bluuebunny/crossref_metadata_2025 huggingface dataset:
Production of Oestrogenic Substance by the Bird Testis
Authors: Callow R. K. , Parkes A. S.
Published: April 2021

Oestrogenic substances are now known to be elaborated and excreted by the males of various species of mammals. The testes and urine of the stallion (Zondek, 1934), in particular, and the testes of the hog and bull (Courrier, 1934) contain notable amounts of oestrogenic compounds. In the case of the horse, the urine is relatively inactive in castrates (viz. geldings), so that it may be assumed that the testis is the origin of this oestrogenic material. Oestrone is isolated from stallion’s urine after mild chemical treatment, and it would appear that, whilst oestrone may not occur as such in the urine, the primary oestrogenic material in the stallion is a simple derivative of oestrone.
Water Permeability of Palaemon Longirostris and other Euryhaline Caridean Prawns
Authors: Campbell Peter J. , Jones M. B.
Published: April 2021

Water permeability [based on the half-time of exchange of body water with the environment (T1/2)] of the upper estuarine prawn Palaemon longirostris was measured in a range of salinities at 4, 12 and 20°C. Prawns acclimated for 7 days were compared with prawns exposed to acute salinity changes. Acclimation to low salinity and low temperature caused a significant reduction in permeability. Transfer of prawns from 34 to 0.5 ‰ had no immediate effect on permeability; however, transfer from 0.5 to 34 ‰ caused an immediate significant rise in permeability. Heart rate of P. longirostris acclimated to 0.5 and 34 ‰ at 4, 12 and 20°C was unaffected by salinity, but was significantly reduced at low temperature.

The permeabilities of three other prawn species (Palaemonetes varians, Crangon crangon and Palaemon elegans), which have different horizontal distributions in estuaries and different salinity tolerance ranges, were also studied and compared with the values obtained for P. longirostris. P. varians and C. crangon showed significantly reduced permeabilities at low compared with high salinities; however, the permeability of P. elegans was unchanged at the two salinities used for this species (22 and 34 ‰). At each experimental salinity, permeabilities followed the sequence: P. longirostris<P. varians<C. crangon<P. elegans. Results show that reduction of permeability is an important physiological adaptation to life in dilute saline regions and may be involved in separating species with overlapping salinity tolerance ranges.
Effect of Variation in Form on the Cost of Terrestrial Locomotion
Authors: Full Robert J. , Zuccarello Daniela A. , Tullis Alexa
Published: April 2021

The mass-specific minimum cost of terrestrial locomotion (Cmin) decreases with an increase in body mass. This generalization spans nearly eight orders of magnitude in body mass and includes two phyla. The general relationship between metabolic cost and mass is striking. However, a significant amount of unexplained interspecific variation in Cmin exists at any given body mass. To determine how variation in morphology and physiology affects metabolic energy cost, we measured the oxygen consumption of three comparably sized insects running on a miniature treadmill; the American cockroach Periplaneta americana, the caterpillar hunting beetle Calosoma afline and the Australian field cricket Teleogryllus commodus. Steady-state oxygen consumption increased linearly with speed. Cmin was similar for crickets and cockroaches (8.0 and 8.5mlO2g−1km−1, respectively), but was substantially lower for beetles (4.6ml O2 g−1km−1). The predicted value of Cmin for all three insects was within the 95% confidence intervals of the Cminversus body mass function. However, the 95% confidence intervals extend approximately 2.5-fold above and 40 % below the regression line, making the variation at any given body mass nearly sixfold. Normalizing for the rate of muscle force production by determining the metabolic cost per stride failed to account for the interspecific variation in the cost of locomotion observed in the three insects. Ground contact costs (i.e. multiplied by leg contact time during a stride) in insects were similar to those measured in mammals (1.5–3.1 J kg−1) and were independent of speed, but did not explain the interspecific variation in the cost of locomotion. Muscles of the caterpillar hunting beetle may have a greater mechanical advantage than muscles of the Australian field cricket and American cockroach. Variation in musculo-skeletal arrangement, apart from variation in body mass, could translate into significant differences in the minimum cost of terrestrial locomotion.
Effects of prestretch at the onset of stimulation on mechanical work output of rat medial gastrocnemius muscle-tendon complex
Authors: Ettema G. J. , Huijing P. A. , van Ingen Schenau G. J. , de Haan A.
Published: April 2021

Work output of rat gastrocnemius medialis (GM) muscle (N=5) was measured for stretch-shortening contractions, in which initiation of stretch occurred prior to the onset of activation, and for contractions with an isometric prephase. Duration of the active prephase (prestretch and pre-isometric) varied from 20 to 200 ms. Subsequent shortening (from optimum length+4 mm to optimum length-2 mm) lasted 150 ms. Stretch velocities of 5, 10 and 20mms−1 were used, and the shortening velocity was 40mms−1. The effects of several combinations of active stretch duration and active stretch amplitude were compared. Using forcecompliance characteristics, the work of the contractile element (CE), elastic energy storage and release of the undamped series elastic component (SEC) were distinguished. During shortening, an extra amount of work output was produced, induced by active stretch, of which the largest contribution (70–80%) was due to higher elastic energy release. Enhancement of the storage and utilization of elastic energy during the stretch-shortening cycle, caused by higher transition-point forces (i.e. force at onset of shortening), increased with active stretch amplitude and was associated with a net loss of work, probably due to cross-bridge detachment during active stretch. Net work over the stretch-shortening cycle remained positive for all prestretch contractions, indicating that when a muscle performs this type of contraction, it is able to contribute to work performance on body segments. It is concluded that, in stretch-shortening movements of rat GM muscle, maximal positive work output is incompatible with maximal net work output. Consequences for complex movements in vivo are discussed.
Activity of the hypaxial muscles during walking in the lizard Iguana iguana
Authors: Carrier D.
Published: April 2021

