bluuebunny/crossref_metadata_2025 huggingface dataset:
Feeding Performance And Muscular Constraints In Fish
Authors: Aerts Peter , Vree Frits De
Published: April 2021

Analysis of the feeding kinematics of Astatotilapia (a small cichlid fish) suggests the presence of peripheral feedback modulation of the motor pattern, allowing the act of suction to be abbreviated. In this way, the effort spent in suction is minimized. The biological significance of the development of such a modulating feedback system is not immediately obvious from a ‘classical ecological’ point of view. It is postulated that the muscular metabolism itself might constrain the short, transient and strenuous motor output typical of suction feeding. Thus, reducing the suction effort makes sense when successive strenuous head-part movements are immediately required for additional suction, buccal transport or spitting. This hypothesis was tested by in vivo electrical stimulation of muscles important in feeding: the epaxials, which lift the skull and expand the buccal cavity. Reliable stimulation variables for the epaxial muscles were determined from preliminary stimulation experiments and from electromyographic recordings of these muscles in a specimen feeding on crickets. Stimulation trains of variable duration (<150ms) were applied in series of five trains. The intervals between trains were variable as well (<1s). The mechanical output was measured by means of an accelerometer, a force transducer or a magnetoresistive displacement transducer. In the latter case, the time course of the mechanical output could be recorded and analysed. The hypothesis predicts a decrease in the muscular output with increasing effort (long trains) and fast repetition (short intervals). The experimental results show the expected decline in mechanical output from one stimulation train to the next when longer stimulation bursts are imposed in quick succession. Statistical analyses (multiple regression) showed that train length, train rate and train number contribute significantly to the observed variation in mechanical output, supporting the hypothesis. Explanations for the phenomena are discussed.
The Energetic Costs of Calling in the Bushcricket Requena Verticalis (Orthoptera: Tettigoniidae: Listroscelidinae)
Authors: Bailey W. J. , Withers P. C. , Endersby M. , Gaull K.
Published: April 2021

The metabolic costs of calling for male Requena verticalis Walker (Tettigoniidae: Listroscelidinae) were measured by direct recordings of oxygen consumption. The acoustic power output was measured by sound pressure levels around the calling bushcricket. The average metabolic cost of calling was 0.143ml g−1 h-1 but depended on calling rate. The net metabolic cost of calling per unit call, the syllable, was calculated to be 4.34×10−6±8.3X10−7 ml O2 syllable−1 g−1 bodymass (S.E.) from the slope of the relationship between total and rate of syllable production. The resting , calculated as the intercept of the relationship, was 0.248ml O2 g−1 bodymass h−1. The energetic cost of calling for R. verticalis (average mass 0.37g) was estimated at 31.85×10−6 J syllable−1. Sound pressure levels were measured around calling insects. The surface area of a sphere of uniform sound pressure level [83dB SPL root mean square (RMS) acoustic power] obtained by these measurements was used to calculate acoustic power. This was 0.20mW. The metabolic efficiency of calling, based on total metabolic energy utilisation, was 6.4%. However, we propose that the mechanical efficiency for acoustic transmission is closer to 57%, since only about 10% of muscle metabolic energy is apparently available for sound production. R. verticalis emits chirps formed of several syllables within which are discrete sound pulses. Wing stroke rates, when the insect is calling at its maximal rate, were approximately 583min−1. This is slow compared to the rates observed in conehead tettigoniids, the only other group of bushcrickets where metabolic costs have been measured. The thoracic temperatures of males that had been calling for 5min were not significantly different from those of non-calling males. For R. verticalis, calling with relatively slow syllable rates may reduce the total cost of calling, and this may be a compensatory mechanism for their other high energetic cost of mating (a large spermatophylax).
Active Na+-, Cl−-and Hco3−-Dependent Acid Extrusion in Atlantic Cod Red Blood Cells in Winter Activated by Hypercapnia
Authors: Berenbrink M. , Bridges C. R.
Published: April 2021

The relationship between intracellular pH (pHi) and extracellular pH (pHe) was investigated in red blood cells from the Atlantic cod (Gadus morhua) in carbon dioxide/bicarbonate-buffered salines. In summer animals (August/September), similar transmembrane distribution ratios of chloride ([Cl−]i/[Cl−]e=rCl−) and protons ([H+]e/[H+]i=rH+) suggested a passive Donnan distribution of these ions across the red blood cell membrane at pHe 6.7–8.4. In winter animals (February/March), a marked discrepancy occurred between rH+ and rCl− at low pHe values. The pronounced increase in rH+ resulted in significantly higher pHi values compared with those of red blood cells from summer animals and at pHe 6.7 pHi exceeded pHe by 0.3 units. The increases in rH+ values were completely abolished by cyanide and 2,4-dinitrophenol. The high disequilibrium rH+ values were sodium-, chloride-and bicarbonate-dependent. During hypercapnic acidosis, proton equivalents were extruded from the red blood cell. The resulting high rH+ values were accompanied by a reduced chloride shift into the red blood cell and a ouabain-insensitive net sodium influx. The net sodium influx into red blood cells from winter animals was significantly reduced in the presence of DIDS (4,4′-diisothiocyanatostilbene-2,2′-disulphonic acid). The results suggest the activation of a Na+-dependent Cl−/HCO3−exchanger at low pHe in the red blood cells of the Atlantic cod in winter.
Glycolytic Function in Goldfish Hepatocytes at Different Temperatures: Relevance for Na+ Pump Activity and Protein Synthesis
Authors: Krumschnabel Gerhard , Malle Sabine , Schwarzbaum Pablo J. , Wieser Wolfgang
Published: April 2021

