which [3H] acetate is exchanged specifically for intracellular bicarbonate or other SCFA. Other anions tested had only limited or negligible effects on [3H]acetate uptake. Kinetic analysis over a concentration range of external acetate from 0·1 to 35 mmol I−1 yielded a carrier transport Km of 6·4mmoll−1 and a Jmax of 5·3 nmol mg protein−1 10s−1. Transport of [3H]acetate was not significantly affected by inhibitory drugs specific for anion exchangers. This study suggests that there is a specific antiport system for anions that is shared by bicarbonate and short-chain volatile fatty acids in the intestinal brush-border membrane of this herbivorous teleost.
Effects of Ions on Nematocysts Isolated From Acontia of the Sea Anemone Caluactis Tricolor by Different Methods
Authors: Hidaka Michio , Mariscal Richard N.
Published: April 2021

Differences in nematocyst isolating procedures significantly affected the discharge characteristics of the acontial nematocysts isolated from Calliactis tricolor. Most of the nematocysts isolated in artificial sea water (ASW) discharged instantaneously in 5 mmol 1-1 EGTA and to a lesser degree in distilled water (DW), but they did not discharge in Ca2+-free ASW or 50 mmol 1-1 CaCl2. Most of the nematocysts isolated in lmoll-1 sodium citrate discharged instantaneously when treated with any of the above solutions. Nematocysts isolated in DW or 1 mol 1-1 sucrose exhibited a modest degree of discharge in 5mmoll-1 EGTA after a considerable latent period. Some of the present results appear to be inconsistent with the hypothesis that removal of Ca2+ from the intracapsular fluid causes nematocyst discharge.
Branchial Na+/K+-Atpase and Osmoregulation in the Isopod, Idotea Wosnesenskii
Authors: Holliday Charles W.
Published: April 2021

Pleopod Na+/K+-ATPase enzyme specific activity (ESA) and osmoregulatory performance were measured in isopods acclimated for 12-14 days in 100 %, 75 %, 50 % and 25 % sea water (SW). The animal was 63-65 mosmol kg–1 hyperosmotic to the medium in 100 % and 75 % SW, 214 mosmol kg–1 hyperosmotic in 50 % SW and 239 mosmol kg–1 hyperosmotic in 25% SW. The five pairs of pleopods are biramous but are not similar. The two anterior pairs do not stain with silver, have low and unchanging ESA, are smaller and more rigid than the three posterior pairs and are used for swimming. The posterior three pairs are thinner and more flexible; their endopodites stain with silver and have fivefold higher ESA than their exopodites or the front two pleopods. Only the endopodites of the posterior three pleopods showed large (twofold) increases in ESA in animals acclimated in dilute media. The time course of acclimation from 100% to 50% SW was measured: osmotic equilibrium occurred after 1 day; posterior endopodite ESA was elevated after 1 day and was fully activated after 3 days. Ablation of the endopodites of the posterior three pleopods eliminated the animal’s ability to hyperosmoregulate in 50% SW; ablation of the exopodites of the same append-ages or of both rami of the first two pairs of pleopods had no significant effect on osmoregulation. Thus, the endopodites of the posterior three pleopods of /. wosnesenskii are the sites of inward ion transport in dilute media.
The Aerobic Cost of Saltatory Locomotion in the Fowler’s Toad (Bufo Woodhousei Fowleri)
Authors: Walton Michael , Anderson Bruce D.
Published: April 2021

Studies of kangaroos suggest that hopping provides energy savings during locomotion at high speeds, although studies of small mammals suggest that hopping is no more economical than running. To obtain comparative data on anurans, we exercised Fowler’s toads (Bufo woodhousei fowleri, 25·8 g) on treadmills at speeds ranging from 0·09 to 0·63 km h−1 while measuring oxygen consumption , endurance or hop kinematics. The toads walked at slow speeds and hopped at fast speeds. Steady-state increased linearly with speed to a maximum of 1·17mlO2g−1h−1 at 0·27kmh−1 and was nine times the average pre-exercise . The maximum rate of oxygen consumption during treadmill exercise was comparable to previously reported for less natural exercise regimes. At speeds ⩾0·27 kmh−1, was independent of speed. At speeds ⩽0·36 kmh−1, toads moved for over 1h, but endurance decreased sharply at higher speeds. Hop rate, hop length, hop height and angle of take-off increased with speed. Hopping in B. w. fowleri was not less costly than running in other animals of similar body size and was inefficient at converting metabolic to mechanical energy. The present study suggests that hopping in toads, as in small mammals, is not economical during sustained locomotion and is most important during short bursts of high-intensity activity.
Effects of External Acidification on the Blood Acid-Base Status and Ion Concentrations of Lamprey
Authors: Mattsoff Leona , Nikinmaa Mikko
Published: April 2021

