bluuebunny/crossref_metadata_2025 huggingface dataset:
The Effects of Seasonal Variations in Temperature on Extracellular Acid–Base Status in a Wild Population of the Crayfish Austropotamobius Pallipes
Authors: Whiteley N. M. , Taylor E. W.
Published: April 2021

Between February 1990 and February 1991, a wild population of Austropotamobius pallipes (L.) inhabiting a large, shallow, freshwater pool in Staffordshire, central England, experienced environmental fluctuations in water temperature (1–21°C) and pH (8.2–9.5). Moulting was seasonal, with crayfish entering pre- and postmoult between May and August. Haemolymph pHa levels declined in the spring when temperatures increased from 8 to 18°C (ΔpH/Δt=−0.013pHunits°C−1). This decrease was accompanied by a fall in [HCO3− ] (of 4.12mmol l−1) and [lactate] (of 4.71mmol l−1) and a premoult elevation in to 0.59kPa. After ecdysis, when water temperatures and pH were at their maxima, pHa levels increased, they continued to increase as temperature fell in late summer, reaching 7.97 in intermoult crayfish at 13°C during September. This increase was accompanied by a decrease in to 0.22kPa at constant [HCO3−1] (5–6mmol l−1). Between September (13°C) and October (11°C) pHa fell to 7.87 with an elevation in (of 0.18kPa) and [lactate] (of 1.84mmol l−1). As temperature continued to decrease (11–1°C), pHa remained unchanged despite an elevation in [HCO3− ] by 2.4mmol l−1 at constant . A mechanism accounting for the unvarying haemolymph pH values at low temperatures is proposed, stressing the importance of temperature-related seasonal changes in CO2 solubility and measured values for pK1′ in addition to adjustments in [HCO3−] and . These were apparently unaffected by changes in collecting and holding protocols.
The Energetics of Locomotion and Load Carriage in the Desert Harvester ant Pogonomyrmex Rugosus
Authors: Lighton John R. B. , Weier Jonathon A. , Feener Donald H.
Published: April 2021

The locomotion and load carriage energetics of the southwestern American harvester ant, Pogonomyrmex rugosus, were quantified at several temperatures within their normal foraging temperature range using a voluntary locomotion regime (‘running tube respirometer’). In a metabolic rate (MR) versus running speed regression, the intercepts for the individual ants differed significantly, so data were evaluated using analysis of covariance (ANCOVA) rather than the more common pooling of individuals. Unladen cost of transport was 158 J kg−1 m−1. The mean y-axis intercept did not differ significantly from zero after temperature-corrected standard MR (SMR) had been subtracted from MR; i.e. the y-axis intercept was not elevated above SMR. When the data were pooled, standard tests of the cost of load carriage showed that the costs of load and body carriage were statistically equivalent. However, using ANCOVA to regress MR-SMR against the product of running speed and load ratio showed that the cost of load carriage in P. rugosus is approximately 40% lower per unit mass than is the cost of body mass carriage (load ratio range 1.06–2.27). General methods are developed and described for evaluating and predicting locomotion and load carriage costs in small insects using data spanning a variety of temperatures and load ratios.
Crayfish Skeletal Muscle Requires Both Influx of External Ca2+ and Ca2+ Release from Internal Stores for Contraction
Authors: Ushio Hideki , Watabe Shugo , Iino Masamitsu
Published: April 2021

The isometric tension and membrane potential of single skeletal muscle fibres from the flexor muscle of the carpopodite in the meropodite of crayfish Procambarus clarkii (Girard) were studied to determine whether crayfish muscle contraction requires Ca2+ release from the sarcoplasmic reticulum. Contraction elicited by brief extracellular electrical stimulation was reduced by the removal of Ca2+ or by the addition of 25 μmol l−1 nicardipine in crayfish Ringer’s solution. Addition of 30 μmol l−1 ryanodine with 1mmol l−1 caffeine induced a transient contracture, the peak tension of which was 10–30% of that of the high-K+induced contracture and which declined to the pretreatment level in 20–60min. After ryanodine–caffeine treatment, 30mmol l−1 caffeine failed to induce contraction, suggesting that intracellular Ca2+ stores had been exhausted by the treatment. Extracellular electrical stimulation also failed to induce contraction after ryanodine–caffeine treatment, although the resting potential was not changed. These results suggest that Ca2+release from the sarcoplasmic reticulum, together with Ca2+ influx via nicardipine-sensitive Ca2+ channels, is essential to the contraction of crayfish leg muscle fibres after a brief membrane depolarization.
Geomagnetic Orientation of Loggerhead Sea Turtles: Evidence for an Inclination Compass
Authors: Light Phillip , Salmon Michael , Lohmann Kenneth J.
Published: April 2021

Recent experiments have demonstrated that hatchling loggerhead sea turtles can orient using the earth’s magnetic field. To investigate the functional characteristics of the loggerhead magnetic compass, we tested the orientation of hatchlings tethered inside a circular arena surrounded by a coil system that could be used to reverse the vertical and horizontal components of the ambient field. Hatchlings tested in darkness in the earth’s magnetic field were significantly oriented in an eastward direction. Inverting the vertical magnetic field component resulted in an approximate reversal of orientation direction, whereas reversing both the vertical and horizontal components together did not. The hatchlings failed to orient in a horizontal field of earth-strength intensity. These results provide evidence that the magnetic compass of loggerheads is an inclination (axial) compass, functionally similar to that of birds.
The Active Control of Wing Rotation by Drosophila
Authors: Dickinson Michael H. , Lehmann Fritz-Olaf , Götz Karl G.
Published: April 2021