Cellular metabolism of ectotherms may respond to temperature changes with a shift in the choice of substrate preferentially catabolized for ATP production (Johnston and Dunn, 1987). This has been shown in acclimated fish, in which a temperature-dependent switch from carbohydrates as the main fuel for energy metabolism to other fuels, or vice versa, can occur. Such shifts help to indicate the relative importance of aerobic glycolysis as an ATP-supplying process. The preferred energy source at a given temperature depends upon the temperature range investigated, as well as on the species, on the tissue and upon nutritional factors. The adaptive significance of shifts between energy sources is not always clear. While in some cases ecological arguments may provide plausible explanations (e.g. seasonal adaptation to migration and reproductive requirements; Stone and Sidell, 1981; Moerland and Sidell, 1981), evidence is accumulating that structural or functional features inherent in the metabolic organisation of the cell may also play a role in determining the nature of such responses (Sidell, 1983; Sidell and Hazel, 1987). Of particular relevance in this respect is the interaction between diffusional flux and the rate of enzymatic activity in shaping specific temperature effects on cellular metabolism.
On The Respiratory Flow in the Cuttlefish Sepia Officinalis
Authors: Bone Q. , Brown E. R. , Travers G.
Published: April 2021

The respiratory flow of water over the gills of the cuttlefish Sepia officinalis at rest is produced by the alternate activity of the radial muscles of the mantle and the musculature of the collar flaps; mantle circular muscle fibres are not involved. Inspiration takes place as the radial fibres contract, thinning the mantle and expanding the mantle cavity. The rise in mantle cavity pressure (up to 0.15 kPa), expelling water via the siphon during expiration, is brought about by inward movement of the collar flaps and (probably) mainly by elastic recoil of the mantle connective tissue network ‘wound up’ by radial fibre contraction during inspiration. Sepia also shows a second respiratory pattern, in which mantle cavity pressures during expiration are greater (up to 0.25 kPa). Here, the mantle circular fibres are involved, as they are during the large pressure transients (up to 10 kPa) seen during escape jetting. Active contraction of the muscles of the collar flaps is seen in all three patterns of expulsion of water from the mantle cavity, electrical activity increasing with increasing mantle cavity pressures. Respiratory expiration in the resting squid Loligo vulgaris is probably driven as in Sepia, whereas in the resting octopus Eledone cirrhosa, the mantle circular musculature is active during expiration. The significance of these observations is discussed.
Swimming Metabolism of Wild-Type and Cloned Zebrafish Brachydanio Rerio
Authors: Plaut Itai , Gordon Malcolm S.
Published: April 2021

The availability of a gynogenetic isogenic homozygous diploid clonal strain (C) of the zebrafish (Brachydanio rerio), combined with the small adult body size of the species, made possible a study of the following two questions. (1) Is the genetic uniformity of a group of fish reflected in decreased variability of features of organismic performance physiology? (2) Is the metabolic cost of subcarangiform swimming significantly different in small fishes compared with large ones?

Wild-type (WT) and C strain zebrafish maintained at 28°C can all swim very rapidly [up to relative swimming speeds of 13 body lengths s −1 (BL s −1)] for extended periods (at least 2 h) without visibly tiring. Oxygen consumption rates were measured for both types at swimming speeds of 1.5–13 BL s −1. Whole-body lactate concentrations were also measured during routine activity and after prolonged exercise for both fish types. The slopes of the linear regressions between the logarithm of mass-specific oxygen consumption rates and relative swimming speeds for WT zebrafish were low (0.010–0.024) and were not significantly different from zero. Regression slopes were also low (0.009–0.026), but different from zero, for C zebrafish. Standard metabolic rates were 0.60–1.54 and 0.40–0.85 ml O2 g−1 h−1 for WT and C zebrafish respectively. Variances of slopes were significantly larger for WT than for C fish. Whole-body lactate concentrations and their variances were not significantly different between types and between rested and exercised fishes. The results demonstrate unusual swimming performance capacities, a remarkably low cost of swimming and some reductions in variability of C fish. Several possible explanations for the results are discussed.
Capillary Blood Transit Time in Muscles in Relation to Body Size and Aerobic Capacity
Authors: Kayar S. R. , Hoppeler H. , Jones J. H. , Longworth K. , Armstrong R. B. , Laughlin M. H. , Lindstedt S. L. , Bicudo J. E. P. W. , Groebe K. , Taylor C. R. , Weibel E. R.
Published: April 2021