We studied the effects of acute external acidification on the acid-base status and plasma and red cell ion concentrations of lampreys. Mortality was observed within 24 h at pH5 and especially at pH4. The main reason for the high sensitivity of lampreys to acid water appears to be the large drop in blood pH: 0·6 and 0·8 units after 24 h at pH5 and pH4, respectively. The drop of plasma pH is much larger than in teleost fishes exposed to similar pH values. The difference in the plasma pH response between lampreys and teleosts probably results from the low buffering capacity of lamprey blood, since red cells cannot participate in buffering extracellular acid loads. Acidification also caused a decrease in both Na+ and Cl− concentrations and an elevation in K+ concentration of plasma. The drop in plasma Na+ concentration occurred faster than the drop in plasma Cl− concentration which, in turn, coincided with the decrease in total CO2 concentration of the blood.
Functional Characterization of A Voltage-Gated Anion Channel from Teleost Fish Intestinal Epithelium
Authors: Loretz Christopher A. , Fourtner Charles R.
Published: April 2021

An anion channel was isolated, using patch-clamp technique, from the basolateral membrane of goby intestinal epithelial cells. Single-channel conductance varied over a range from 20 to 90 pS. The channel was voltage-gated over the physiological range of cell membrane potential with depolarization increasing the proportion of time in the open state. There was no Ca2+ sensitivity. The selectivity sequence was SO42− > Cl− > Mes−.

The channel may function in vivo as one of several avenues of basolateral membrane Cl− exit with the voltage-gating property serving to match basolateral Cl−exit to apical entry.
Control of Cercal Position During Flight in the Cockroach: A Mechanism for Regulating Sensory Feedback
Authors: Libersat Frederic , Camhi Jeffrey M.
Published: April 2021

In a flying cockroach, the response of cereal wind receptors to standard wind stimuli was reduced by 40 % compared with when the animal was at rest. While flying, rhythmic bursts of action potentials, phase-locked to the wingbeat rhythm, descended the nerve cord. These bursts appeared responsible for a phase-locked rhythmic discharge of cereal motor neurones. This, in turn, evoked a cereal displacement, maintained throughout flight. It is suggested that this displacement causes a pressure block of the sensory nerve, since it has recently been shown that experimental displacement of the cercus in a non-flying cockroach causes a similar degree of sensory reduction (40%) by means of such a mechanism (Libersat, Goldstein & Camhi, 1987). The functional significance of this means of sensory reduction is discussed.
The Effect of Breathing Oxygen and Air on Diving Bradycardia in Cormorants (Phalacrocorax Auritus)
Authors: Jones David R. , Larigakis S.
Published: April 2021

Cardiovascular chemoreceptors are crucial for the development of forced diving responses in dabbling ducks such as the mallard (Anas platyrhynchos). Denervation of the peripheral chemoreceptors or allowing the duck to breath 100 % oxygen before a forced dive eliminates or considerably delays the onset of noticeable bradycardia (Jones & Purves, 1970; Mangalam & Jones, 1984). These procedures have no effect on the level of bradycardia established after 10 s or so underwater in diving ducks or cormorants in forced dives (Butler & Woakes, 1982; Mangalam & Jones, 1984; Furilla & Jones, 1986). The afferent neural pathway for the dive response is unclear in cormorants, but in diving ducks it is the stimulation of nasal receptors with water that causes dive bradycardia (Furilla & Jones, 1986). When forced dives are prolonged, then peripheral chemoreceptors appear to affect heart rate in diving ducks. Heart rate is elevated in ducks (Aythya fuligula) in which the carotid body has been denervated, compared with intact ducks, after 50 s or so of forced submergence (Butler & Woakes, 1982). The purpose of the present study was to investigate whether chemoreflexes also influence heart rate in cormorants in forced dives of up to 120s duration.
Radular Kinetics During Grazing in Helisoma Trivolvis (Gastropoda: Pulmonata)
Authors: Smith David A.
Published: April 2021