The role that the hypaxial muscles play in locomotion has been largely ignored by biologists. In tetrapods, there are at least three possibilities. First, the hypaxial muscles might bend the trunk laterally to increase stride length. Second, they might stabilize the trunk against the horizontal, lateral and vertical components of the propulsive force. Alternatively, they might not be involved in locomotion. This study evaluated these three hypotheses by analyzing the activity of the hypaxial muscles of green iguanas (Iguana iguana). During walking, the rectus abdominis, obliquus externus superficialis and profundus, intercostales externi, and ventral portion of the intercostales interni on one side of the trunk acted synergistically with the lateral portion of the intercostales interni and obliquus internus on the other side of the trunk. This pattern supports the hypothesis that the hypaxial muscles act to stabilize the trunk during locomotion. Specifically, the longitudinally oriented rectus abdominis, obliquus externus profundus and ventral portion of the intercostales interni appear to stabilize the trunk against the horizontal and lateral components of the propulsive force, which tend to rotate the girdles in the horizontal plane. The obliquely oriented obliquus externus superficialis, intercostales externi, lateral portion of the intercostales interni and obliquus internus appear to stabilize the trunk against the vertical component, which induces long-axis torsion in the trunk. Thus, the demands of locomotion may provide a functional explanation for the basic organization of the hypaxial muscles of tetrapods.
Properties of potassium currents and their role in membrane excitability inDrosophilalarval muscle fibers
Authors: Singh S. , Wu C. F.
Published: April 2021

The larval muscle fibers of Drosophila show four outward K+ currents in addition to the inward Ca2+ current in voltage-clamp recordings. The Shaker (Sh) and the slowpoke (slo) mutations, respectively, eliminate the voltage-activated fast K+ current (IA) and the Ca2+-activated fast K+ current (ICF)-Quinidine specifically blocks the voltage-activated delayed K+ current (IK) at micromolar concentrations. We used Sh, slo and quinidine to remove specifically one or more K+ currents, so as to study physiological properties of these currents not previously characterized, and to examine their role in membrane excitability. A linear relationship was observed between the peak ICF and the peak Ica at different membrane potentials. ICF inactivated considerably during a 140ms pulse to +20 mV. Recovery from inactivation was not complete for up to 2 s at the holding potential of −50 mV, which is much slower than the recovery of Ca2+ current from inactivation. In addition to IA and ICF, two delayed K+ currents are also observed in these fibers, the voltage-activated IK and the Ca2+-activated Ics-Near the end of a 500 ms depolarizing pulse, both IA and ICF are inactivated. Ca2+-free and 20 mmol 1−1 Ca2+ saline were used to examine the tail currents of the remaining IK and Ics-The tail currents of Ics were slower than those of IK and reversed between −30 and −50mV in different fibers. We further studied the dose-dependence of the blockade of IK by quinidine, which did not indicate a simple one-to-one binding mechanism. Current-clamp recordings from normal, Sh, slo and the double-mutant Sh;slo fibers suggested that ICF plays a stronger role than IA in repolarization of the larval muscle membrane. Elimination of ICF facilitates the occurrence of action potentials. Further elimination of IK prolonged the action potentials to several hundred milliseconds.
An Examination Of Central Chemosensitivity In An Air-Breathing Fish (Amia Calva)
Authors: Hedrick M. S. , Burleson M. L. , Jones D. R. , Milsom W. K.
Published: April 2021

The role of central chemosensitivity in the control of ventilation in fishes was investigated directly by perfusing a mock extradural fluid (EDF) through the cranial space in the medullary region of conscious air-breathing fish, Amia calva. Perfusions with Sudan Black dye showed that the mock EDF communicated with the cerebrospinal fluid (CSF) and entered the cerebral ventricles. Altering the , and/or pH of the mock EDF had no effect on gill- or air-breathing rates, heart rate or blood pressure during exposure to normoxic water. Aquatic hypoxia, however, stimulated gill ventilation and elevated blood pressure, but did not affect heart rate; altering the gas tensions and/or pH of mock EDF still had no effect on recorded variables. Sodium cyanide (NaCN) added to the mock EDF caused struggling at concentrations above 500μ gml − 1, but did not uniformly stimulate ventilation. These results suggest that central chemoreceptors, which mediate cardiovascular or ventilatory reflexes, are absent in Amia.
Prey Capture and the Fast-Start Performance of Northern Pike Esox Lucius
Authors: Harper David G. , Blake Robert W.
Published: April 2021

Fast-start performance of northern pike Esox lucius (mean length, 0.38m) during prey capture was measured with subcutaneously implanted accelerometers. Acceleration-time plots and simultaneous high-speed ciné films reveal four behaviours with characteristic kinematics and mechanics. The fast-start types are identified by the number of large peaks that appear in the acceleration-time and velocity-time data.

