bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effects of Raised [K+]o And [Ca2+]o on Conjugation and on Electrophysiological Parameters in the Marine Ciliate Euplotes Vannus
Authors: Lueken W. , Krüppel T. , Gaertner M. 
Published: April 2021

ABSTRACT
Co-stimulation of mixed complementary mating types of Euplotes vannus was blocked if [K+]o was raised to at least 60 mmol l−1. This inhibition could be cancelled by simultaneously raising [Ca2+]o. An electrophysiological investigation showed that elevation of either [K+]o or [Ca2+]o depolarized the cell. The effect of potassium was observed at concentrations above 50 mmol l−1, with a slope of about 38 mV/decade change, and was accompanied by a reduction in membrane resistance. Calcium had an effect at lower concentrations than potassium, but the slope was lower, and was associated with a rise in resistance. When potassium and calcium were applied together in ratios at which the calcium level was just sufficient to annul the K+-induced block of conjugation, the membrane was depolarized only slightly more than in potassium alone, and resting resistance was near the control level. It is therefore proposed that high [K+]o blocks co-stimulation by acting upon membrane resting conductance.
Regulation of Labellar and Tarsal Taste Thresholds in the Black Blowfly, Phormia Regina
Authors: Sudlow Leland C. , Edgecomb Robert S. , Murdock Larry L. 
Published: April 2021

ABSTRACT
Regulation of taste thresholds in the blowfly, Phormia regina Meigen, was investigated by manipulating the nutritional status of the insect and determining the effect on labellar and tarsal taste thresholds. Two feeding paradigms were employed: single meals administered to hungry flies, and ad libitum feeding of aqueous sucrose solutions for 4–5 days.
Flies which had fed on aqueous sucrose for several days exhibited high labellar and tarsal thresholds, with tarsal thresholds always higher than labellar thresholds. Food deprivation caused labellar and tarsal thresholds to decline. There was a positive logarithmic relationship between crop mass and labellar or tarsal thresholds. Consumption of single meals of aqueous sucrose caused increases in labellar thresholds similar to those for tarsal thresholds.
Labellar thresholds in flies fed ad libitum were not affected by transection of the recurrent nerve (RN) or the median abdominal nerve (MAN). Tarsal thresholds, in contrast, were markedly attenuated by RN transection but not by MAN transection. Transection of the RN in hungry flies prior to feeding them a single meal did not prevent the normal post-prandial rise in labellar thresholds. In earlier experiments, RN transection has been shown to attenuate the post-prandial rise in tarsal thresholds.
It appears that labellar and tarsal thresholds in the blowfly are similarly affected by consumption of aqueous sucrose. However, inhibitory feedback from the RN, which is partially responsible for elevation of tarsal thresholds after a meal, does not affect labellar thresholds. Additional, still unidentified, factor(s) may regulate both labellar and tarsal thresholds.
Correlation of Electrical and Mechanical Activity of Holothurian Muscle
Authors: Hill Robert B. 
Published: April 2021

ABSTRACT
Spontaneous contractions of segments of an isolated longitudinal muscle of Holothuria cinerascens are not propagated across a sucrose gap. Asynchronous spiking and spontaneous depolarizations leading to contraction can be recorded independently on each side of the gap. Caffeine-induced contractures are not the result of depolarization. Depolarization with KCl temporarily restores contractility lost in a series of caffeine-induced contractures. Acetylcholine causes a depolarization which induces contraction. Individual muscle units may spike quite independently as depolarization progresses in a spontaneous contraction.
The Influence of Hyperoxia, Hypoxia and Temperature on the Respiratory Physiology of the Intertidal Rockpool Fish Gobius Cobitis Pallas
Authors: Berschick P. , Bridges C. R. , Grieshaber M. K. 
Published: April 2021