The mean minimal transit time for blood in muscle capillaries (tc) was estimated in six species, spanning two orders of magnitude in body mass and aerobic capacity: horse, steer, dog, goat, fox and agouti. Arterial and mixed venous blood O2 concentrations, blood hemoglobin concentrations ([Hb]) and oxygen uptake rates were measured while the animals ran on a treadmill at a speed that elicited the maximal oxygen consumption rate from each animal. Blood flow to the muscles (Q̇m) was assumed to be 85% of cardiac output, which was calculated using the Fick relationship. Total muscle capillary blood volume (Vc) and total muscle mitochondrial volume were estimated by morphometry, using a whole-body muscle sampling scheme. The tc was computed as Vc/Q̇m. The tc was 0.3–0.5 s in the 4 kg foxes and agoutis, 0.7–0.8 s in the 25 kg dogs and goats, and 0.8–1.0 s in the 400 kg horses and steers. The tc was positively correlated with body mass and negatively correlated with transcapillary O2 release rate per unit capillary length. Mitochondrial content was positively correlated with and with the product of Q̇m and [Hb]. These data suggested that Q̇m, Vc, maximal hemoglobin flux, and consequently tc, are co-adjusted to result in muscle O2 supply conditions that are matched to the O2 demands of the muscles at
Mechanisms of K+ Uptake Across the Basal Membrane of Malpighian Tubules of Formica Polyctena: The Effect of Ions and Inhibitors
Authors: Leyssens A. , Dijkstra S. , Van Kerkhove E. , Steels P.
Published: April 2021

In the presence of 6 mmol l−1 Ba2+, known to block the K+ channels in the basal membrane, a rise in bath [K+] ([K+]bl) induced an increase in intracellular K+ concentration ([K+]i) similar in amount and in time course to that obtained in the absence of Ba2+. The presence of active and passive (other than through K+ channels) K+ uptake mechanisms across the basal membrane was investigated in different bath K+ concentrations. Dihydro-ouabain (10−3 mol l−1), a blocker of the Na+/K+-ATPase, tested in low bath [K+], and Sch28080 (10−4 mol l−1), a K+/H+-ATPase inhibitor, were without effect on fluid secretion. Dihydro-ouabain was also without effect on electrical potential differences either in the absence or in the presence of Ba2+. Vanadate (10−3 mol l−1), in contrast, strongly reduced fluid secretion not only in control solution but also in high-K+, Na+-free medium and reduced the transepithelial and the apical membrane potential differences but not the basal membrane potential difference or [K+]i. Omitting Na+ from the bathing medium, replacing Cl-by Br− or applying bumetanide (10−5 mol l−1) inhibited fluid secretion only in a low-K+ (10 mmol l−1) medium. In 51 mmol l−1 [K+]bl, omitting Na+ was without effect and 10-4 mol l−1 bumetanide was needed to inhibit secretion. Replacing Cl−by Br−stimulated fluid secretion at this K+ concentration. Bumetanide (10−4 mol l−1) had no effect in 113 mmol l−1 [K+]bl. Bumetanide (10−4 mol l−1) in 51 mmol l−1 [K+]bl did not affect membrane potentials, did not lower [K+]i and did not affect the rise in [K+]i observed on an increase in [K+]bl. The results were summarized in a model proposing that K+ channels play a dominant role in high-K+ (113 mmol l−1) bathing medium. A K+/Cl−cotransporter may become more important in 51 mmol l−1 [K+]bl and a K+/Na+/2Cl− cotransporter may gain in importance in 10 mmol l−1 [K+]bl. Active mechanisms for K+ uptake across the basal membrane seem to play no detectable role in sustaining fluid secretion. The response to vanadate might be due to an effect on the apical electrogenic H+ pump.
The Shift in Visual Pigment Dominance in the Retinae of Juvenile Coho Salmon (Oncorhynchus Kisutch): an Indicator of Smolt Status
Authors: Alexander G. , Sweeting R. , McKeown B.
Published: April 2021

Smolting juvenile coho salmon were sampled to determine (1) whether a correlation between hypo-osmoregulatory ability and visual pigment composition existed and (2) whether the hormone 3,5,3′-tri-iodothyronine (T3) was playing a role in the visual pigment conversion process. Plasma sodium levels of seawater-challenged fish (30 ‰) indicated that there was a 5 week period of optimal ability to excrete excess plasma sodium ions (hypo-osmoregulation) in the late spring/early summer that represented the ‘window of opportunity’ for the entry or introduction to sea water of the salmon. Early in the smoltification process, the vitamin-A2-based visual pigment porphyropsin increased its dominance in the retinae, and radioimmunoassay of plasma indicated that T3 levels were at a maximum prior to this increase in porphyropsin. As the parr–smolt transformation continued, there was a steady decrease in the relative amounts of porphyropsin, indicating that the retinae were favouring the acquisition of rhodopsin. Rhodopsin dominance virtually coincided with the period of best hypo-osmoregulatory ability. Subsequently, the salmon showed a loss of hypo-osmoregulatory ability and concomitant increases in the amount of porphyropsin in the retina were observed. The relationship between the visual pigment shift and the smoltification process is discussed in terms of preparation for migration and thyroid hormone involvement, and the use of retinal visual pigment composition as an index of smolt status is proposed.
Extraocular Sensitivity to Polarized Light in an Echinoderm
Authors: Johnsen Sönke
Published: April 2021