Comparisons of mean performance were made between each type of feeding fast-start. Type I fast-starts were of significantly shorter duration (0.084 s) and displacement (0.132 m) than type III (0.148 s and 0.235 m) and type IV (0.189 s and 0.306m) behaviours, and higher mean and maximum acceleration (38.6 and 130.3ms− 2, respectively) than type II (26.6 and 95.8ms− 2), type III (22.0 and 91.2ms− 2) and type IV (18.0 and 66.6ms− 2) behaviours. The type II behaviours were of shorter duration (0.115 s) and displacement (0.173 m) and of higher mean acceleration than type IV fast-starts, and were also of significantly shorter duration than type III behaviours.

Prey-capture performance was compared to escapes by the same individuals. When data are combined, regardless of mechanical type, mean acceleration (37.6 vs 25.5 ms− 2), maximum acceleration (120.2 vs 95.9 ms− 2), mean velocity (1.90 vs 1.57 m s− 1) and maximum velocity (3.97 vs 3.09 ms− 1) were found to be larger and duration shorter (0.108 vs 0.133s) during escapes than during prey capture. No differences were found through independent comparisons of the performance of feeding and escape types II and III, but type I escapes had significantly higher mean velocity (2.27 vs 1.58ms− 1), maximum velocity (4.70 vs 3.12ms− 1) and mean acceleration (54.7 vs 38.6 ms− 2) than type II feeding behaviours.

Prey-capture performance was also related to prey size, apparent prey size (defined as the angular size of the prey on the pike’s retina) and strike distance (the distance from the pike to the prey at the onset of the fast-start). Mean and maximum acceleration increased with apparent size and decreased with strike distance, while the duration of the event increased with strike distance and decreased with apparent size. No relationship was found between the actual prey size and any performance parameter.

Strike distance ranged from 0.087 to 0.439 m and decreased as the apparent size increased from 2.6 to 9.9° (r2=0.75). The type I behaviour was usually employed when the strike distance was small and the prey appeared large. As strike distance increased and apparent size decreased, there was a progressive selection of type II, then III and then IV behaviours.
Potassium and Calcium Currents in Dissociated Muscle Fibres of the Mollusc Philine Aperta
Authors: Dorsett D. A. , Evans C. G.
Published: April 2021

Dissociated unstriated muscle fibres from the buccal mass retractor muscles of the mollusc Philine aperta were studied using a two-electrode voltage-clamp. The mean resting potential of the fibres was –76.3±0.44mV (N=30), and the membrane resistance was 42.2±3MΩ. The space constant of the fibres was 2.03±0.33mm (N=5).

Three outward potassium currents were resolved in response to a depolarising step to zero from resting potential. (1) An early transient current, voltage-activated and blocked by 2 mmol I−1 4-aminopyridine (4-AP). This resembled the A-current described in molluscan neurones and some arthropod muscle fibres. (2) A calcium-dependent late transient current, with slower kinetics, which was suppressed by 50 mmol 1−1 tetraethylammonium chloride (TEA–CI), zero-calcium saline, 1 mmol E1 Cd2+ and 1 μmol I−1 verapamil. (3) A delayed voltage-activated current, blocked by 50 mmol I−1 TEA-CI and with kinetics associated with the delayed rectifier current IK.

An inwardly directed current, blocked by zero-calcium salines, Cd2+ and verapamil, was considered to be a calcium current whose activation closely matched that of the Ca2+-dependent potassium current.

A blockade of either the A-current, or exposure to low-calcium artificial sea water, or a combination of both, promoted the development of oscillations and regenerative spikes in the muscle fibre following depolarization.
The Relation Between Growth and Food Consumption in the Brown Trout (Salmo Trutta)
Authors: Pentelow F. T. K.
Published: April 2021

The relation between the amount of food consumed and the growth made is one of considerable ecological importance, though the study of it has hitherto been confined almost entirely to domesticated animals living on artificial foods. In the case of fishes there is a good deal of information available in American and German literature on the food requirements of fish in fish farms and hatcheries but practically none on the relation between the amount of natural food eaten and the growth rate. Dawes (1930–1) studied this relation for the plaice, using chopped mussel (Mytilas edulis) as food, and recently Surber (1935) has described an experiment, similar to those on which this paper is based, on feeding brook trout (Salvelinus fontinalis) and rainbow trout (Salmo gairdneri) with Gammarus fasciatus.
Comparative Measurements of Water and Electrolyte Exchange in A Stenohaline and in A Euryhaline Polychaete
Authors: Ellis W. G.
Published: April 2021

Nereis diversicolor (Müller) is a euryhaline polychaete. In brackish water it is able to “regulate” the water exchange between body fluid and environment. The related stenohaline species Perinereis (Nereis) cultrifera (Grube) has no such powers of regulating its water exchange, which differs from that of Nereis diversicolor in two respects: (1) in. brackish water of a given osmotic pressure the initial water intake is much larger than that of N. diversicolor, relative to the body weight; (2) there is no subsequent water loss (Beadle, 1931).
The Activity of the Spermatozoa of Salmo Salar in Relation to Osmotic Pressure
Authors: Ellis W. G. , Jones J. W.
Published: April 2021