Three models for radular feeding in gastropod molluscs have been proposed: (1) odontophoral licking, where the radula is fixed to, and is directed by, a dynamic cartilage; (2) rope-and-pulley rasping, where the radula is dynamic and slides over a static cartilage; and (3) moving-conveyor-belt rasping, which involves independent though concurrent movements both of the radula and of the underlying cartilage. The implications of these alternative mechanical processes with regard to machine efficiency and to feeding optimality are considered. During radular feeding, individual Helisoma trivolvis (Say) employ the model which affords optimality both of food excavation and of food transport. Results showed that the radula of this species slides over the underlying cartilage while the cartilage independently accelerates across the substrate during each effective feeding stroke. Relative velocities (of the ribbon and of the odontophoral cartilage, VR: VO) ranged from 0·67:1 to 0·92:1 and these values were positively correlated with food availability.
Electrical Properties and Anion Permeability of Doubly Rectifying Junctions in the Leech Central Nervous System
Authors: Acklin Susan E.
Published: April 2021

A study has been made of the electrical connections between touch sensory (T) neurones in the leech central nervous system (CNS) which display remarkable double rectification: depolarization spreads in both directions although hyperpolarization spreads poorly. Tests were made to determine whether this double rectification was a property of the junctions themselves or whether it resulted from changes in the length constants of processes intervening between the cell body and the junctions. Following trains of action potentials, T cells and their fine processes within the neuropile became hyperpolarized through the activity of an electrogenic sodium pump. When any T cell was hyperpolarized by 25 mV by repetitive stimulation, hyperpolarization failed to spread to the T cells to which it was electrically coupled. Further evidence for double rectification of junctions linking T cells was provided by experiments in which Cl− was injected electrophoretically. Cl− injection into one T cell caused inhibitory potentials recorded in it to become reversed. After a delay, Cl− spread to reverse IPSPs in the coupled T cell. Movement of Cl−, like current flow, was dependent on membrane potential. When the T cell into which Cl− was injected was kept hyperpolarized, Cl− failed to move into the adjacent T cell. Upon release of the hyperpolarization in the injected T cell, Cl− moved and reversed IPSPs in the coupled T cell. Together these results indicate that the gating properties of channels linking T cells are voltage-dependent, such that depolarization of either cell allows channels to open whereas hyperpolarization causes them to close.
Involvement of the Terminal Abdominal Ganglion in Neuroendocrine Regulation of Integumentary Water Loss in the Cockroach Periplaneta Americana L
Authors: Noble-Nesbitt John , Al-Shukur Marwan
Published: April 2021

Neuroendocrine secretions from the terminal abdominal ganglion (TAG) augment the cephalic neuroendocrine regulation of integumentary water loss in the cockroach. As with the cephalic system, the TAG produces both promoting (TAGP) and restricting (TAGR) secretions which, respectively, lead to an increase or a decrease in the rate of integumentary water loss. The promoting factor (TAGP) requires priming by the cephalic promoting factor (BHP) before it is activated, and it probably acts by stimulating release of more BHP which in turn increases water loss through the integument. The restricting factor (TAGR) is autoactive and exerts its effects even in the absence of the cephalic neuroendocrine system or its secretions. It provides additional, independent restriction of integumentary water loss in adverse (desiccating) ambient conditions. Its action accounts for the longer-term decrease in water loss found in decapitated cockroaches.