This study tests the hypotheses that the birefringent calcite and stereom structure of the brittlestar (Ophiuroidea, Echinodermata) endoskeleton polarizes light and that certain brittlestars respond to polarized light. The first hypothesis was tested in Ophioderma brevispinum by examining ossicles from freshly killed specimens under polarized light. This analysis revealed that the lateral arm shields, oral arm shields, arm spines and aboral disk ossicles are dichroic and thus polarize light. The second hypothesis was tested in two orientation experiments under polarized light. The results from the first orientation experiment showed (1) that, under polarized light, animals oriented significantly and unimodally, (2) that, under polarized light with the e-vector perpendicular to that in 1, animals oriented significantly and unimodally to within 18° of the bearing of the animals in 1, and (3) that, under unpolarized light, animals did not orient significantly. The results from the second orientation experiment showed that, under polarized light, animals oriented significantly and unimodally to within 17° of an individual preference previously established under polarized light; but under unpolarized light, animals did not orient significantly to an individual preference established under polarized light. Thus, O. brevispinum orients under polarized, but not unpolarized, light. The unimodal orientation and lack of consistent alignment with the e-vector suggest that polarized light is not used as a directional cue but instead as a signal to sustain oriented behavior. The dichroism of the ossicles of O. brevispinum and the animal’s capacity (though eyeless) to discriminate between polarized and unpolarized light suggest that the mechanism of polarization sensitivity may rely on polarizing filters built from the animal’s skeleton.
Special Transport and Neurological Significance of two Amino Acids in a Configuration Conventionally Designated as D
Authors: Christensen Halvor N. , Greene Alice A. , Kakuda Donald K. , MacLeod Carol L.
Published: April 2021

We point out an ability of certain amino acids to be recognized at a biological receptor site as though their amino group bore, instead of an α. relationship to a carboxylate group, a β, γ or δ relationship to the same or a second carboxylate group. For aspartate, the unbalanced position of its amino group between a pair of carboxylates allows its occasional biorecognition as a β - rather than as an α.-amino acid, whereas for proline and its homologs, their cyclic arrangement may allow the imino group, without its being replicated, to be sensed analogously as falling at either of two distances from the single carboxylate group. The greater separation might allow proline to be seen as biologically analogous to γ -aminobutyric acid. This more remote positioning of the imino group would allow the D-form of both amino acids to present its amino group in the orientation characteristic of the natural L-form. The dual modes of recognition should accordingly be signalled by what appears to be low stereospecificity, actually due to a distinction in the enantiorecognition of the two isomers. Competing recognition for transport between their respective D-and L-forms, although it does not prove that phenomenon, has been shown for proline and, significantly, even more strongly for its lower homolog, 2-azetidine carboxylate. Such indications have so far revealed themselves rather inconspicuously for the central nervous system binding of proline, reviewed here as a possible feature of a role suspected for proline in neurotransmission.
The Effect of Temperature on Spontaneous Action Potential Discharge of the Isolated Sinus Venosus From Winter and Summer Plaice (Pleuronectes Platessa)
Authors: Harper A. A. , Newton I. P. , Watt P. W.
Published: April 2021

The spontaneous cardiac pacemaker activity and conformation were recorded in vitro, using intracellular recording methods, from heart tissue of summer- and winter-caught plaice. The effects of changing temperature on the pacemaker rate, duration of action potential and diastolic depolarization were investigated by altering the temperature of the superfusing medium. The resting intrinsic rate of discharge was significantly greater in pacemaker cells from winter plaice (P=0.05), but there was no significant difference between winter and summer fish in the apparent Arrhenius activation energies for this process. However, there was a significant difference in the estimated intercept, indicating a thermal shift in the processes underlying the spontaneous pacemaker rhythm. There was no significant difference in the diastolic depolarization duration recorded from winter and summer fish over the temperature range 4–L22 °C. The major effect of previous environmental temperature was on the duration of the action potential (P<0.02), indicating that the observed changes in pacemaker discharge rate were not influenced by the processes that determine the duration of the pacemaker diastolic depolarisation but were modulated by the channel events that give rise to the action potential.
Coulometric Measurement Of Oxygen Consumption During Development Of Marine Invertebrate Embryos And Larvae
Authors: Hoegh-Guldberg Ove , Manahan Donal T.
Published: April 2021

Determining the metabolic rate of larval invertebrates from aquatic habitats is complicated by the problems of small size and the scarcity of suitable measurement techniques. In this study, coulometric respirometry (a new technique for the study of marine embryos and larvae) was used to explore several issues associated with the rate of energy use during embryonic and larval development of marine invertebrates from three phyla. Coulometric respirometry measures rates of oxygen consumption under normoxic conditions by electrochemically replacing the oxygen consumed by organisms during an experiment. This technique is based on the assumption that all electrons consumed by the anodic reactions result in the production of oxygen. We verify this assumption using direct measurements of oxygen production and show that the technique is sensitive enough (1 nmol O2 h-1) to quantify the oxygen consumption of a single individual swimming freely in a relatively large volume (2 ml). Continuous measurements can span days, and embryos in the coulometric respiration chambers develop to the larval stage at normal rates of differentiation. Measurements of metabolic rates were made with the coulometric respirometer during the complete life-span of larvae of three species (asteroid, Asterina miniata; bivalve, Crassostrea gigas; echinoid, Dendraster excentricus). For these species, metabolic power equations had mass exponents near unity (0.9–1.1), showing that metabolic rate scales isometrically with mass during larval growth. Metabolic rates were independent of the concentration of larvae used in the respirometer chambers for a range of larval concentrations from 4 to 400 larvae ml-1 (coulometric respirometer) and from 241 to 809 larvae ml-1 (polarographic oxygen sensor). Metabolic rates were measured using coulometric respirometry and two other commonly used techniques, polarographic oxygen sensors and Winkler’s titration. Polarographic oxygen sensors in small, sealed chambers (100 μl) consistently gave the lowest values (by as much as 80 %) for the asteroid, echinoid and molluscan larvae. By comparison, rates of oxygen consumption measured using coulometric respirometry and Winkler’s titration (to measure the change in oxygen concentration over time) were similar and consistently higher. Although the polarographic oxygen sensor is the most widely used method for measuring the metabolism of small animals in sealed 100–1000 μl chambers, it appears that the metabolism of some larvae is adversely affected by the conditions within these respirometers.
Plasticity of Muscle Contractile Properties Following Temperature Acclimation in the Marine Fish Myoxocephalus Scorpius
Authors: Beddow Toni A. , Johnston Ian A.
Published: April 2021