Artificial insemination of trout eggs gives a higher proportion of fertilized eggs than natural fertilization. This paradoxical fact is explained by the very brief time of activity of the sperm in river water (Gray, 1920). Huxley (1930) showed that the activity of trout sperm is increased in various salt solutions, and concluded that the trout “though somatically fully adapted to fresh-water life, is very imperfectly adapted in its reproduction, its sperms being many times more efficient in a medium intermediate between its present and its ancestral environment”.
Exercise In Birds
Authors: Butler P. J.
Published: April 2021

Birds have two independent locomotor systems: the forelimbs (wings) are used predominantly for aerial flight, but may be used for underwater propulsion, e.g. in penguins; the hindlimbs (legs) are used for running, surface swimming and diving. In birds of similar mass, energy consumption during flight is approximately 2.5 times greater than that when running or swimming at maximum speed. This difference is the result not only of the larger mass of the flight muscles compared with that of the leg muscles, but also of their greater oxidative capacity. Interestingly, the relationship of energy consumption to body mass in cursorial birds when running is similar to that of volant birds when flying. Energy consumption during diving may be as high in some birds (e.g. tufted duck) as when they are swimming at maximum sustainable speed, and this is not influenced by water temperature.

The composition of the flight and leg muscles is different. The muscles of the leg consist of deeply situated slow oxidative (SO) fibres, which are active during quiet standing and walking, fast oxidative glycolytic (FOG) fibres, which are recruited during walking and sustained running or swimming, and peripherally located fast glycolytic (FG) fibres, which are recruited at the highest running or swimming speeds. In most volant birds, the pectoralis muscle consists predominantly of FOG fibres with a smaller percentage of FG fibres. There is some controversy over the occurrence of SO fibres in some species, although they are most probably present in those that glide. The FOG fibres are highly oxidative, with a high capillary density.

The respiratory and cardiovascular adjustments that occur during flying, running and diving are described, and the ability of some species of birds to fly at extremely high altitudes, where the partial pressure is one-third of the sea level value, is discussed.
Acid-Base and ion Balance, Metabolism, and Their Interactions, After Exhaustive Exercise in Fish
Authors: Wood Chris M.
Published: April 2021

In fish, exhaustive exercise stress differs from steady-state aerobic exercise in causing (1) a depletion of glycogen, creatine phosphate (CP) and ATP reserves and an accumulation of lactate and metabolic acid in white muscle; (2) blood respiratory and metabolic acidoses ( and elevations, respectively); (3) marked ionic and fluid volume disturbances; and (4) a surge in plasma catecholamines. During recovery, the smaller fast component (20%) of excess postexercise oxygen consumption (EPOC) is explained by CP and ATP resynthesis and aerobic demands, but the larger slow component (80%) is considerably greater than the cost of lactate clearance and glycogen resynthesis. Ionic and H2O shifts may contribute significantly to EPOC; net fluxes are greatest between extracellular (ECF) and intracellular fluid (ICF) compartments, with smaller disturbances at the kidney (increased filtration, reabsorption and excretion) and gills (passive ion losses and H2O uptake). Modulation of branchial Na+ and Cl− exchange is important in the temporary storage of in the environment during recovery. Movements of lactate and , from ICF to ECF are dissociated processes; the major portions of both are retained in the white muscle and are probably cleared by oxidation and/or glycogen resynthesis in situ. Elevated catecholamine levels are implicated in many of these responses and serve to protect metabolic processes against acid-base disturbances, but do not appear to contribute to EPOC directly. Catecholamines also cause an elevation in blood by a mechanism linked to the β-adrenergic activation of red blood cell Na+/H+ exchange that protects O2 transport. The compound blood acidosis stimulates ventilation to meet the demands of EPOC.
Intrinsic Mechanisms Controlling Cardiac Stomach Volume of the Rainbow Trout (Oncorhynchus Mykiss) Following Gastric Distension
Authors: Grove David J. , Holmgren Susanne
Published: April 2021

Inflation of the cardiac stomach of the rainbow trout induced reflex muscular contractions. The stomach then slowly relaxed asymptotically towards its maximum volume. Continued distension caused the stomach to become compliant and this was irreversible within the time course of each experiment (8h). Repeated periods of rest and distension revealed a short-term inhibition of reflex contractions which recovered as resting periods were extended. Sectioning the vagosympathetic trunk did not influence the response to distension. Similar responses occurred in isolated, perfused stomachs. Both tetrodotoxin and atropine plus methysergide induced immediate compliance, suggesting that it was caused by the blockade of enteric excitatory neurones. Atropine alone primarily reduced reflex contractions whilst methysergide completed this suppression and induced profound gastric relaxation. Somatostatin reversibly suppressed reflex contractions whilst vasoactive intestinal polypeptide (VIP) induced gastric relaxation. A model is proposed in which distension initially causes reflex activity via cholinergic and serotonergic nerves, whilst gastric tone remains high. Somatostatin then suppresses rhythmic contractions, whilst VIP suppresses the tryptamin-ergic mechanisms that maintain gastric tone. The rainbow trout stomach possesses intrinsic mechanisms that mimic the extrinsic, nerve-controlled ‘receptive relaxation’ or ‘accommodation’ that follows feeding in higher vertebrates.
Opposite Actions of the Anthozoan Neuropeptide Antho-Rnamide on Antagonistic Muscle Groups in Sea Anemones
Authors: McFarlane Ian D. , Reinscheid Rainer K. , Grimmelikhuijzen Cornelis J. P.
Published: April 2021