These effects parallel closely the effects of the diuretic and antidiuretic hormones produced by the TAG. Measurement of faecal product demonstrates that the changes in overall water loss are not primarily due to changes in excretory loss but are due to regulation of integumentary permeability.
Barium and Calcium Block Bacillus Thuringiensis Subspecies Kurstaki δ-Endotoxin Inhibition of Potassium Current Across Isolated Midgut of Larval Manduca Sexta
Authors: Crawford Dwight N. , Harvey William R.
Published: April 2021

Ba2+ and Ca2+ prevent and reverse the Btk δ-endotoxin inhibition of the short-circuit current in isolated lepidopteran midgut. These findings support the K+ pump–leak steady-state model for midgut K+ homeostasis and the K+ channel mechanism of Bt toxin action. They provide a new tool with which to study the interactions between Bt toxin and midgut cell membranes.
The Importance of Nervous and Humoral Mechanisms in the Control of Cardiac Performance in the Atlantic Cod Gadus Morhua at Rest and During Non-Exhaustive Exercise
Authors: Axelsson Michael
Published: April 2021

The nervous regulation of heart rate and stroke volume in the Atlantic cod Gadus morhua was investigated both in vivo, during rest and exercise, and in vitro. The cholinergic and adrenergic influences on the heart were estimated in experiments with injections of atropine and sotalol. At rest the cholinergic and adrenergic tonus on the heart were 38% and 21%, respectively (ratio 1·81:1). At the end of an exercise period, the cholinergic tonus had decreased to 15% but the adrenergic tonus had increased to 28% (ratio 0·54:1). The results suggest that variation of the cholinergic tonus on the heart is a major factor in the regulation of the heart rate.

In one group of fish, cardiac output was also measured, allowing calculation of stroke volume. Cardiac output increased significantly during exercise, and this effect persisted in the presence of both atropine and sotalol, although the increase in heart rate was reduced or abolished. The persisting increase in cardiac output during exercise is due to an increase in stroke volume, reflecting a Starling relationship.

In the presence of the adrenergic neurone-blocking agent bretylium, a positive inotropic effect on isolated, paced atrial and ventricular strips was observed. In the atrial preparations the effect persisted after 24 h. The effect was prevented by pretreatment with sotalol or cocaine, but potentiated by phentolamine pretreatment. This shows that bretylium exerts its neurone-blocking action after being taken up into the adrenergic nerves, and suggests that the positive inotropic effect of bretylium observed in vivo is due to release of endogenous catecholamines.

The concentration-response curves for adrenaline on isolated spontaneously beating atrial preparations showed that the concentrations of catecholamines necessary to produce appreciable effects on the heart are higher than the concentrations found in cod plasma during ‘stress’ situations (handling and exhaustive swimming).
Modulation of Ionic Currents by Synaptic Action and 5-Ht Application in the Identified Heart Excitatory Neurone of the African Giant Snail, Achatina Fulica Férussac
Authors: Furukawa Yasuo , Kobayashi Makoto
Published: April 2021

In the African giant snail, Achatina fulica Férussac, the ionic mechanisms underlying slow depolarization of a heart excitatory neurone, PON, induced by the activity of two cerebral ganglionic neurones, d-RCDN and d-LCDN, were investigated under voltage-clamp.

The slow depolarization of PON that was induced by the activity of the cerebral neurones was blocked by the serotonin (5-HT) antagonist, methysergide. Bath application of 5-HT to the axotomized PON produced a similar slow depolarization, which was also blocked by methysergide. These results suggest that the neurotransmitter of d-RCDN and d-LCDN is 5-HT.

Under voltage-clamp, activity of the cerebral neurones usually produced an inward shift in the holding current of PON with a decrease of conductance. Ionic substitution experiments and injection of Cs+ into PON showed that the response was mainly due to a decrease in K+ conductance. In some cases, this inward shift showed two components: an early component with increased conductance and a late one with decreased conductance. The early component was not decreased by Cs+ injection but was augmented by EGTA injection into PON, which may suggest the involvement of a Ca2+ conductance in this synaptic response.

Application of 5-HT produced a similar inward shift in holding current which was also mainly the result of a decrease in the background K+ current. 5-HT was also found to increase the voltage-dependent Ca2+ current and the inward rectifying K+ current.