Live fibre bundles were isolated from the fast myotomal muscle of short-horned sculpin (Myoxocephalus scorpius L.) and isometric contractile properties and the force-velocity (P-V) relationship determined at 5, 10 and 15 °C. Experiments were carried out on winter-and summer-caught sculpins and on individuals acclimated for 6–8 weeks to either 5 or 15 °C (12h:12h light:dark). Maximum tetanic tension (P0) in fibres from 15 °C-acclimated fish increased from 125 kN m−2 at 5 °C to 282 KN−2 at 15 °C (R10=2.3). For 5 °C-acclimated fish, Po was 139 kN m−2 at 5 °C, but fell to 78 kN m−2 at 15 °C, consistent with a partial failure of excitation-contraction coupling at high temperatures. Peak force at 15 °C was increased 2.2 times following depolarisation with a high-K+ solution, but was unaffected by the addition of caffeine and/or eserine to the Ringer’s solution. The results from winter-and summer-caught fish were similar to those from 5 °C-and 15 °C-acclimated sculpins respectively. In 15 °C-acclimated fish, the power output of muscle fibres calculated from the P-V relationship was 55W kg−1 at 5 °C and 206 W kg21 at 15 °C. The P-V relationship at 5 °C was significantly less curved in muscle fibres from 5 °C-than from 15 °C-acclimated fish. After normalizing the curves for P0 and Vmax, it was found that the change in curvature was sufficient to produce a 40 % increase in relative power output at 5 °C in cold-acclimated fish. The maximum contraction speed of muscle fibres at 15 °C was 2.4 times higher in 15 °C-than in 5 °C-acclimated fish. It was concluded that acclimation modifies the contractile properties of fast muscle fibres at both low and high temperatures.
An Electrical Model For Periplaneta Americana Pronotal Integument: An Epidermal Location For Hydration-Dependent Resistance
Authors: Smith J. J. B. , Machin J. , Lampert G. J.
Published: April 2021

Measurements of electrical resistance appear to be useful indicators of porosity and related water permeability in insect cuticle. To develop an adequate understanding of how such measurements relate to the physical and structural properties of the integument, we made detailed determinations of resistance and impedance values for pronotal cuticle in adult male Periplaneta americana. The most consistent estimates were obtained by averaging measurements across the integument on both sides of the midline at several intervals starting 15 min after electrode application. Pronotal resistance varied inversely with water content, from about 10 kΩ cm2 in hydrated cockroaches to about 40 kΩ cm2 in dehydrated insects. Though the dermal gland canals appear to act as the main conductive pathway across the cuticle, the variable ‘barrier’ is located in the epidermal layer, since removal of the epidermis from isolated pronota also removes most of the variable component of the integumental resistance. Comparison of measurements between two external electrodes with single-electrode measurements revealed a ‘shunt’ pathway parallel to the cuticle surface; modelling this shunt suggested that it was variable and located mostly internal to the cuticle, supporting an epidermal location for a variable barrier. Impedance measurements over a range of frequencies showed the integument to be electrically complex, and a model is proposed to account for its properties
Why is There no Carbonic Anhydrase Activity Available to Fish Plasma?
Authors: Lessard Joanne , Val Adalberto L. , Aota Sumi , Randall David J.
Published: April 2021

Carbonic anhydrase (CA) is absent from the plasma of vertebrates. In vitro, CA in fish plasma will short-circuit the effect of catecholamines, which is to increase red blood cell (RBC) pH and volume, both of which enhance the affinity of hemoglobin for O2. CA was infused into trout for a period of 6h and injected after 48 h, during which the animal was submitted to deep hypoxia . O2 content, lactate content, catecholamine levels, hematocrit, hemoglobin concentration and pHi were similar to those in the saline-infused control group. In contrast, cell volume was significantly higher and pHe, total CO2 content and organic phosphate levels were significantly lower than in the control group. The concentration of CA was not high enough completely to short-circuit the increase in pHi and red blood cell volume caused by catecholamines. The lower pHe in the CA-infused animals could enhance the activity of the Na+/H+ pump, which would keep the nucleotide triphosphate levels low. pH is a balance between acid loading at the muscle and acid excretion at the gills or the kidneys; we cannot distinguish between which of these resulted in a decrease of plasma pH. In conclusion, CA in plasma did not cause the expected reduction in blood oxygen content but did have a marked effect on plasma total CO2 content.
The Structure and Physical Properties of Invertebrate and Primitive Vertebrate Arteries
Authors: Davison I. G. , Wright G. M. , Demont M. E.
Published: April 2021

Light and electron microscopy and in vitro inflation experiments were conducted on the aortae of three different invertebrate species: the lobster Homarus americanus, the horseshoe crab Limulus polyphemus and the whelk Busycon contrarium. Inflation experiments were also performed on the aortae of two species of primitive vertebrates, the sea lamprey Petromyzon marinus and the Atlantic hagfish Myxine glutinosa. The inflation experiments demonstrated similar overall biomechanical properties in each case, despite the existence of differences in tissue structure. The vessels were compliant at low strains, but demonstrated nonlinear elasticity, increasing in stiffness as strains increased; this property could act as protection against artery wall rupture. The vessels of the lamprey, hagfish and lobster are capable of acting as fairly efficient elastic reservoirs and of smoothing blood flow during circulation as they had low hysteresis values (13–18 %). The aortae of the horseshoe crab and whelk, if performing this function, have much higher energy losses, up to more than 30 % per cycle.