Coelenterates are generally assumed to be primitive animals with simple nervous systems. We believe, however, that in at least one group, the sea anemones, the nervous system is in reality rather complex, a view supported by the growing number of neuropeptides recently extracted from these animals (Grim-melikhuijzen et al. 1990a,b). Three of these peptides (Antho-RFamide and the Antho-RWamides I and II) have demonstrable physiological actions on sea-anemone muscle preparations (McFarlane et al. 1987, 1990; McFarlane and Grimmelikhuijzen, 1991) and, in the case of the Antho-RWamides, on isolated muscle cells (McFarlane et al. 1991). Here we consider a fourth neuropeptide from sea anemones, Antho-RNamide (L-3-phenyllactyl-Leu-Arg-Asn-NH2) (Grim-melikhuijzen et al. 1990), and show that it has opposite actions on adjacent antagonistic muscles in sea anemones.
Membrane Potential Responses to Thermal Stimulation and the Control of Thermoaccumulation in Paramecium Caudatum
Authors: Tominaga Takashi , Naitoh Yutaka
Published: April 2021

The overall membrane potential response of the ciliate Paramecium caudatum to a rise in the temperature of its environment was depolarizing when the ambient temperature before stimulation (Te) was equal to or higher than the culture temperature (Tc), but hyperpolarizing when Te was lower than Tc. The anterior region of the cell responded to a rise in temperature with a localized membrane depolarization. The posterior region was depolarized when Te was equal to or higher than Tc, but hyperpolarized when Te was lower than Tc. The Te-dependent polarity reversal of the posterior response was responsible for the comparable reversal of the overall response. The temperature at which the polarity reversal of the posterior response took place shifted according to Tc. This shift caused a comparable shift in the temperature at which polarity reversal occurred for the overall response. The Tc -dependent polarity reversal of the posterior response and its Tc-dependence are major causes of thermoaccumulation mediated by ciliary activity of Paramecium in regions with temperatures close to Te.
The Potentiating Effect of Prestretch on the Contractile Performance of Rat Gastrocnemius Medialis Muscle During Subsequent Shortening and Isometric Contractions
Authors: Ettema G. J. C. , Huijing P. A. , De Haan A.
Published: April 2021

The aim of the present study was to investigate the effect of an active stretch during the onset of a muscle contraction on subsequent active behaviour of the contractile machinery within an intact mammalian muscle-tendon complex. Muscle length and shortening velocity were studied because they may be important variables affecting this so-called prestretch effect. Seven gastrocnemius medialis (GM) muscles of the rat were examined. Tetanic, isovelocity shortening contractions from 3 mm above muscle optimum length (l0) to l0—2 mm, at velocities of 10–50mm s-1 (dynamic experiments), were preceded by either an isometric contraction (PI) or an active stretch (PS). By imposing quick length decreases between the prephase and the concentric phase, all excess force generated in the prephase was instantaneously eliminated. This procedure only allowed small force changes during subsequent shortening (caused by the intrinsic properties of the contractile machinery). In this way, the influence of series elastic structures on subsequent muscle performance was minimized. Experiments were also performed at lengths ranging from l0+2.5mm to l0–1.5 mm, keeping the length constant after the initial quick length changes (isometric experiments). For the dynamic experiments, enhancement of the performance of the contractile machinery (potentiation) was calculated as the ratio of the average force level over each millimetre of shortening during PS to that during PI conditions (PS/PI). For the isometric experiments, the PS/PI force ratio after 300 ms of stimulation was used.

The main result of the present study confirmed results reported in the literature and experiments on isolated muscle fibres. For all conditions, a potentiation effect was found, ranging from about 2 to 16 %. Muscle length appeared to have a large positive effect on the degree of potentiation. At the greatest lengths potentiation was largest, but at lengths below optimum a small effect was also found. A negative influence of shortening velocity was mainly present at increased muscle lengths (l0+2.5 mm and l0+1.5 mm). For the dynamic experiments, no interaction was found between the effects of muscle length and shortening velocity on potentiation. However, there was a clear difference between the isometric and dynamic responses: the dependence of potentiation on muscle length was significantly greater for the isometric contractions than for the dynamic ones. These isometric-dynamic differences indicate that the processes underlying prestretch effects operate differently under isometric and dynamic conditions. The conditions under which the experiments were performed allow us to suggest that the potentiation effects described here might play an important role in ballistic movements containing active stretch periods (e.g. countermovement jumping).
Insect Cardioactive Peptides: Regulation of Hindgut Activity by Cardioacceleratory Peptide 2 (Cap2) During Wandering Behaviour In Manduca Sexta Larvae
Authors: Tublitz N. J. , Allen A. T. , Cheung C. C. , Edwards K. K. , Kimble D. P. , Loi P. K. , Sylwester A. W.
Published: April 2021