This paper investigates the temporal control of a fast wing rotation in flies, the ventral flip, which occurs during the transition from downstroke to upstroke. Tethered flying Drosophila actively modulate the timing of these rapid supinations during yaw responses evoked by an oscillating visual stimulus. The time difference between the two wings is controlled such that the wing on the outside of a fictive turn rotates in advance of its contralateral partner. This modulation of ventral-flip timing between the two wings is strongly coupled with changes in wing-stroke amplitude. Typically, an increase in the stroke amplitude of one wing is correlated with an advance in the timing of the ventral flip of the same wing. However, flies do display a limited ability to control these two behaviors independently, as shown by flight records in which the correlation between ventral-flip timing and stroke amplitude transiently reverses. The control of ventral-flip timing may be part of an unsteady aerodynamic mechanism that enables the fly to alter the magnitude and direction of flight forces during turning maneuvers.
The Cost of Hovering and Forward Flight in a Nectar-Feeding Bat, Glossophaga Soricina, Estimated From Aerodynamic Theory
Authors: Norberg Ulla M. , Kunz Thomas H. , Steffensen John Fleng , Winter York , Helversen Otto Von
Published: April 2021

Energy expenditure during flight in animals can best be understood and quantified when both theoretical and empirical approaches are used concurrently. This paper examines one of four methods that we have used to estimate the cost of flight in a neotropical nectar-feeding bat Glossophaga soricina (Phyllostomidae), namely the use of kinematic and morphological data and aerodynamic theory to estimate the mechanical power requirements (power output) for hovering and horizontal forward flight. A hot-wire anemometer was used to measure induced velocity (the velocity of air accelerated by the wings) during hovering in order to estimate induced power. Our estimate of aerodynamic power (the sum of induced, profile and parasite powers) required for a 0.0105 kg G. soricina to hover is 0.15W and our estimate of the inertial power (the power required to oscillate the wings) is 0.19W. Thus, the total mechanical power for hovering is 0.34W or 32.4 W kg−1. The mechanical power required for horizontal forward flight, near the minimum power flight speed (4.2ms−1) for a 0.0117kg bat is 0.14W (12.3W kg−1), of which 0.10W is aerodynamic power and 0.042W is inertial power. Comparison with our results on metabolic power requirements estimated from nectar intake gives a mechanical efficiency of 0.15 for hovering flight and of 0.11 for forward flight near the minimum power speed.
The Locust Tegula: Significance for Flight Rhythm Generation, Wing Movement Control and Aerodynamic Force Production
Authors: Wolf Harald
Published: April 2021

The tegula, a complex sense organ associated with the wing base of the locust, plays an important role in the generation of the flight motor pattern. Here its function in the control of wing movement and aerodynamic force production is described.

The vertical component of forewing movement was monitored while recording intracellularly from flight motoneurones during stationary flight. First, in accordance with previous electrophysiological results, stimulation of hindwing tegula afferents was found to reset the wingstroke to the elevation phase in a well-coordinated manner. Second, recordings made before and after removal of fore-and hindwing tegulae were compared. This comparison demonstrated that the delayed onset of elevator motoneurone activity caused by tegula removal is accompanied by a corresponding delay in the upstroke movement of the wings.

The consequences of this delayed upstroke for aerodynamic force production were investigated by monitoring wing movements and lift generation simultaneously. A marked decrease in net lift generation was observed following tegula removal. Recordings of wing pronation indicate that this decrease in lift is primarily due to the delayed upstroke movement – that is, to a delay of the wings near the aerodynamically unfavourable downstroke position.

It is concluded that the tegula of the locust hindwing signals to the nervous system the impending completion of the wing downstroke and allows initiation of the upstroke movement immediately after the wings have reached the lower reversal point of the wingstroke. The functional significance of tegula feedback and central rhythm generation for locust flight control are discussed.
Actions Of Vesamicol On An α-Bungarotoxin-Sensitive Neuronal Nicotinic Acetylcholine Receptor
Authors: Buckingham S. D. , Lummis S. C. R. , Balk M. L. , Schroeder M. , Sattelle D. B.
Published: April 2021

Electrophysiology and binding studies were used to determine the actions of vesamicol [2-(4-phenylpiperidino)cyclohexanol, (AH5183)] on an α-bungarotoxin-sensitive, neuronal nicotinic acetylcholine receptor in the nervous system of the cockroach, Periplaneta americana. Electrophysiological studies on an identified motor neurone revealed a reversible blocking action of (±)-vesamicol on the response to ionophoretically applied acetylcholine with an IC50 value of 8.0×10−6 mol l−1. The block was weakly voltage-dependent over the membrane potential range of −50mV to −90mV, and appeared to be non-competitive. No difference in potency was observed between the resolved stereoisomers. (±)-Vesamicol was found to suppress specific binding of 125I-labelled αbungarotoxin to cockroach nervous tissue with an IC50 value of 5.1×10−3 mol l−1 and an estimated Hill coefficient of 0.73. Differences in the Hill coefficients were found when the resolved stereoisomers were tested separately. These data provide the first demonstration of a blocking action by vesamicol of a neuronal nicotinic acetylcholine receptor.
Glibenclamide Binding in Vertebrate Cardiac Membranes
Authors: Mckean Thomas A. , Rocklage Ann , Schneider Rudy J.
Published: April 2021

