bluuebunny/crossref_metadata_2025_split huggingface dataset:
Extraocular Sensitivity to Polarized Light in an Echinoderm
Authors: Johnsen Sönke 
Published: April 2021

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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&lt;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

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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&lt;carp&lt;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

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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.