The functional relationship between cardioacceleratory peptide 2 (CAP2) and hindgut activity during wandering behaviour was investigated in fifth-instar larvae of the tobacco hawkmoth Manduca sexta. Inspection of the alimentary canal on the day prior to wandering showed that the gut, in preparation for metamorphosis, was voided of all contents by 18:00 h. Associated with this event, which we refer to as ‘gut emptying’, was an increase in the frequency of hindgut contractions measured in vivo. No change in heart activity was seen during this developmental period. Measurements of the amount of CAP2 in the central nervous system (CNS) of fifth-instar caterpillars revealed that CAP2 storage levels declined sharply on the day of gut emptying. The drop in CNS levels of CAP2 at gut emptying was temporally correlated with the appearance of CAP2 in the haemolymph. CAP2, when applied at physiological concentrations to an in vitro larval hindgut bioassay, caused changes in several parameters, including contraction frequency and amplitude, and basal tension. In vivo administration of CAP2 elicited hindgut responses that were qualitatively and quantitatively similar to those seen in vitro. Developmental studies on changes in CAP2 responsiveness during the last larval instar demonstrated that the hindgut is maximally sensitive to CAP2 on the day of gut emptying. Direct evidence in support of a role for CAP2 in fifth-instar larvae was provided by experiments in which the increase in gut activity in vivo seen at gut emptying was significantly reduced by injections of an anti-CAP antibody. Based on data from cobalt backfills and anti-CAP immunohistochemical staining, we propose that CAP2 exerts its effect on the larval hindgut at wandering via a local release from CAP-containing neurones in the terminal ganglion that project directly to the hindgut.
Dicyclohexylcarbodiimide Reacts Specifically with The 16 kDa Subunit of Larval Manduca Sexta Midgut Vacuolar-Type Atpase
Authors: Zheng X. Y. , Spaeth D. D. , Harvey W. R. , Wolfersberger M. G.
Published: April 2021

Proton-motive vacuolar-class ATPases (V-ATPases) are commonly associated with membrane-bound organelles other than mitochondria and chloroplasts. They are found in the vacuoles of Neurospora crassa and yeasts, in tonoplasts of plants and in endomembranes such as lysosomes, endosomes, clathrin-coated vesicles and secretory granules (Sze, 1985; Rudnick, 1986; Mellman et al. 1986; Rodman et al. 1991). However, they have also been found in plasma membranes of kidney tubules (Brown et al. 1987; Wang and Gluck, 1990). Recently, the pump responsible for the large lumen-directed net flux of potassium across larval Manduca sexta midgut has been shown to consist of a plasma membrane protonmotive V-ATPase functioning in conjunction with an nH+/K+ antiporter (Wieczorek et al. 1991).
Disk-Sphere Transformation in Mammalian Red Cells
Authors: Furchgott Robert F.
Published: April 2021

The purpose of this paper is to try to explain the phenomenon of the transformation of the mammalian erythrocytes from disks to spheres when a small drop of a saline suspension is placed between glass slide and cover-glass. Ponder (1934) several years ago reviewed the work which had been done in connexion with this phenomenon. As was pointed out by Ponder, who was the first to show clearly the necessity of having the glass surfaces in close proximity for the formation of perfect spheres (1928-9), the two explanations which have been put forth to explain the phenomenon are both inadequate. As will be seen later, that of Waller (1930) is somewhat closer to the true explanation than that of Brinkman & van Dam (1920).
STRUCTURAL AND METABOLIC CHARACTERIZATION OF THE MUSCLES USED TO POWER RUNNING IN THE EMU (DROMAIUS NOVAEHOLLANDIAE), A GIANT FLIGHTLESS BIRD
Authors: Patak A. , Baldwin J.
Published: April 2021

The emu is a giant flightless bird, capable of sustained high-speed running. Anatomical, histochemical and biochemical properties of the lower leg muscles used to power running were investigated. The gastrocnemius is the largest muscle in the emu leg. It has a short inelastic tendon and contains only fast fibres. It is the major power-producing muscle of the lower leg, with a greater capacity than the digital flexor muscles for bursts of high work output. In marked contrast, the digital flexors have long elastic tendons and contain both fast and slow muscle fibres. It is proposed that these muscles, rather than the gastrocnemius, are responsible for maintaining posture and that they facilitate elastic energy storage and retrieval in their tendons during running. In comparison with equivalent muscles of flying and diving birds, emu lower leg muscles display features consistent with greater power output during both short burst and endurance running. The emu muscles are more massive relative to body size, and the gastrocnemii of other birds invariably contain slow fibres This study illustrates some of the similarities as well as differences between muscles used during flying and running. Capacities for sustained high-energy work appear to be similar in flying birds and running emus as judged from (1) the muscle masses used during locomotion when expressed as a proportion of total body mass and (2) muscle fibre type compositions and their potential for fuel catabolism. The lower creatine kinase activity in emu leg muscles could be attributed to higher energy demands during the initial stages of lift-off for flight.
Chloride-Dependent Organic Phosphate Sensitivity of the Oxygenation Reaction in Crocodilian Hemoglobins
Authors: Weber Roy E. , White Fred N.
Published: April 2021