ATP-sensitive potassium channels (KATP) were discovered by Noma (1983) in the cardiac myocyte. These channels are modulated by intracellular ATP concentration. They are usually open and leak potassium under conditions when cellular energy demand exceeds energy supply, for example during hypoxia or ischemia. They are also found in the central nervous system, smooth muscle and pancreas (Ashcroft, 1988). Their role in the control of insulin secretion has been well established (Petersen, 1990). Recent studies have shown that KATP channels are important in protecting the heart during ischemia (Grover et al. 1989; Gross and Auchampach, 1992) and during hypoxia (McKean and Branz, 1992). These channels have also been implicated in the phenomenon of preconditioning (Auchampach et al. 1992). The mechanism for cardiac protection has not been well established; however, KATP opening shortens the cardiac action potential and may limit calcium entry and reduce the metabolic demand of the myocyte (Cole et al. 1991). The channel opening is responsible for an initial extracellular accumulation of potassium that may also serve to decrease metabolic demand on the heart (Wilde et al. 1990). The open channels, however, could be detrimental to the heart during reperfusion or reoxygenation as they would facilitate re-entry phenomena and arrhythmias (Wolleben et al. 1989). Studies from this laboratory have shown that the heart of the semi-aquatic diving rodent, the muskrat (Ondatra zibethicus), is able to survive ischemia and hypoxia better than the heart of a similarly sized non-diving rodent, the guinea pig (McKean and Landon, 1982; McKean, 1984). We hypothesized that the KATP channel might be involved in the explanation for this species difference.
Segment-Specific Modulation of the Electrophysiological Activity of Leech Retzius Neurons by Acetylcholine
Authors: Szczupak Lidia , Jordan Sheryl , Kristan William B.
Published: April 2021

The acetylcholine responses of Retzius neurons were electrophysiologically and pharmacologically characterized in situ and in culture. Single-electrode voltage-clamp was used to record currents from leech Retzius neurons from standard segments [Rz(X)] and from reproductive segments [Rz(5,6)]. A 1s pressure pulse of acetylcholine (ACh) produced a fast inward current followed by a slower outward current in Rz(X) neurons, whereas it produced only an outward current in Rz(5,6) neurons. These segment-specific responses were maintained when the two types of Retzius neurons were isolated in culture for up to 12 days. The inward current of Rz(X) reversed at around –25mV and was partially carried by Na+. This cationic current desensitized rapidly. The outward current of Rz(X) and Rz(5,6) neurons reversed at around –65mV and was carried by Cl−. This anionic current desensitized very slowly upon prolonged applications of ACh. The expression of the ACh-induced outward current in Rz(X) was season-dependent and was recorded in a larger proportion of Rz(X) neurons during the summer than during the winter. The expression of the ACh-induced outward current in Rz(5,6) did not show any seasonal pattern. The fast inward current of Rz(X) was also elicited by nicotine; it was blocked by d-tubocurarine, hexamethonium and mecamylamine, but was not affected by α-bungarotoxin. The outward current of Rz(X) and Rz(5,6) was also elicited by nicotine and by 4-[N-(3-chlorophenyl)carbamoxyloxy]2-butynyltrimethylammonium chloride (a muscarinic agonist); it was blocked by d-tubocurarine and by α-bungarotoxin, but it was not affected by hexamethonium or mecamylamine. The results show that the serotonergic Retzius neurons of the leech could be tonically inhibited by ACh. In addition, the Retzius neurons from standard segments could also be phasically excited by ACh. The receptors responsible for the excitation fit into the classification of neuronal nicotinic receptors, whereas the receptors mediating the inhibition are closer in type to the muscular nicotinic receptor.
Performance of a Butterfly in Take-Off Flight
Authors: Sunada Shigeru , Kawachi Keiji , Watanabe Isao , Azuma Akira
Published: April 2021

The flight of a butterfly, Pieris melete, was observed in the take-off phase and was analyzed theoretically from aerodynamic and kinetic viewpoints. A vortex method, which was recently developed by the present authors, was used in this analysis.

During the downstroke, the butterfly generates mainly a vertical force. The acceleration of the butterfly’s body during the first half of the downstroke is especially large, and this acceleration is mainly caused by a large unsteady pressure drag acting on the wings. This large unsteady pressure drag is generated by the vortices shed into the flow from the outer edges of each wing of a pair; it is increased by the interference effect between a pair of wings when the opening angle is small. This force can be estimated by the previous quasi-steady analysis when the force coefficient is changed to 4. In addition to the unsteady pressure drag, an aerodynamic force due to added mass is generated and this is also increased by the interference effect between a pair of wings.