ABSTRACT
The influence of hypoxia, hyperoxia and temperature on the oxygen consumption, heart rate and ventilation frequency of the intertidal rockpool fish Gobius cobitis Pallas were investigated to examine the respiratory adaptations of this species to intertidal conditions.
The standard mass-specific oxygen consumption during normoxia, calculated for a 50-g fish, averaged 1·27 mmol O2 kg−1 h−1 at 12·5°C and 3·62mmol O2kg−1 h−1 at 25°C. The Q10 value for oxygen consumption averaged 2·3.
During a stepwise reduction of oxygen partial pressure the oxygen consumption was maintained down to a critical oxygen tension, Pc, of approximately 43 Torr (1 Torr = 133·3 Pa). Ventilatory frequency increased progressively while heart rate remained constant until the was reduced below 16 Torr.
During hyperoxic exposure , oxygen consumption remained constant at 12·5 and at 25°C (Q10 = 2·3). Hyperoxia had no effect on heart rate, although ventilation frequency decreased with increasing (to the same extent at both temperatures), indicating the overriding effect of hyperoxia on ventilatory frequency.
Gobius cobitis appears to be well-adapted to the respiratory stresses which occur on a daily basis within intertidal rockpools.
Short Communication: Allometry of Lung Volume During Voluntary Submergence in the Saltwater Crocodile Crocodylus Porosus
Authors: Wright Jonathan C. , Kirshner David S. 
Published: April 2021

ABSTRACT
During submergence, the volume of gas stored in the lungs of a reptilian diver functions not only as an O2 store and CO2 sink (Lenfant, Johansen, Petersen & Schmidt-Nielsen, 1970; Burggren & Shelton, 1979; Seymour, 1982) but can also be adjusted to achieve the desired buoyant state. Lung volume during voluntary submergence will often be a compromise between these two basic functions and should also increase with body mass. The relationship between submergence lung volume and body mass will depend on how tissue density and specific gravity selected by a submerged animal vary with body mass. Previous studies have determined the relationship between lung volume and body mass in reptiles from maximally inflated lungs of dead specimens and have calculated an interspecific scaling factor of 0·75 (Tenney & Tenney, 1970; Wood & Lenfant, 1976). This suggested that the lung volume of a reptile may scale in accordance with mass-specific aerobic metabolism which also has a scaling factor close to 0·75 (Tenney & Tenney, 1970). Although equations generated from interspecific data from maximally inflated lungs are useful for describing certain morphological characteristics of reptilian lungs (Perry, 1983), they are probably inappropriate for determining the lung volume selected by a conscious, undisturbed reptile while voluntarily submerged.
Intestinal Salt Absorption in the Stenothermic Antarctic Fish, Notothenia Rossii
Authors: Gibson J. S. , Ellory J. C. 
Published: April 2021

ABSTRACT
All Antarctic fish studied so far show two adaptive strategies to life at sub-zero water temperatures; antifreeze glycoproteins, which act non-colligatively to inhibit ice propagation (DeVries, 1983), and elevated plasma electrolyte levels (150–200mosmolI−1 higher than that of temperate marine teleosts: Holmes & Donaldson, 1969; Dobbs & DeVries, 1975; O’Grady, Ellory & DeVries, 1983), equivalent to a freezing point reduction of 0·4°C. However, Prosser, Mackay & Kato (1970) have argued that the elevated plasma Na+ concentration is an energy-saving device, resulting in a smaller concentration gradient between fish plasma and salt water, which allows the composition of the former to be maintained at a lower metabolic cost.
Arterial Haemodynamics in the Cephalopod Mollusc, Octopus Dofleini
Authors: Shadwick Robert E. , Gosline John M. , Milsom William K. 
Published: April 2021

ABSTRACT
Simultaneous measurements of blood pressure and blood flow were made in the dorsal aorta of the cephalopod Octopus dofleini Wülker. In resting animals the heart rate varied from 8 ·5 to 14 beatsmin−1, while aortic pressure typically ranged from about 2·5 kPa at end diastole to 5 ·5 kPa at peak systole. Blood flow rate varied with pressure, averaging 0· 9mls−1, with peak flow rates of l·4–2·8mls−1. A slow asymptotic decline in both pressure and flow during the 2- to 4-s diastolic period indicated that the aorta functions as an elastic reservoir, as previously predicted. Aortic impedance spectra were derived from digitized pressure and flow data. The impedance amplitude decreased continuously with increasing frequency, while the impedance phase was always negative. These results are consistent with a two-element Windkessel model of the arterial system. The apparent pressure wave velocity, determined from transit times of pressure pulses in vivo, was &gt;10ms−1. This was much higher than the intrinsic wave velocity we predicted from in vitro measurements of aortic elasticity. This anomaly occurred because the length of the aorta represented less than 1 % of the wavelength of the fundamental pulse frequency, due to the low heart rate in this species. Consequently, arterial haemodynamics in O. dofleini are dominated by strong wave reflections, but do not exhibit other wave propagation effects which are typical of mammalian circulatory systems. Thus, the simple Windkessel model adequately describes the arterial circulation of this species of cephalopod.
Oxygen Consumption of the Isolated Heart of Octopus: Effects of Power Output and Hypoxia
Authors: Houlihan D. F. , Agnisola C. , Hamilton N. M. , Genoino I. Trara 
Published: April 2021