The significance of these results is discussed in relation to the heart regulation of this snail.
Visually Guided Chases in Polyphemus Pediculus
Authors: Young Stephen , Taylor Victoria A.
Published: April 2021

Polyphemus chases were video-recorded in a laboratory tank, and the positions and orientations of the chaser and target were digitized at 100-ms intervals. Analysis of the resulting track reveals three main phases: chaser pauses, shadowing prey at a constant distance, and rapid leaps onto prey. Chases do not all end in contact – they are sometimes terminated by the chaser peeling off. Pauses are triggered by rapid image expansions, and persist for as long as the image continues to expand. The shadowing phase includes intermittent sudden forward movements, which could provide visual information about the absolute size of the prey, using a triangulation method. Chasers are successful in avoiding contact with very large and very small prey.
Chasing with a Model Eye
Authors: Young Stephen
Published: April 2021

A simulation model for Polyphemus eye movements was based on an openloop saccadic control system, derived from previous observations of eye movements in response to sinusoidally oscillating targets. The model was checked against new observations of Polyphemus eye movements in response to erratically moving targets. It was used to predict eye movements in response to stimulus patterns deduced from an analysis of video-recordings of Polyphemus chases. The results show that the system is limited to tracking slow target movements, but that this is consistent with observed chasing behaviour.
Switch From Metabolic to Ventilatory Compensation of Extracellular pH in Crayfish
Authors: Burtin B. , Massabuau J.-C.
Published: April 2021

The mechanisms of extracellular pH regulation were studied in crayfish Astacus leptodactylus under conditions that were either favourable or unfavourable for ionoregulation. Animals in intermoult or premoult stages were kept in normoxic artificial waters at 13°C. In intermoult, acid–base balance (ABB) and ionoregulatory disturbances were induced by increasing the ambient partial pressure of CO2, by decreasing the concentration of NaCl in the water ([NaCl]w) or by associating both changes. In premoult we took advantage of the spontaneously occurring endogenous problems of ionoregulation which are linked to shell shedding.

In intermoult, an increase of , alone induced a hypercapnic acidosis compensated by metabolic means, whereas in association with a decrease of [NaCl]w (which induced a decrease of [NaCl] in the haemolymph) it led to a ventilatory compensation. In intermoult a decrease of [NaCl]w alone induced a metabolic acidosis that was compensated by metabolic means, whereas in premoult it was compensated by ventilatory adjustments.

It is concluded that when water breathers are facing experimentally induced or spontaneous ionoregulatory problems, compensation for superimposed ABB disturbances can be made by ventilatory adjustments instead of by metabolic means.
Time Course of the Establishment of Uterine Seawater Conditions in Late-Term Pregnant Spiny Dogfish (Squalus Acanthias)
Authors: Kormanik Gregg A.
Published: April 2021

The gestation period for embryos of the spiny dogfish, Squalus acanthias (L.) lasts for nearly 2 years. During the latter part of this period the pups remain in the uterus and the fluid surrounding the embryos resembles sea water with respect to the major ions, but is low in pH (approx. 6), high in partial pressure of carbon dioxide (approx. 3 mmHg; 1 mmHg = 133·3 Pa), low in total carbon dioxide content (approx. 0·2 mmol 1−1), and may have a total ammonia concentration of up to 22 mmol l−1. Thus the conditions under which the pups complete their development in utero is quite remarkable.

The derivation of these conditions was examined in late-term pregnant females, from whose uterine horns the pups had been removed, by monitoring changes that occurred in instilled uterine sea water. The mother is responsible for reducing the pH, reducing the total carbon dioxide content and elevating the partial pressure of carbon dioxide to the levels observed in fresh-caught females, in less than 24h. The ammonia concentration is also elevated, but this takes rather longer. The decreased pH is responsible for the accumulation of ammonia in the uterine sea water, and it also serves to protect the pups from the toxic effects of NH3, by converting it to the relatively non-toxic ionic form, NH4+. The reasons for the establishment of these uterine seawater conditions are still not evident.
Effect of Adrenaline and Blood Gas Conditions on Red Cell Volume and Intra-Erythrocytic Electrolytes in the Carp, Cyprinus Carpio
Authors: Fuchs D. A. , Albers C.
Published: April 2021