During the upstroke the butterfly generates mainly a horizontal force. The change of direction of the forces during the down- and upstrokes is controlled by variation in the inclination of the stroke plane. The moment, which is created by the aerodynamic force acting on the wings and by abdominal motion, changes the thoracic angle, that is the inclination of the stroke plane.
Collision Avoidance of Flying Locusts: Steering Torques and Behaviour
Authors: Robertson R. Meldrum , Johnson Amanda G.
Published: April 2021

Obstacles approaching in the flight path trigger postural and wing kinematic adjustments in tethered flying locusts. We sought to confirm that these behaviours were steering behaviours by measuring the changes in the flight forces associated with their execution. We also investigated the coordination of these behaviours in the execution of collision avoidance manoeuvres and the effect of speed or size of the obstacle on the timing and magnitude of the response. Locusts were tethered and suspended in a wind tunnel from orthogonally arranged leaf springs mounted with strain gauges. Lift and yaw torque could be monitored unambiguously. We also monitored a forward translation force which combined pitch and thrust. During flight, the locusts were videotaped from behind while targets of different sizes (5cm×5 cm, 7cm×7 cm, 9cm×9cm, 11cm×11cm) were transported towards the head at different speeds (1, 2, 3 or 4 ms−). Angular asymmetry of the forewings during the downstroke with the right forewing high, and abdomen and hindleg movement to the left, were temporally associated with an increase in yaw torque to the left. With the left forewing high, abdomen and hindleg movement to the right were temporally associated with a decrease in yaw torque to the left. Obstacle avoidance behaviours could be associated with either an increase or a decrease in the pitch/thrust component. Leg, abdomen and wingbeat alterations in response to the approach of an obstacle were independent but tightly coordinated. Slower approaches increased the magnitude of the responses. However, the size of the obstacle had no effect on the magnitude of the response. Slower and larger targets generated earlier reactions (i.e. locusts reacted when the targets were further from the head). We conclude that the behaviours we have described were steering behaviours which would have directed the animal around an obstacle in its flight path, and that there were at least two strategies for collision avoidance associated with slowing or speeding flight. Leg, abdomen and wingbeat alterations formed a coherent avoidance response, the magnitude of which was dependent upon the time available for it to develop. We further conclude that the manoeuvre was not initiated at a constant time to collision and we propose that the avoidance strategy was to initiate the manoeuvre when the targets subtended more than 10° in the insect’s field of view.
Transepithelial Movement of Calcium in Crustaceans
Authors: Neufeld Douglas S. , Cameron James N.
Published: April 2021

The regulation of calcium in most crustaceans is especially challenging owing to the highly mineralized cuticle that must be recalcified after each moult, a process that often occurs in environments with low concentrations of calcium. The gill and carapace epithelia separate the major calcium-containing compartments of the body and therefore see large changes in the rate of calcium flux through the moult cycle. Large changes in the ultrastructure of these cells do not, however, correlate well with the periods of calcium movement and probably reflect other physiological events. Despite the challenges to regulating calcium levels at various acclimation salinities and moult stages, the calcium concentration in the blood is maintained relatively constant. There is a rapid increase to a high rate of calcium flux across both the gill and carapace epithelium shortly after the moult; on an area-specific basis these fluxes are among the highest reported for calcium-transporting epithelia. When in water with a very low concentration of calcium, the electrochemical gradient for calcium is directed outwards and net influx must occur by active transport. Evidence suggests that changes in the electrochemical gradient, permeability and active transport are all important in the ability of crustaceans to take up calcium from water with a low concentration of this ion. Although an enzyme transporter is presumably involved in the active transport of calcium across epithelia, very little is known about the cellular mechanism of the transepithelial movement of calcium in crustaceans.
Spatial Aspects of Ca2+Signalling in Pancreatic Acinar Cells
Authors: Thorn Peter
Published: April 2021

Secretory cells do not only respond to an agonist with a simple rise in [Ca2+]i. It is now clear that complex patterns of [Ca2+]i elevation in terms of space and time are observed in many cell types and that these patterns may be a cellular mechanism for the regulation of different responses. Ca2+ signalling in exocrine cells of the pancreas promotes the secretion of digestive enzymes and fluid. It has been shown that at high concentrations of agonist (acetylcholine or cholecystokinin) the [Ca2+]i response is initiated in the secretory pole of the cell before spreading across the whole cell. This site of initiation of the [Ca2+]i elevation is in the region where exocytotic release of enzymes occurs and is also the site of a Ca2+-dependent chloride channel thought to be crucially important for fluid secretion. Lower concentrations of agonist elicit [Ca2+]i oscillations with complex repetitive patterns characteristic of each agonist. At physiological agonist concentrations, we have recently described repetitive short-lasting Ca2+ spikes that are spatially restricted to the secretory pole of the cell. In addition to these spikes, cholecystokinin also promotes slow transient Ca2+ rises that result in a global rise in Ca2+. The inositol trisphosphate (InsP3) receptor plays a crucial role in all of these various agonist responses, most of which can be reproduced by the infusion of InsP3 into the cell. The high InsP3-sensitivity of the secretory pole is postulated to be due to a localization of high-affinity InsP3 receptors. We speculate that in response to cholecystokinin the short-lasting spikes elicit exocytosis from a small ‘available pool’ of vesicles and that the broader oscillations induce both exocytosis and cell changes that involve movement of vesicles into this ‘available pool’.
Modulation of Signalling Initiated by Phosphoinositidase-C-Linked Receptors
Authors: H. Wojcikiewicz Richard J. , Nahorski Stefan R.
Published: April 2021