ABSTRACT
A technique is described which allowed the measurement of the oxygen consumption of the isolated heart of Octopus vulgaris. Contraction of the heart resulted in an aortic output and a flow through the heart muscle into coronary veins (the coronary output). The flow and oxygen content of the aortic output and the coronary output were measured with variable input pressures and constant output back pressure (volume loaded), variable output back pressure and constant aortic output (pressure loaded), and during hypoxia. Volume loading of the heart resulted in an increase in aortic output, power output and total oxygen consumption. Pressure loading increased power output and total oxygen consumption of the heart. Exposure to hypoxia decreased the aortic output, power output and total cardiac oxygen consumption. In the response of the heart to reduced work, brought about either by a reduced input pressure or by hypoxic perfusate, the power output was linearly related to the total oxygen consumption of the heart.
The oxygen extracted from the coronary output accounted for 80–100% of the total oxygen consumption of the heart. Coronary output amounted to 30% of the total cardiac output at maximum power output. In volume-loaded hearts the volume of the coronary output increased as aortic output increased ; in pressure-loaded hearts coronary output increased as power output increased, but aortic output remained constant. In hypoxia, the coronary output increased as the aortic output fell. At a perfusate of around 50Torr (1 Torr = 133 Pa), the aortic output ceased although the heart continued to beat and the coronary output continued, accounting for all of the oxygen consumption of the heart. The coronary output flow in vitro therefore has the capacity to be varied independently of the aortic output flow to maintain the oxygen supply to the perfused cardiac muscle.
Ionic Permeabilities of the Isolated Gill Cuticle of the Shore Crab Carcinus Maenas
Authors: Lignon J. M. 
Published: April 2021

ABSTRACT
Electrical parameters of the cuticle of the posterior gill lamella of the shore crab Carcinus maenas, were measured. When the cuticle was perfused with crab saline (CS) inside and sea water (SW) outside, ionic replacements or dilutions of the bathing solutions produced changes in potential that showed a selective permeability to cations with respect to anions. Similar measurements made with the cuticle bathed in single salt solutions gave the following permeability sequence: NH4+ &gt; Rb+ &gt; Cs+ &gt; K+ &gt; Na+ ≈ Ca2+ &gt; Li+ &gt; Tns+ &gt; Mg2+ &gt; HCO3−&gt; CH3COC− &gt; cl−&gt;so42−.
From conductance measurements, the permeability of the cuticle to Ca2+ and Na+ was about 10−3cms−1. K+ and NH4+ were about five times more permeant, while Mg2+ permeability was 5 × 10−5 cm s−1. The permeability of the cuticle to anions 1 ay between 10−6 and 10−5cms−1. In addition, the cuticle showed an asymmetrical behaviour. These results suggest that the low anionic cuticular permeability can interfere with ionic exchanges across the whole gill.
Blood Flow and Pressure Changes in Exercising Octopuses (Octopus Vulgaris)
Authors: Wells M. J. , Duthie G. G. , Houlihan D. F. , Smith P. J. S. , Wells J. 
Published: April 2021

ABSTRACT
Pressure and flow were recorded from the dorsal aorta of freely moving Octopus vulgaris at rest and in exercise. Mean blood pressure, the amplitude of pressure pulses and flow all double as the animal moves about. Frequency changes little in exercise, indeed the increased pulses may be associated with a small drop in heartbeat frequency. There is little or no scope for expansion of arteriovenous oxygen content difference. So the increase in cardiac output necessitated by exercise must be achieved almost solely by an increase in the stroke volume of the systemic heart.
Jet propulsion is accompanied by cardiac arrest. Measurements of internal mantle pressures during jetting and of the pressure pulses generated by peristalsis of the great veins suggest that the venous system is incapable of returning blood against the gradients produced by the rise in mean mantle pressure. Since the oxygen debt that can be sustained by Octopus is quite small (≈22mlO2kg−1), jet-propelled movement is impossible for distances of more than a few metres.
Problems of the maintenance of a circulation in an animal with a high metabolic rate and the basic body plan of a mollusc are discussed, and the situation in squid is compared with that in octopuses.
The Contractile Properties of a Crab Respiratory Muscle
Authors: Josephson Robert K. , Stokes Darrell R. 
Published: April 2021