Carp, when subjected to air stress in vivo, developed a hypoxaemia associated with an acidosis due to elevation of and arterial lactate content. Adrenaline and noradrenaline levels rose markedly, and the mean corpuscular haemoglobin concentration (MCHC in mmol Hb l−1 red blood cells) decreased, indicating swelling of the erythrocytes. No effect of adrenaline could be observed in vitro after equilibration at normal pH and oxygenation level. Simulation of air stress in vitro, by using hypercapnic hypoxia together with adrenaline, caused appreciable swelling of the red cells. The effect of adrenaline could be blocked by propranolol and was reversible when the blood gases were readjusted to normal values. Swelling due to hypercapnic hypoxia was not affected by propranolol. At normal , lowering pH by increasing or adding HC1 to the blood at (l mmHg = 133·3 Pa) both led to swelling of red cells; further swelling occurred when adrenaline was added. At normal or even elevated intracellular pH, hypoxia led to red cell swelling; further swelling occurred when adrenaline was added. The swelling of red cells under hypoxic and/or acidotic conditions (induced by either added HC1 or increased ) was associated with an increase in the intracellular K+, Na+ and Cl− levels, together with an increase in the Donnan distribution ratio of Cl−, rCl. ΔK+: ΔNa+ was 4:1. The swelling associated with the addition of adrenaline was also accompanied by an increase in K+, Na+, Cl− aud rCl. In this case the ratio ΔK+: ΔNa+ was 1:2.4. There was a correlation between the Donnan ratio, rCl, and the change in MCHC, even in those cases where extracellular and intracellular pH were above normal. In addition to pH and oxygen saturation, rCl should therefore be considered as a possible triggering factor for the action of adrenaline. In addition to the increased catecholamine levels, stress during sampling may be inferred if low values of MCHC and high values of intraerythrocytic chloride and a high chloride distribution ratio, rCl, are found in whole blood.
The Rapid Tail Withdrawal Reflex of the Tubificid Worm, Branchiura Sowerbyi
Authors: Zoran Mark J. , Drewes Charles D.
Published: April 2021

The rapid tail withdrawal of the tubificid worm, Branchiura sowerbyi, was studied using correlated electrophysiological and behavioural analyses. The minimal response latency (i.e. time from onset of mechanical stimulus to onset of withdrawal) was approximately 7 ms, faster than the escape responses of any previously studied invertebrate. Factors contributing to the speed and efficacy of this response include: (1) a sensitive mechanosensory system for detecting potential prey, (2) a short latency for excitation along afferent and efferent pathways, (3) a rapid intersegmental conduction of lateral giant fibre spikes, (4) a short coupling time from muscle excitation to the onset of shortening, and (5) the requirement of only a single lateral giant fibre spike for a complete (all-or-none) response. Videotaped sequences of predator-prey interactions showed that such reflex speed permits effective escape from the strike of the bluegill (Lepomis macrochirus)
Protein Synthesis in a Fish Heart: Responses to Increased Power Output
Authors: Houlihan D. F. , Agnisola C. , Lyndon A. R. , Gray C. , Hamilton N. M.
Published: April 2021

The effects of exercise on the rates of protein synthesis in the chambers of the trout heart were investigated in vitro and in vivo. An in vitro rainbow trout heart preparation was developed which permitted perfusion of the coronary supply to the compact region of the ventricular muscle. This preparation was used to examine the mechanical responses to preload pressures, the oxygen consumption at different power outputs and the rates of protein synthesis in the various heart components. By increasing preload pressure it was possible to double cardiac output, oxygen consumption and power output without changing heart rate. Mechanical efficiency of the hearts was approximately 20%. Perfusion of the coronary vessels improved cardiac output. Protein synthesis was measured in isolated hearts by the incorporation of [3H]phenylalanine added at high concentration (1·35 mmol l−1) to the perfusion medium. The various chambers of the heart showed marked differences in their rates of protein synthesis. Increasing cardiac output and power output in vitro by twofold over 20 min increased the fractional rate of protein synthesis by approximately 2·5-fold in the atrium and ventricle but did not affect the rates in the bulbus arteriosus. Perfusion of the coronary vessels significantly increased the rates of protein synthesis of the compact layer of the ventricle. In vivo there were no significant differences in the fractional protein synthesis rates between the atrium and ventricle; slow-speed continuous swimming over 40 min (1·5 body lengths s−1) caused an increase in the rates of protein synthesis in all the chambers except the bulbus arteriosus. The stimulation in the fractional rates of protein synthesis by approximately 32% was not as great as in vitro. Both in vivo and in vitro the increased rates of protein synthesis occurred without any change in RNA to protein ratios, indicating an improved activity of protein synthesis per unit of RNA. It is concluded that shortterm increases in cardiac contractility, possibly acting through the mechanical stretch on the cardiac muscle, stimulated protein synthesis, particularly in the ventricle, through increased ribosomal activity.
Water Depth Alters Respiratory Behaviour of Xenopus Laevis
Authors: Shannon Patrick , Kramer Donald L.
Published: April 2021