An extensive group of cell surface receptors are coupled to phosphoinositidase C and thus to the production of the intracellular second messengers inositol 1,4,5-trisphosphate and 1,2-diacylglycerol. While the mechanisms and consequences of phosphoinositidase C activation have been the target of intensive study for over a decade, information is scarce regarding the regulatory processes that modulate this system during receptor stimulation. This situation, however, is now beginning to change. Recent data indicate (a) that Ca2+, mobilized concurrently with activation of phosphoinositidase-C-linked receptors, is a feedback activator and amplifier of phosphoinositide hydrolysis, (b) that rapid desensitization, possibly associated with receptor phosphorylation, regulates phosphoinositidase-C-linked receptors, (c) that receptor internalization can mediate desensitization at later times and (d) that signalling can be regulated at additional sites downstream of phosphoinositidase C. These diverse regulatory events provide the means by which the breakdown of phosphoinositides and cellular responsiveness to their products are controlled during cell stimulation.
Regulation of Inositol 1,4,5-Trisphosphate Receptors
Authors: Marshall Ian C. B. , Taylor Colin W.
Published: April 2021

Inositol 1,4,5-trisphosphate [Ins(1,4,5)P3] is a soluble second messenger responsible for the generation of highly organized Ca2+ signals in a variety of cell types. These Ca2+ signals control many cellular responses, including cell growth, fertilization, smooth muscle contraction and secretion. Ins(1,4,5)P3 is produced at the plasma membrane following receptor activation, but rapidly diffuses into the cytosol, where it binds to specific receptors through which it mobilizes intracellular Ca2+ stores. The actions of Ins(1,4,5)P3 within cells are tightly controlled: enzymes control the rapid generation and metabolism of Ins(1,4,5)P3 following receptor activation; multiple Ins(1,4,5)P3 receptor subtypes and splice variants exist, some of which are differentially expressed between cell types and at different stages of development; and Ins(1,4,5)P3 receptors are the targets for a number of allosteric regulators, including protein kinases, ATP and divalent cations. Understanding how cells control the Ca2+-mobilizing activity of Ins(1,4,5)P3 will be important if we are to unravel the mechanisms that underlie the complex arrangements of Ca2+ signals.
The Role of Ca2+ in Signal Transduction Following Fertilization in Fucus Serratus
Authors: Roberts S. K. , Berger F. , Brownlee C.
Published: April 2021

The marine brown alga Fucus serratus represents one of the few multicellular plant species in which the process of fertilization can be studied relatively easily. Fertilization marks the onset of a cascade of events associated with egg activation. Fertilization in Fucus serratus bears several superficial similarities to fertilization in several animal systems. The essential features of Fucus serratus egg activation are compared with those of protostome and deuterostome animal systems. Ca2+ is required for egg activation in Fucus serratus and cytosolic [Ca2+] changes can be observed in fertilizing eggs. However, these are small and variable in comparison with those occurring in deuterostomes, and fertilization can proceed normally in the absence of any global cytosolic Ca2+ transients. A model for egg activation in Fucus serratus is presented, invoking a role for both Ca2+ influx and localized propagation of the sperm signal around the plasma membrane by an as yet unidentified mechanism. Polarity in Fucus serratus is acquired a considerable time after fertilization and the role of cytosolic Ca2+ gradients in the acquisition and expression of polarity is discussed. The problem of the signals associated with the onset of the cell cycle in the fertilized Fucus serratus egg is also addressed.
Medullary Bone and Avian Calcium Regulation
Authors: Dacke C. G. , Arkle S. , Cook D. J. , Wormstone I. M. , Jones S. , Zaidi M. , Bascal Z. A.
Published: April 2021

Medullary bone forms in egg-laying birds in response to gonadal steroids and is the most overtly oestrogen-dependent of all bone types. It acts as a labile reservoir for the supply of eggshell calcium. Previous studies indicate that feeding calcium- and vitamin-D-deficient diets to chickens results in resorption of cortical rather than medullary bone. More recent studies in calcium-stressed quail hens question this hypothesis and suggest that during the first 2 weeks of dietary calcium depletion the medullary bone is resorbed while cortical bone volume remains intact. The role of the osteoclast in bone resorption is the focus of much research that has recently included studies of medullary bone osteoclasts. The functional morphology of the avian cells, i.e. changes from quiescent to active osteoclasts with ruffled borders, reflects the rapid changes in medullary bone turnover that occur during the egg-laying cycle. Unlike mammalian osteoclasts, those from avian sources generally appear refractory to inhibitory factors such as calcitonin or raised extracellular calciumconcentration. However, medullary bone osteoclasts cultured in vitro for several days recover their ability to respond to the latter factor by increasing their levels of free cytosolic Ca2+, reducing tartrate-resistant acid phosphatase secretion and reducing their cell spread area. It is suggested that factors such as ambient calcium levels and prostaglandins may form part of a system of rapid local control for medullary bone osteoclast activity.
Calcium Handling by the Mammalian Kidney
Authors: Bindels R. J. M.
Published: April 2021