ABSTRACT
Contraction of scaphognathite muscle L2B of the green crab Carcinus maenas is strongly dependent on stimulus number and frequency. Single, supramaximal stimuli evoke little or no tension. When stimulated with shocks in either short bursts (10 stimuli in 0·5 s or less) or long bursts (5 s of stimulation), the isometric tension from the muscle increases with increasing stimulus frequency to a maximum at about 150 Hz at 15°C, beyond which tension declines with further increase in stimulus frequency. There can be facilitation of both contraction and relaxation between short bursts of stimuli. Facilitation of contraction is seen as increasing tension on successive bursts of a series, even when the interburst interval is long enough for relaxation to be completed during the interval. Interburst facilitation lasts at least 10 s. Facilitation of relaxation is seen as progressively faster relaxation from burst to burst of a series, and relaxation to lower tension levels when the interburst interval is so short that relaxation is incomplete in the interburst interval. Maximum isometric tension occurs at muscle lengths slightly longer than the longest muscle length reached in vivo. Tension declines rapidly with changes in muscle length away from the optimum length. The maximum isometric tension was about 12 N cm−2. The maximum shortening velocity of a tetanically activated muscle was determined as 1·9 lengths s−1 (Ls−1) by extrapolation of force-velocity curves to zero force and 3·3 Ls−1 by slack test measurements. The scaphognathite muscle would be classified as a slow or tonic muscle on the basis of its requirements for multiple stimulation to reach full activation, and as a moderately fast muscle on the basis of its force-velocity properties.
Salt and Water Regulation in Macrobdella Decora (Hirudinea: Gnathobdelliformes) Under Osmotic Stress*
Authors: Wenning Angela 
Published: April 2021

ABSTRACT
The anatomy, ultrastructure and innervation of the nephridia of the North American leech, Macrobdella decora (Say), are described. The osmotic concentrations of blood, crop fluid and final urine, as well as urine flow under normal conditions, were found to be similar to those of the well-studied European medicinal leech, Hirudo medicinalis L.
The capacity of the excretory system after changes in external salinity, and after salt and water loading with artificial blood meals, was investigated. In contrast to H. medicinalis, M. decora does not tolerate hypertonic environments and is less efficient in rapidly excreting excess salt and water. Three factors make salt and water regulation in M. decora different from that in H. medicinalis; a slower fluid resorption from the crop, a limited transport capacity of the primary urine-forming cells, and a lower rate of salt reabsorption in the central canal.
Saxitoxin differentiates between two types of Na+-dependent potentials in the retzius cell of hirudinid leeches
Authors: Johansen J. , Kleinhaus A. L. 
Published: April 2021

ABSTRACT
The effects of tetrodotoxin (TTX) and saxitoxin (STX) on the action potentials recorded in Ca2+-free solution in the absence of Ca2+ and K+ currents were investigated in the Retzius cell of three hirudinid leech species (Hirudo medicinalis, Macrobdella decora and Poecilobdella granulosa) and in the glossiphoniid leech Haementeria ghilianii.
In the four leech species, stimulation of the Retzius cell in the presence of 25 mmol l-1 tetraethylammonium chloride (TEA), 3 mmol l−1 4-aminopyridine (4-AP) and 2 mmol l−1 Mn2+ evoked prolonged action potentials consisting of an initial fast-rising spike followed by a plateau lasting several hundreds of milliseconds. The amplitude and duration of both components of action potentials recorded under these conditions were dependent on [Na+]o.
In the hirudinid leeches the initial spike was unaffected by TTX and STX whereas the plateau was selectively blocked by micromolar concentration of STX. In Haementeria both the initial spike and the subsequent plateau were sensitive to nanomolar concentrations of STX and TTX with an estimated ED50 of approximately 20 nmol l−1 for inhibition of of the fast spike.
The results suggest that there are two types of ionic currents mediating the two distinct components of Na+-dependent action potentials in the Retzius cell: (1) a fast-inactivating one, presumably underlying the normal spike which is TTX-and STX-resistant in hirudinid leeches but sensitive to both agents in Haementeria and (2) a low-threshold, prolonged current which underlies the plateau recorded from these cells in the absence of Caz+ and K+ currents and which is selectively blocked by STX in hirudinid leeches but sensitive to both STX and TTX in Haementeria.
It is likely that the variable kinetic and pharmacological properties that characterize the various Na+ potentials in these identified homologous neurones may be of functional significance and result from differences in the molecular structure of their Na+ channels.
Gas Exchange in the Loggerhead Sea Turtle Caretta Caretta
Authors: Lutcavage M. E. , Lutz P. L. , Baier H. 
Published: April 2021