Most studies of the control of air breathing in bimodally respiring aquatic animals neglect the influence of depth of dive. However, changes in respiratory patterns with depth may be expected on a number of grounds. Increased hydrostatic pressure will alter gas tensions in the lungs or accessory respiratory organs and may therefore increase the rate and degree of oxygen uptake (Butler & Jones, 1982). Changes in buoyancy may affect swimming energetics (Wassersug & Feder, 1983) or induce a compensatory rise in the amount of gas held during the dive (Graham, Gee, Motta & Rubinoff, 1987). The increased energetic cost of surfacing associated with greater distance may increase oxygen demand (Pandian & Vivekanandan, 1976). Finally, theories of optimal foraging applied to breathing suggest that animals diving to greater depths should load more oxygen at each trip to the surface, stay submerged longer, and increase reliance on dissolved oxygen (Kramer, 1988). Empirical evidence for effects of water depth on air breathing in fish and tadpoles is briefly reviewed by Bevan & Kramer (1987).
Lophotoxin Blocks Synaptic Acetylcholine Receptors in the Cockroach Periplaneta Americana
Authors: Blagburn Jonathan M. , Sattelle David B
Published: April 2021

The actions of lophotoxin on synaptic acetylcholine receptors were investigated, using the cholinergic synapse between the lateral filiform hair sensory neurone and giant interneurone 3 in the first-instar cockroach Periplaneta americana. Lophotoxin (1·0×10−6mol l−1) blocked transmission without affecting the passive or active membrane properties of the pre- and postsynaptic neurones, and without affecting non-cholinergic synaptic inputs. Micromolar concentrations of lophotoxin also blocked the depolarizing response of giant interneurone 3 to carbamylcholine, when applied ionophoretically to its dendritic branches. The toxin shifted the dose-response curve to the right by two orders of magnitude, suggesting that it was acting as a competitive antagonist.
In vivo Analysis of Partitioning of Cardiac Output Between Systemic and Central Venous Sinus Circuits In Rainbow Trout: A New Approach Using Chronic Cannulation of the Branchial Vein
Authors: Ishimatsu Atsushi , Iwama George K. , Heisler Norbert
Published: April 2021

Freshwater-acclimated rainbow trout were chronically and non-occlusively cannulated in the dorsal aorta (DA), sinus venosus (SV) and branchial vein (BV), the latter returning the blood perfusing the central venous sinus (CVS) of the gill after being shunted away from the systemic circuit. After recovery, blood samples from these three sites were analysed for haematocrit (Het) and [Hb]. Branchial venous blood was found to have considerably lower Hct and [Hb] (Het = 3·5 ± 3·1%; [Hb] = 1·04 ± 0·75g 100 ml−1) than systemic blood (DA: Hct = 24·3 ± 8·9%, [Hb] = 6·54 ± 2·90 g 100 ml−1; SV: Hct = 23·1 ± 8·8%, [Hb] = 6·15 ±2·55 g 100 ml−1; means ±S.D. N = 8), which strongly suggests that plasma skimming occurred at arteriovenous anastomoses and arterioles draining into the CVS. The partitioning of cardiac output, calculated on the basis of the [Hb] data, showed that the systemic flow accounted for 93 ± 4·6% (N = 7) of the total cardiac output with only 7 ± 4·7% of cardiac output being diverted into the CVS, thus bypassing the systemic vasculature. Previous results using in vitro experiments are compared with the present data in an evaluation of the usefulness of the isolated perfused gill and head preparations in the experimental analysis of circulatory physiology in fish gills.
Intracellular Calcium Translocation: Mechanism of Activation by Guanine Nucleotides and Inositol Phosphates
Authors: Gill Donald L. , Mullaney Julienne M. , Ghosh Tarun K.
Published: April 2021