The mammalian kidney plays a crucial role in the Ca2+ homeostasis of the body. To maintain a net Ca2+ balance, more than 98% of the filtered load of Ca2+ must be reabsorbed along the nephron. There are two potential pathways through which net Ca2+ reabsorption can occur. First, a paracellular and passive route that predominates in the proximal tubules and thick ascending limb of Henle’s loop. Second, a transcellular, active transport that characterises Ca2+ reabsorption in the distal nephron. Transcellular Ca2+ transport involves passive influx across the luminal membrane, diffusion through the cytosol and active extrusion across the peritubular membrane. The rate of active Ca2+ reabsorption is controlled by the calciotropic hormones, i.e. parathyroid hormone, calcitonin and 1,25-dihydroxyvitamin D3. The application of new techniques in renal physiology has greatly increased our knowledge of the renal handling of Ca2+ and allowed the examination of Ca2+ transport processes at the cellular and subcellular level. This review focuses primarily on the mechanisms and regulation of transcellular Ca2+ transport. The distal nephron consists of at least four discrete segments and the contribution of each segment to active transcellular Ca2+ is discussed in detail.
Kinetic and Structural Adaptations of Cytoplasmic Malate Dehydrogenases of Eastern Pacific Abalone (Genus Haliotis) From Different Thermal Habitats: Biochemical Correlates of Biogeographical Patterning
Authors: Dahlhoff Elizabeth , Somero George N.
Published: April 2021

We measured the effects of temperature on cytosolic malate dehydrogenases (cMDHs) from the shell muscle of five species of eastern Pacific abalone, genus Haliotis, found at different latitudes and/or tidal heights. The apparent Michaelis–Menten constant (Km) of coenzyme (nicotinamide adenine dinucleotide, NADH) was conserved within a narrow range (11–21 μmol l−1) at physiological temperatures for all species. However, elevated temperatures perturbed the Km of NADH for cMDHs of the two species living at higher latitudes and/or lower tidal heights [Haliotis rufesens (red) and H. kamtschatkana kamtschatkana (pinto)] to a much greater extent than for cMDHs of congeners from lower latitudes and/or higher tidal heights [H. fulgens (green), H. corregata (pink) and H. cracherodii (black)]. The apparent Arrhenius activation energies for the cMDHs of these five species showed a similar interspecific divergence. Furthermore, green, pink and black abalone have cMDHs that are more resistant to thermal denaturation than are cMDHs of red and pinto abalone. Native gel electrophoresis showed that cMDHs of red and pinto abalone had identical mobilities, whereas cMDHs of green, pink and black abalone are distinct both from each other and from that of the two cold-adapted species. These data suggest that cMDHs from the abalone species living in warm habitats are adapted to function optimally at higher temperatures than are the cMDHs of the two species living in cooler habitats. The relationships suggested by these criteria are in agreement with other studies that used morphological and molecular indices to predict abalone phylogeny. These results therefore provide further evidence that interspecific variation in protein structure and function may be driven by natural selection based on only small (i.e. several degrees Celsius) differences in average body temperature, and that such selection is an important element of the mechanisms of species formation and the maintenance of biogeographic patterning.
Skeletal Strain Patterns in Relation to Exercise Training During Growth
Authors: Biewener Andrew A. , Bertram John E. A.
Published: April 2021

Bones are believed to alter their shape in response to changes in tissue strains produced by physical activity and the goal of this study is to examine whether modeling responses of a growing bone to changes in physical exercise are adjusted to maintain a uniform distribution of functional strains. We test this idea by comparing in vivo strains recorded in the tibiotarsus of white leghorn chicks during ‘intensive’ treadmill exercise (60% of maximum speed, carrying a weight equal to 20% body weight on the trunk: 60%/L) with strains that had been recorded previously during ‘moderate’ treadmill exercise (35% of maximum speed, unloaded: 35%/UNL) at similar bone sites. Our hypothesis is that modeling adjustments of bones subjected to the intensive load-carrying exercise should re-establish strains recorded in the bones subjected to moderate exercise. At each exercise level, the animals were exercised for 5 days per week (2500 loading cycles per day) from 2 to 12 weeks of age. As in the moderate exercise group studied earlier, strains measured at six functionally equivalent sites on the tibiotarsus of the 60%/L group were consistently maintained during growth from 4 to 12 weeks of age. In addition, the pattern of strain recorded at these sites was uniformly maintained over the full range of speeds recorded (from 0.48 to 2.70 ms−1 at 12 weeks of age). Peak strains measured at 4 weeks of age in the load-carrying exercise group were initially elevated by 57% overall compared with peak strains recorded in the moderate exercise group. At 8 weeks of age, strain levels in the 60%/L group differed by only 4% overall compared with those recorded in the 35%/UNL group. The nature of strain (tensile versus compressive) and the orientation of principal strain at corresponding sites were also similar in the two groups. At 12 weeks of age, however, bone strain levels in the 60%/L group were again elevated (47% overall) compared with those recorded in the 35%/UNL group, although the general pattern and orientation of strains remained similar. This finding suggests a transient modeling response of the bone to the onset of exercise training, which was lost during subsequent growth, possibly because the normal pattern of functional strain was not altered significantly by the faster load-carrying exercise.
Functional and Molecular characteristics of a primitive vertebrate glucose transporter: studies of glucose transport by erythrocytes from the pacific hagfish (Eptatretus Stouti)
Authors: Young J. D. , Yao S. Y.-M. , Tse C. M. , Davies A. , Baldwin S. A.
Published: April 2021