ABSTRACT
Pulmonary CO diffusion capacity (DLCO), lung volume (VL), oxygen uptake and pulmonary blood flow (Q̇L) were measured simultaneously in the loggerhead sea turtle Caretta caretta (Linnaeus) (8-11 kg) using a gas rebreathing technique (syringe pump ventilation).
Calculated DLCO and values in the loggerhead turtle are approximately twice those of non-varanid reptiles and about 25 % of values for resting mammals. Evidence based on an estimated lung-capillary O2 gradient, , shows that only a small driving gradient is required for O2 conductance across the loggerhead turtle lung. Pulmonary blood flow values are high compared to those for other reptiles; on the basis of the Fick principle, this implies a substantial blood convection requirement.
Differences in oxygen transport mechanisms between the loggerhead sea turtle and other highly aerobic but terrestrial reptiles may result from divergent lung structures and breathing patterns. In sea turtles, the coupling of respiration with locomotory behaviour is one factor that may limit aerobic performance. Since sea turtles have only intermittent access to air, they are required to load both arterial and venous blood with O2 before submerging.
Localization of FMRFamide-like peptides in the snail Helix aspersa
Authors: Lehman H. K. , Price D. A. 
Published: April 2021

ABSTRACT
The distribution of FMRFamide-like material in the gastropod mollusc, Helix aspersa, was studied by radioimmunoassay (RIA) and immunocytochemistry. Most of the RIA activity was concentrated in the central nervous system, the male reproductive tract, the tentacles and the posterior digestive system (Table 1). The density of FMRFamidergic perikarya, nerves and nerve varicosities in the muscle tissue of all these regions, as indicated immunocytochemically (Fig. 2), was well correlated with the distribution as determined by RIA.
Gel chromatography of each extract resolved two peaks of FMRFamide-like immunoreactivity (Fig. 3). The first of these was further analysed by high-pressure liquid chromatography (HPLC), and the components included two major immunoreactive peaks identifiable, both by their retention times and their effects on the radula protractor muscle of Busycon contrarium, as the known peptides FMRFamide and pQDPFLRFamide (Figs 4–6). The second peak from gel chromatography gave only a single peak, distinct from that of FMRFamide and pQDPFLRFamide, in two HPLC systems (Fig. 7), but it did not behave like a competitive ligand in the FMRFamide RIA. Moreover, its immunoreactivity, unlike any peptides we tested, was not affected by carboxypeptidase Y (Fig. 8), and it was not active on the radula protractor muscle. Thus, it is certainly not an FMRFamide-like peptide.
We conclude that Helix aspersa contains at least two FMRFamide-like peptides, FMRFamide and pQDPFLRFamide. These peptides appear to act both as neurohormones and as neurotransmitters or modulators in the central ganglia, reproductive, digestive, muscular and circulatory systems.
Habituation of the cardiac response to involuntary diving in diving and dabbling ducks
Authors: Gabbott G. R. , Jones D. R. 
Published: April 2021

ABSTRACT
Bradycardia in response to forced submergence was habituated in dabbling (Anas platyrhynchos, Linnaeus) and diving (Aythya americana, Eyton) ducks by repetitively submerging the animals, each day for several days, for periods of 40 and 20 s, respectively. The onset of pronounced bradycardia was delayed with each successive trial, until little or no bradycardia occurred during submergence. Diving bradycardia is driven by chemoreceptors in the dabbler and caused by stimulation of narial receptors in the diver. Mean arterial blood pressure in dives was unchanged from pre-dive levels in both naive and trained dabbling ducks. and pHa at the end of a dive were similar before and after habituation training. Bradycardia occurred in dives by habituated dabbling ducks if the animal breathed 15 % O2 before submergence. The ventilator responses to breathing high and low levels of oxygen were unaffected by habituation training. The changes in blood gases during dives by naive and habituated dabbling ducks were the same: therefore, in the absence of a demonstrated decrement in receptor chemosensitivity or efferent potency, the locus of habituation must reside in the central nervous system.