The microscopy studies of the aortae of the lobster, horseshoe crab and whelk revealed tissue structures which differ widely from each other as well as from the structures of the lamprey and hagfish. None of these arteries contained elastin, but all contained fibrillar material which differed in appearance, size and arrangement between species. These materials were conjectured to contribute to the elastic properties of the tissue.
Influence of Muscle Length on Work from Trabecular Muscle of Frog Atrium and Ventricle
Authors: Syme Douglas A. , Josephson Robert K.
Published: April 2021

The work capacity of segments of atrial and ventricular muscle from the frog Rana pipiens was measured as a function of muscle length using the work loop technique. Both the work done during shortening and the work required to re-lengthen the muscle after shortening increased with muscle length. Net work increased with length up to a maximum, beyond which work declined. The optimum sarcomere length for work output was 2.5–2.6 μm for both atrial and ventricular muscle.

Isometric force increased with muscle length to lengths well beyond the optimum for work output. Thus, the decline in work at long lengths is not simply a consequence of a reduction in the capacity of heart muscle to generate force. It is proposed that it is the non-linear increase in work required to re-lengthen muscle with increasing muscle length which limits net work output and leads to a maximum in the relationship between net work and muscle length.

Extension of the results from muscle strips to intact hearts suggests that the work required to fill the ventricle exceeds that available from atrial muscle at all but rather short ventricular muscle lengths.
Kinetics of Chloride Transport Across Fish Red Blood Cell Membranes
Authors: Jensen Frank B. , Brahm Jesper
Published: April 2021

The continuous flow tube method was used to investigate the kinetics of chloride transport, and its potential oxygenation-dependency, in red blood cells (RBCs) from four teleost fish species and man. A significant interspecific variation in Cl− transport kinetics was found. At 15 °C, the rate constant k for unidirectional 36Cl− efflux was significantly lower in RBCs from eel and carp than in RBCs from rainbow trout and Atlantic cod. The values of k of cod RBCs at 15 °C and of human RBCs at 37 °C were not significantly different. The volume and surface area of the RBCs were evaluated and used to calculate the apparent membrane permeability to Cl− (PCl). The magnitude of PCl followed the sequence: eel<carp<troutcod. PCl values in trout and cod at 15 °C were similar to human values at 37 °C. An extrapolation of human values to 15 °C revealed that the Cl− shift at this temperature was considerable faster in all four teleosts than in man. This illustrates appropriate adaption of band-3-mediated anion transport to the different temperature regimes encountered by fish and mammals. The Cl− transport kinetics did not differ significantly between oxygenated and deoxygenated RBCs in any of the species examined. The apparent absence of any effect of a change in haemoglobin oxygen-saturation may be related to the presence of a flexible link which results in minimal interaction between the membrane domain (mediating Cl− transport) and the cytoplasmic domain (to which oxygenation-dependent haemoglobin binding occurs) of band 3. In carp, Cl− transport kinetics were not influenced by pH over the extracellular pH (pHe) range 7.6–8.36, which spans the in vivo pHe range. The data are discussed in relation to the rate-limiting role of red blood cell HCO3−/Cl− exchange for CO2excretion.
Central Circuitry in the Jellyfish Aglantha Digitale: I. The Relay System
Authors: Mackie G. O. , Meech R. W.
Published: April 2021

The relay system is an interneuronal pathway in the margin of the jellyfish Aglantha digitale. It excites a second interneuronal pathway, the carrier system, and is itself excited by pacemaker neurones concerned with slow swimming. It also excites a slow conduction pathway in the tentacles causing graded, tonic contractions of all the tentacles during slow swimming. The pacemakers, the carrier system and the relay system all contribute to the production of excitatory postsynaptic potentials (EPSPs) in a giant axon that runs in the outer nerve ring (ring giant axon). These EPSPs may cause the latter to spike during slow swimming. If it does so, it will fire tentacle giant axons, producing twitch contractions of the tentacles. Such contractions probably help to contract the tentacles rapidly at the start of slow swimming. This is an unusual case of a giant axon that normally mediates escape behaviour being appropriated for use during a non-escape activity. The relay system can conduct impulses on its own but their conduction velocity is greatly increased when preceded by either pacemaker or ring giant spikes. This phenomenon, termed the ‘piggyback effect’, may be due to extracellular field effects rather than to actions mediated by chemical or electrical synapses. Recordings from the epithelial cells that ensheath the ring giant and outer nerve ring neurones show miniature synaptic potentials and other events that seem to reflect events in the nervous system, but no functions can be assigned to them. There is no obvious counterpart to the relay system in medusae lacking escape circuitry.
Enhanced Hypo-Osmoregulation Induced by Warm-Acclimation in Antarctic Fish is Mediated by Increased Gill and Kidney Na+ /K+ - ATPase Activities
Authors: Gonzalez-Cabrera Pedro J. , Dowd Frank , Pedibhotla Venkat K. , Rosario Rosa , Stanley-Samuelson David , Petzel David
Published: April 2021