The characteristics of glucose transport were investigated in erythrocytes of a primitive vertebrate, the Pacific hagfish (Eptatretus stouti) Lockington. Transport of glucose by intact hagfish erythrocytes and by phospholipid vesicles reconstituted with n-octylglucoside extract of hagfish erythrocyte membranes was rapid and mediated by a saturable stereospecific mechanism sensitive to inhibition by cytochalasin B. Covalent photoaffinity labelling experiments with [3H]cytochalasin B identified the hagfish glucose transporter on SDS/polyacrylamide gels as a protein with an apparent average Mr of 55 000. Amino acid sequence homology between the hagfish and human erythrocyte glucose transporters (GLUT 1) was investigated in immunoblotting experiments using a panel of 12 different antipeptide antisera and affinity-purified antibodies raised against cytoplasmic extramembranous regions of the human transporter, and with an antibody to the intact purified human protein. The latter antibody labelled a component in the membrane with the same apparent Mr as cytochalasin B. Two affinity-purified antipeptide antibodies, corresponding to residues 240–255 and 450–467 of the human erythrocyte transporter, also labelled a component in the membrane with this relative molecular mass, demonstrating localised sequence similarity between the polypeptides of the two species within the central cytoplasmic loop and within the cytoplasmic C-terminal region. Glucose transport by hagfish erythrocytes was not coupled to the movement of protons.
Actions of bicuculline on cell body and neuropilar membranes of identified insect neurones
Authors: Buckingham S. D. , Hue B. , Sattelle D. B.
Published: April 2021

Bicuculline and its methochloride salt block inhibitory postsynaptic potentials recorded from giant interneurone 2 (GI 2) of the cockroach Periplaneta americana following stimulation of cercal nerve X, but fail to block the response to -y-aminobutyric acid (GABA) when this neurotransmitter is ionophoresed or pressure-injected onto the fine branches of GI 2 within the neuropile of the terminal abdominal ganglion. Bicuculline is similarly ineffective in blocking the response recorded when GABA is ionophoresed onto the cell body membrane of GI 2.

The cell body membranes of cockroach GI 2 and fast coxal depressor motor neurones have been used to show that bicuculline blocks cell body (extrasynaptic) neuronal nicotinic acetylcholine receptors. Pressure-injection of acetylcholine into the neuropile results in a depolarization of GI 2 that is blocked by bicuculline. Therefore, the block by bicuculline of inhibitory postsynaptic potentials recorded from GI 2 may result in part from actions at sites other than synaptic GABA receptors. Alternatively, there may exist a population of synaptic GABA receptors on GI 2 that, unlike GI 2 cell body GABA receptors, are sensitive to bicuculline.
The intrinsic properties of an in situ perfused crocodile heart
Authors: Franklin C. E. , Axelsson M.
Published: April 2021

An in situ perfused crocodile (Crocodylus porosus) heart preparation was developed to investigate the effects of input and output pressure on cardiac dynamics and to determine the conditions that lead to a right-to-left cardiac shunt. The pericardium was kept intact, both the left and right atria were perfused and all three outflow tracts (right aortic, left aortic and pulmonary) were cannulated, enabling pressures and flows to be monitored. The perfused heart preparation had an intrinsic heart rate of 34 beats min-1 and generated a physiological power output.

Both the left and right sides of the heart were sensitive to filling pressure. Increasing the filling pressure to both atria resulted in an increase in stroke volume and cardiac output (Frank–Starling effect). Increasing the filling pressure to the right atrium also had a positive chronotropic effect. Large right ventricular stroke volumes initiated a right-to-left shunt, despite the left aorta having a pressure 1.5 kPa higher than the pulmonary output pressure.

The left ventricle was able to maintain its output and stroke volume up to an output pressure of approximately 8 kPa. However, the right ventricle was significantly weaker. Right ventricular output and stroke volume showed a marked decrease when the output pressure was increased above 5 kPa.