We show that crocodilian hemoglobins (Hbs), which previously have been considered to be model pigments lacking allosteric interaction with organic phosphate esters, do exhibit oxylabile ATP and 2,3-diphosphoglycerate (DPG) binding that decreases O2 affinity and increases pH sensitivity (Bohr effect), in the absence of Cl−and at the low Cl−concentrations that may occur in crocodilian plasma during ‘post-ingestive alkaline tides’. Hbs from different species vary in their phosphate sensitivities. In Alligator mississippiensis Hb, O2 affinity shows greater ATP than DPG sensitivity at low [cofactor]/[Hb] ratios. In Paleosuchus palpebrosus Hb, where even a high Cl−concentration (0.1 mol l−1) does not completely suppress the phosphate effects, the opposite is true, whereas both ATP and DPG exert similar effects in Caiman crocodilus Hb. Lactate, at concentrations that may occur after intensive exercise, similarly depresses Hb O2-affinity, indicating an O2 demand/O2 supply feedback regulation. Curiously, inositol hexaphosphate (IHP), a potent allosteric effector in other vertebrate Hbs, has no effect on A. mississippiensis and P. palpebrosus Hb and only small effects on C. crocodilus Hb, presumably because of steric hindrance at the binding site. The molecular mechanisms underlying the observations (particularly the implication of β82-Lys, i.e. the lysine residue at position 82 of the β-chains that binds phosphate and Cl−) are considered. Their physiological significance requires further study.
The Effects of Hypoxia, Hyperoxia or Hypercapnia on the Acid–base Disequilibrium in the Arterial Blood of Rainbow Trout
Authors: Gilmour Kathleen M. , Perry Steve F.
Published: April 2021

An extracorporeal circulation in combination with a stop–flow technique was used to characterize the acid–base disequilibrium in the arterial blood of rainbow trout Oncorhynchus mykiss during environmental hypoxia, hyperoxia or hypercapnia. Arterial blood was routed from the coeliac artery through an external circuit in which pH (pHa), partial pressure of oxygen and partial pressure of carbon dioxide were monitored continuously. The stop–flow condition was imposed by turning off the pump which drove the external loop. Water or was adjusted to give the experimental conditions by bubbling N2, O2 or CO2 through a water equilibration column supplying the fish.

During normoxia, the arterial blood exhibited a positive acid–base disequilibrium of approximately 0.04 pH units; that is, pH increased over the stop–flow period by 0.04 units. The extent of the imbalance was increased significantly by hypoxia (final =2.7–3.7 kPa; pH=0.05 units). In fish exposed to hyperoxia (final =47–67 kPa), the direction of the disequilibrium was reversed; pHa declined by 0.03 units. During hyperoxia, CO2 excretion was impaired by 63% and the of postbranchial blood was higher than that of prebranchial blood. It is therefore conceivable that a reversal of the normal, outwardly directed, diffusion gradient for CO2 accounted for the negative disequilibrium; CO2 uptake at the gills would drive plasma CO2/HCO3−/H+ reactions towards CO2 hydration and H+ formation. During hypercapnia, fish exhibited a twofold increase in the positive pH disequilibrium (ΔpH=0.06 units).

The results of this study confirmed the existence of an acid–base disequilibrium in the arterial blood of rainbow trout and clearly demonstrated that the extent and/or direction of the disequilibrium are influenced by the respiratory status of the fish.
Evidence for Hydration-Dependent Closing of Pore Structures in the Cuticle of Periplaneta Americana
Authors: Machin J. , Smith J. J. B. , Lampert G. J.
Published: April 2021

Integumental electrical resistances were measured on the antenna, pronotum, forewing, second abdominal tergite, fifth abdominal sternite and the femur of the third leg in restrained male and female Periplaneta americana. The same measurements, excepting those on antenna and wing, were made on last-instar nymphs. Electrical contact was made through two externally applied glass tubes filled with cockroach Ringer with a combined contact area of about 2 mm2. Resistances corresponding to current flows through two thicknesses of integument were measured using a current-clamping amplifier. Calculated electrical conductances tended to be higher in the antennae, pronotum and abdominal tergites than in the legs and wings. Conductances of the pronotum and abdominal tergites were significantly higher (P<0.001) in males than in females. The literature suggests that male abdominal tergites are the site of sex pheromone production. In nymphs as well as adults, the conductances of all areas, except the antennae of males, decreased following dehydration and a decline in animal water content. In most cases the magnitude of the decrease was tightly correlated with initial hydrated conductance. The data suggest that variations in regional conductances in hydrated animals are principally due to differences in dermal gland density. We argue that the decrease in conductance following dehydration is evidence of a mechanism closing dermal gland openings in times of water stress.
Physical Properties Of Gametes In Three Sea Urchin Species
Authors: Thomas Florence I. M.
Published: April 2021

Physical properties (density in kg m-3, viscosity, sinking rates and dispersion rate) of the gametes and associated spawned materials were measured for three species of sea urchin, Tripneustes gratilla, Echinometra mathaei and Colobocentrotus atratus, from habitats that differ in wave exposure. The gametes of all three species are negatively buoyant, highly viscous and exhibit shear-thinning (a decrease in viscosity with increasing shear rate). Female gametes are more viscous than male gametes, and the viscosity of female gametes differs among the three species. The viscosity of female gametes is highest for C. atratus, the species from habitats most exposed to wave action. Within the species T. gratilla, viscosity of female gametes is higher in habitats exposed to wave action than in more protected habitats.