Serum osmolality and serum inorganic ion concentrations were studied in two antarctic fish species, Trematomus bernacchii and T. newnesi, during 5 weeks of acclimation to 4 ˚C and compared with control values for groups acclimated to-1.5 ˚C. Acclimation to 4 ˚C significantly decreased the serum osmolality of both species, thereby increasing their seawater-to-extracellular fluid (ECF) osmotic gradient. The decline in osmolality with acclimation to 4 ˚C was accompanied by significant and rapid losses of Na+ and Cl− during the first 14 days of acclimation and was maintained throughout the study period. At day 35 of acclimation, the lipid composition and microsomal Na+ /K+-ATPase specific activities at 4 ˚C and 37 ˚C were determined in membranes from gill, kidney, liver and muscle tissues. No warm-induced decrease in fatty acid unsaturation was found in the tissues of either species. In the gills and kidneys of both species, the Na+ /K+-ATPase activities assayed at 4 ˚C were increased after acclimation to 4 ˚C. The Na+ /K+-ATPase activities at 37 ˚C increased at the higher acclimation temperature in T. newnesi kidneys and T. bernacchii gills, but in both species there was no compensation to temperature in the liver, regardless of assay temperature. Muscle Na+ /K+-ATPase activity decreased in response to warm-acclimation in T. bernacchii and T. newnesi assayed at 4 ˚C and 37 ˚C, respectively. During acclimation to 4 ˚C, the discontinuity in the Arrhenius plot of the Na+ /K+-ATPase activities of T. newnesi gill moved to a lower temperature, whereas that of kidney remained unchanged. The results indicate that acclimation to 4 ˚C induced a decrease in serum osmolality which resulted from the positive compensation of Na+ /K+-ATPase in osmoregulatory tissues. The enhancement in Na+ /K+-ATPase activity at 4 ˚C suggests that energy expenditure in antarctic fish may be lessened, in part, by maintaining a reduced seawater-to-ECF osmotic gradient.
Mechanical Control Of Swimming Speed: Stiffness And Axial Wave Form In Undulating Fish Models
Authors: Mchenry Matthew J. , Pell Charles A. , Long John H.
Published: April 2021

The purpose of this study was to investigate the mechanical control of speed in steady undulatory swimming. The roles of body flexural stiffness, driving frequency and driving amplitude were examined; these variables were chosen because of their importance in vibration theory and their hypothesized functions in undulatory swimming. Using a mold of a pumpkinseed sunfish Lepomis gibbosus, we cast three-dimensional vinyl models of four different flexural stiffnesses. We swam the models in a flow tank and powered them via the input of an oscillating sinusoidal bending couple in the horizontal plane at the posterior margin of the neurocranium. To simulate the hydrodynamic conditions of steady swimming, drag and thrust acting on the model were balanced by adjusting flow speed. Under these conditions, the actuated models generated traveling waves of bending. At steady speeds, the motions of the ventral and lateral surfaces of the model were video-taped and analyzed to yield the following response variables: tail-beat amplitude, propulsive wavelength, wave speed and depth of the trailing edge of the caudal fin. Experimental results showed that changes in body flexural stiffness can control propulsive wavelength, wave speed, Froude efficiency and, in consequence, swimming speed. Driving frequency can control tail-beat amplitude, propulsive wavelength, Froude efficiency, relative rate of working and, in consequence, swimming speed. Although there is no significant correlation between rostral amplitude and swimming speed, rostral amplitude can control swimming speed indirectly by controlling tail-beat amplitude and relative power. Compared with live sunfish using undulatory waves at the same speed, models have a lower Froude efficiency. On the basis of the mechanical control of swimming speed in model sunfish, we predict that, in order to swim at fast speeds, live sunfish increase the flexural stiffness of their bodies by a factor of two relative to their passive body stiffness.
Effect of Pharmacological Blockade on Cardiovascular Responses to Voluntary and Forced Diving in Muskrats
Authors: Signore Pierre E. , Jones David R.
Published: April 2021