The movements of Ca2+ within cells in response to external stimuli are complex. Internal Ca2+ release activated by inositol 1,4,5-trisphosphate (InsP3) is now widely established. However, the mechanism of InsP3-induced Ca2+ release, the identity and control of the InsP3-sensitive Ca2+ pool and its relationship to other internal and external Ca2+ pools all remain uncertain. We have characterized a highly sensitive and specific guanine nucleotide-regulatory mechanism that induces rapid and profound movements of intracellular Ca2+via a mechanism distinct from that activated by InsP3. Using permeabilized neural or smooth muscle cells, application of submicromolar concentrations of GTP induces rapid release of Ca2+ from a compartment that contains within it the InsP3-releasable Ca2+ pool. Although of similar GTP-sensitivity as G-protein-activated events, the apparent dependence on GTP hydrolysis and blockade by GTPγS suggest a mechanism distinct from those mediated by known G-proteins. Recent experiments in the presence of oxalate reveal rapid and profound GTP-activated uptake of Ca2+via a mechanism with identical nucleotide sensitivity and specificity to GTP-induced Ca2+ release. These results were interpreted to suggest that GTP induces a transmembrane conveyance of Ca2+ between different compartments distinguished by oxalate permeability; GTP-induced release probably occurs via a similar mechanism except involving transfer between closed compartments and nonclosed membranes (perhaps the plasma membrane). Recently, it has been revealed that GTP activates a translocation of Ca2+ into the Ca2+ pool from which InsP3 induces release. This is an important observation suggesting that the GTP-activated Ca2+ translocation process may control entry into and hence the size of the InsP3-releasable Ca2+ pool. Indeed, it is possible that GTP-induced Ca2+ release observed in permeabilized cells reflects a reversal of the pathway that functions in intact cells to permit external Ca2+ entry into the InsP3-releasable pool. This type of process could mediate the longer-term secretory or excitatory responses to external receptors which are known to be dependent on external Ca2+.
The Somatotrope: an Endocrine Cell With Functional Calcium Transients
Authors: Thorner Michael O. , Holl Reinhard W. , Leong Denis A.
Published: April 2021

Growth hormone (GH) secretion by the somatotrope is under dual regulation by the hypothalamic peptides, somatostatin (SS) and GH-releasing hormone (GHRH). Cytosolic free calcium concentration and cumulative GH release were measured simultaneously in anterior pituitary cells from adult male rats. This was made possible using a combination of digital imaging video microscopy with the fluorescent calcium indicator Fura-2 and the reverse haemolytic plaque assay (RHPA) to identify the cell type and measure hormone secretion from the cells under study. This technique allows calcium measurements to be made at very short time intervals (<150 ms) in single cells. Spontaneous calcium transients were demonstrated in 85% of GH plaque-forming cells. These occurred at a frequency of 2–13 min−1 and had an amplitude of 50–500 nmol l−1. The somatotropes with the largest calcium fluctuations produced the largest plaques; thus, the calcium transients appeared to correlate with hormone release. Since the somatotrope alone shows these fluctuations, the mean intracellular calcium concentration is 238 ±18 nmol l−1 in somatotropes and 113±8nmoll−1 in non-somatotropes. Upon exposure to SS (1 nmol l−1) intracellular calcium fell from 200–250 nmol I−1 to 50–100 nmol l−1 with an apparent reduction in oscillations. Withdrawal of SS increased the intracellular calcium level. GHRH increased intracellular calcium but 10nmoll−1 GHRH given simultaneously with Inmoll−1 SS reduced intracellular calcium to that level observed during SS alone. Thus, the SS effect on intracellular calcium predominates. The effects of SS can be mimicked by removal of extracellular calcium, or by the addition of CoCl2 (2 nmol l−1) or by verapamil (lOOfzmol l−1), two agents which block calcium channels.

The hormone secretion index (indicated by the area of the plaque formed in RHPA) enables us to demonstrate that GHRH in this system increases GH secretion, and SS inhibits it. In combination, GHRH and SS oppose one another.

Spontaneous calcium oscillations are characteristic for normal somatotropes. These oscillations are related to spontaneous hormone secretion and due to influx of calcium through ion channels in the membrane. Intracellular signalling information may be encoded in both frequency and amplitude of calcium oscillations. The actions of GHRH and SS on regulation of GH secretion are proposed to be mediated, at least in part, by regulation of intracellular cytosolic free calcium. This modulation is dependent on extracellular calcium concentrations. We are now investigating the molecular mechanisms involved in this process.