Evidence reported in this paper suggests that the shear-thinning of gametes may provide a performance advantage for these sea urchins. High viscosity of gametes at low shear rates may decrease gamete dispersal upon release and, under certain flow conditions, allow gametes to form strings and clumps on the surface of the urchin. Depending upon the morphology of the surface, these clumps or strings may be retained and fertilization may occur within these clumps or strings. Conversely, low viscosity of gametes at high shear rates decreases the power required to extrude gametes through the gonoduct during spawning.
Effect Of Mechanical Vibration On Active Tension In The Longitudinal Retractor Muscle Of A Sea Cucumber Stichopus Japonicus
Authors: Kobayashi T. , Ushitani H. , Wada H. , Inoue J. , Kawakami T. , Sugi H.
Published: April 2021

The effect of mechanical vibration on active tension in an echinoderm somatic smooth muscle was studied using the longitudinal retractor muscle (LRM) of a sea cucumber Stichopus japonicus. VBThe steady contracture tension in LRM fibres maximally activated with 10−3 mol l−1 acetylcholine (ACh) was reduced by vibrations (peak-to-peak amplitude, 0.5–2.5% of l0, where l0 is the slack length of the muscle; frequency, 5–100 Hz). The extent of reduction of active contracture tension increased with increasing amplitude of vibration, but it did not change appreciably with increasing frequency of vibration. The steady contracture tension in LRM fibres submaximally activated with 10−5 mol l−1 ACh was more markedly reduced by vibrations than was that in maximally activated fibres. The vibration-induced reduction of active contracture tension disappeared when temperature was lowered from 20–23 to 0°C. The development of contracture tension in LRM fibres activated with ACh was not affected by mechanical vibration. These results are discussed in connection with the vibration-induced decrease in the rate of breakage of the actin–myosin linkages responsible for isometric force generation.
Extreme Drag Forces and the Survival of Wind-and Water-Swept Organisms
Authors: Denny Mark W.
Published: April 2021

A stationary organism exposed to steady turbulent flow is subjected to a drag force that fluctuates about a mean, and when the drag on the organism is characterized, it is traditionally this mean force that is cited. Important information is lost, however, when the fluctuations in drag are ignored. This is particularly true when extreme drag forces are relevant; for instance, when predicting the survival of benthic animals on wave-swept shores and in torrential streams, or of plants in windblown terrestrial habitats.

This study reports on the probability distribution of drag fluctuations for five objects: a flat plate, large and small cylinders, a sphere and a limpet shell. Distributions vary substantially among different objects exposed to the same mainstream flow; the sphere and limpet exhibit larger fluctuations than the plate and cylinders. The distribution of extremes in drag is used to predict the likelihood that an organism will be dislodged. For organisms in which the applied fluid-dynamic stress is near the mean breaking stress (e.g. some corals, trees and mussels), calculations made using the extreme drag can yield a probability of dislodgment substantially higher than that calculated using the average.
Maintenance of Dynamic Strain Similarity and Environmental Stress Factor in Different Flow Habitats: Thallus Allometry and Material Properties of a Giant Kelp
Authors: Johnson A. S. , Koehl M. A. R.
Published: April 2021

We have focused on the giant kelp Nereocystis luetkeana to examine the mechanical scaling of benthic marine organisms loaded in tension by hydrodynamic forces. If we consider simply the allometry of the kelp’s morphological characters, we conclude that their stipes are underscaled relative to the blade area they support (i.e. that the kelp do not maintain stress or elastic similarity as they grow). However, a closer look at the characteristics of these kelp in the field reveals (1) that they have different blade shapes (and hence drag coefficients) and stipe material properties in different hydrodynamic environments, and (2) that they show a decrease in drag coefficient as they become larger. One consequence of these adjustments of blade and stipe morphology is that the maximum stresses in N. luetkeana stipes, when the kelp are pulled by peak tidal currents in their respective habitats, are similar for kelp of different sizes and for kelp from different sites. Hence, sessile organisms such as these kelp can, via their growth responses in different mechanical environments, show a phenomenon analogous to dynamic strain similarity. In addition, N. luetkeana also maintain a constant environmental stress factor, the ratio of the stress required to break a component of an organism (in this case the stipe) at some stage in its life to the maximum stress normally encountered in the habitat by that component during that stage (in this case, stress due to the drag on a kelp exposed to the peak tidal currents typical of the site at which it lives), both between habitats and as they grow.
Renal and Small Intestinal Sodium-Dependent Symporters of Phosphate and Sulphate
Authors: Murer Heini , Markovich Daniel , Biber Jürg
Published: April 2021

Homeostasis of inorganic phosphate (Pi) and sulphate (Si) is largely achieved by absorption in the mammalian small intestine and by reabsorption in the proximal tubule of the kidney. Under normal physiological conditions, the kidney appears to play the major role in maintaining the extracellular concentration of these anions. In both epithelia, reabsorption of Pi and to some extent also of Si underlie a variety of regulatory acute and chronic control mechanisms. Acute regulatory mechanisms are predominantly found in renal Pi reabsorption, whereas chronic regulation of transepithelial Pi transport is observed in both tissues. Also, in both epithelia, apically located sodium-dependent transport systems (Na+/Pi and Na+/Si symport) represent major targets for known regulatory factors.

By expression cloning using oocytes of Xenopus laevis, renal and small intestinal Na+-dependent phosphate and sulphate transport systems have been identified. Evidence has been obtained that cloned Na+/Pi and Na+/Si symporters are localized in the apical membrane of proximal tubular or small intestinal epithelial cells respectively. Furthermore, recent results indicate that one of the cloned Na+/Pi symporters is involved in the physiological and pathophysiological regulation of proximal tubular Pi reabsorption.