Neural control of free and forced diving bradycardia and peripheral resistance was studied in the muskrat (Ondatra zibethicus) by means of acute pharmacological blockade with the muscarinic blocker atropine, the α-adrenergic blocker phentolamine and the β-adrenergic blockers nadolol and propranolol. Saline injection was used as a control. Heart rate in control animals increased before voluntary dives and dropped markedly as soon as the animals submerged. Heart rate started increasing towards the end of voluntary dives and reached pre-dive values within the first 5 s of recovery. Pre-dive and post-dive tachycardia were reduced in β-blocked animals, emphasizing the role of the sympathetic system during the preparatory and recovery periods of voluntary dives. Diving bradycardia and the acceleration in heart rate before surfacing were abolished by atropine and unaffected by nadolol, demonstrating the importance of vagal efferent activity during diving. The results after blockade with nadolol suggest that there is an accentuated antagonism between the two branches of the autonomic nervous system during diving, so that parasympathetic influences on the heart predominate. Propranolol-treated muskrats had a higher diving heart rate than saline-and nadolol-treated animals, which may be due to a sedative effect caused by propranolol crossing the blood–brain barrier, a blockade of central catecholaminergic pathways or a peripheral neural effect, due to the anaesthetic properties of propranolol. Phentolamine did not affect diving bradycardia, indicating that diving bradycardia occurs independently of peripheral vasoconstriction. Compared with voluntary dives, heart rate was lower before forced dives in unrestrained animals and fell to lower values during diving. Underwater endurance in forced dives was markedly reduced after atropine and phentolamine treatment (either individually or combined) compared with that of control animals. Hence, bradycardia and peripheral vasoconstriction are necessary for maximum underwater endurance. A puzzling finding was that animals without bradycardia and/or peripheral vasoconstriction still dived voluntarily for periods as long as the calculated aerobic dive limit of muskrats and survived 5 min of forcible submergence. We hypothesize that anaerobic metabolism may play an important role during diving in muskrats.
Characterization and Modulation of Na+ and Ca2+ Currents Underlying the Action Potential in Bag Cells of two Species of Aplysia
Authors: Fieber Lynne A.
Published: April 2021

The neurosecretory bag cells of Aplysia produce long trains of action potentials (afterdischarge) to release hormones important to egg laying. These ionic currents are modulated by second messengers. Modulation of excitability in bag cells is incompletely understood partly because the currents that are modulated have not been fully characterized. Whole-cell voltage-clamp experiments were executed in cultured cells from sexually mature A. californica and A. brasiliana to characterize the inward voltage-gated currents for Na+ and Ca2+. These species had similar Na+ and Ca2+ current characteristics. The Na+ currents activated at voltages less negative than -30 mV and peaked at between +10 and +20 mV in artificial sea water. The time course and pharmacology of bag cell Na+ currents were similar to those of fast Na+ current in other excitable cells. Na+ currents were abolished in Na+-free extracellular solution and were not inhibited by Cd2+. The KD for inhibition by tetrodotoxin was 2.6 nmol l−1. The Na+ current was relatively insensitive to depolarized holding potentials (Vh), maintaining approximately 65 % of peak current amplitude throughout the activation range at Vh=-30 mV. In experiments using a 1 s depolarized Vh prior to a test pulse, the half-inactivation voltage (V1/2) was -21 mV. The time constant of recovery from steady-state activation was 2.9 ms at Vh=-70 mV and 6.8 ms at Vh=-30 mV. The Ca2+ currents activated near -10 mV and peaked at approximately +20 mV with 11 mmol l-1 Ba2+ as the charge carrier. The pharmacology and V1/2 of bag cell Ca2+ current were similar to those of L-type Ca2+ currents. In extracellular solution without Na+, but containing Ba2+, Cs+ and tetraethylammonium, the Ca2+ current was inhibited by 25–100 % by nifedipine (10 µmol l−1), mean 42 %, and was unaffected in the majority of cells by w-conotoxin (10 µmol l−1). The Ca2+ current was insensitive to Ni2+ (100 µmol l−1), but was abolished by 100 µmol l−1 Cd2+. Like the Na+ current, the Ca2+ current was relatively insensitive to depolarized Vh, maintaining more than 80 % of peak current amplitude throughout the activation range at Vh=-40 mV. With a 1 s depolarized Vh prior to a test pulse, the V1/2 was -30 mV. The activation thresholds for Na+ and Ca2+ currents as well as the relative insensitivity of both currents to depolarized Vh as low as -30 mV are characteristics that would be required for spontaneous depolarizations during afterdischarge. After a 1 h treatment with phorbol 12-myristate 13-acetate (25 nmol l−1), the amplitude of Na+, Ca2+ and outward currents in individual bag cells was increased compared with control amplitudes from the same cells. Phorbol ester treatment did not change the activation and inactivation ranges, time course, V1/2 or pharmacology of the inward currents.
Enteric Reflexes and Nitric Oxide in the Fish Intestine
Authors: Karila Paul , Holmgren Susanne
Published: April 2021

The aim of the present study was to elucidate the possible regulation of peristalsis in the intestine of the Atlantic cod Gadus morhua. For this purpose, the mid intestine was dissected out and placed in a partitioned bath. Balloon distension (0.1–0.4 ml) and intramural field stimulation (8 Hz, 10 V) were carried out and the responses of the circular muscle were recorded 1.5 cm orally and anally to the stimulus using force transducers. The preparations developed spontaneous contractions propagating in the anal direction with a frequency of about one contraction per 2 min. Distension of the muscle wall with a balloon did not evoke any recordable peristaltic reflexes. Intramural stimulation caused a contraction oral to the stimulation and a relaxation anal to the stimulation in most cases. Tetrodotoxin abolished the responses to electrical stimulation in both directions. Atropine reduced and methysergide abolished the oral contractions caused by electrical stimulation. Administration of the nitric oxide synthesis inhibitor L-NG -nitro-arginine methyl ester (L-NAME) abolished the anal relaxation caused by electrical stimulation and augmented the oral contractions. The results indicate the presence in teleost fish intestine of an ascending excitatory peristaltic reflex which involves a cholinergic–serotonergic pathway and a descending inhibitory reflex involving a nitrergic pathway. These observations suggest a high degree of conservation of peristaltic mechanisms during vertebrate evolution.