A right-to-left shunt occurred when pulmonary output pressure was increased. Surprisingly, a shunt occurred into the left aorta before the pressure in the pulmonary artery became greater than that in the left aorta. Once the pressure in the pulmonary artery exceeded the left aortic pressure, pulmonary artery flow ceased and right ventricular output was solely via the left aorta. A right-to-left shunt could also be initiated by increasing the filling pressure to the left atrium.
Cardiac output in conscious toads (Bufo marinus)
Authors: West Nigel H. , Smits Allan W.
Published: April 2021

Cardiac output and peripheral resistance have not been measured in conscious anuran amphibians, although some data exist for pithed and anaesthetized frogs (Shelton and Jones, 1965a,b; Shelton, 1970; Tazawa et al. 1979). The periodic lung ventilation characteristic of conscious anurans could increase cardiac output reflexively or by changes in venous return, as in mammals. Furthermore, because the undivided ventricle places the pulmonary and systemic vascular beds effectively in parallel, changes in the ratio of systemic to pulmocutaneous vascular resistance have the potential to alter the distribution of cardiac output. Therefore, the objectives of this study were to measure cardiac output and peripheral resistance in undisturbed, conscious Bufo marinus and to determine the effect of increased ventilation, stimulated by CO2, on pulmocutaneous blood flow and resistance.
Activation of a cation conductance by acetic acid in taste cells isolated from the bullfrog
Authors: Okada Y , Miyamoto T , Sato T
Published: April 2021

The ionic mechanism of the conductance activated by acetic acid was analyzed in isolated bullfrog taste cells under whole-cell voltage-clamp. Bath-application of acetic acid (pH 3.9–4.7) induced an inward current in about 80 % of the taste cells. The current occurred in external 80 mmol l−1 Ba2+ and internal 100 mmol l−1 Cs+, which completely blocked the delayed outward K+ current. The concentration–response relationship for the acid-activated current was consistent with that of the gustatory neural response. Prolonged adaptation of the surface of the tongue to HCl prior to taste cell isolation decreased the acid-induced current to about 20 % of the control value without decreasing NaCl-induced neural responses and voltage-activated Na+ currents. The results suggest that the transduction mechanism of the acid response might be different from that of the response to salt. The I–V relationship of the acid-induced response was nearly linear at membrane potentials between −80 and 80 mV. The acid-induced conductance was permeable to alkali metal and alkali earth metal ions. The permeability ratios were PCa:PBa:PSr:PNa:PCs=1.87:1.17:0.73:0.99:1.00. The present study suggests that the acid-induced receptor current in bullfrog taste cells is generated by an increase in a cation conductance in the apical taste membrane.
Correlation of sound generation and metabolic heat flux in the bumblebee Bombus lapidarius
Authors: Schultze-Motel Paul , Lamprecht Ingolf
Published: April 2021

Flying insects produce extreme amounts of heat as a by-product during the contractions of their thoracic flight muscles (Heinrich, 1989). Before flight, metabolic heat may serve to warm up the thoracic muscles until the minimum lift-off temperature is reached (Heinrich, 1974b; Stone and Willmer, 1989; Esch and Goller, 1991). Social bees and wasps are also able to use the heat produced in their flight muscles for brood incubation and for active regulation of nest temperatures (Heinrich, 1974a; Seeley and Heinrich, 1981; Schultze-Motel, 1991).
Effects of ammonia loading onPorcellio Scaber: Glutamine and glutamate synthesis, ammonia excretion and toxicity
Authors: Wright Jonathan C. , O’Donnell Michael J. , Reichert Johanna
Published: April 2021

The effects of ammonia loading in the terrestrial isopod Porcellio scaber were studied by exposing animals to atmospheres of high . Isopods show a remarkable tolerance of elevated ambient , with an LD50 of 89 Pa for a 7-day exposure. However, haemolymph total ammonia concentrations generally remained below 5 mmol l−1 (=0.37 Pa) over the range of ambient ammonia levels used (6.6–165 Pa). Following a 7-day loading period, whole-animal glutamine (Gln) and glutamate (Glu) levels increased in direct proportion to ambient , reaching values of 35 μmol g−1 fresh mass for glutamine and 12 μmol g−1 fresh mass for glutamate in 99 Pa ; these correspond to control levels of 7.5 μmol g−1 fresh mass and 5.9 μmol g−1 fresh mass, respectively. Following transfer to ammonia-free chambers, NH3 excretion rates were augmented five-to sixfold relative to non-loaded controls. Ammonia volatilization subsequently declined, approaching control levels after 8–9 days. Levels of Gln and Glu showed a concomitant decline to 13.7 μmol g−1 fresh mass and 9.2 μmol g−1 fresh mass, respectively. The results suggest that these amino acids function in ammonia sequestration and, hence, detoxification. Calculations indicate that mobilization of amino groups by deamination of accumulated Gln and Glu could explain 35 % of the increased ammonia production. Implications of NH3 volatilization for acid–base balance are discussed.
Somatostatin-related peptides isolated from the eel gut: effects on ion and water absorption across the intestine of the seawater eel
Authors: Uesaka Toshihiro , Yano Keiichi , Yamasaki Motoo , Nagashima Kei , Ando Masaaki
Published: April 2021

Four somatostatin-related peptides were isolated from eel guts. Two of them were the same as eel SS-25II (eSS-25II) and eel SS-25I (eSS-25I) isolated from European eel pancreas. The remaining two peptides were C-terminal tetradecapeptides (eSS-14II and eSS-14I) of eSS25II and eSS-25I, respectively. These four peptides all enhanced the serosa-negative transepithelial potential difference and short-circuit current across the seawater eel intestine after pretreatment with isobutylmethylxanthine, serotonin (5-HT) and methacholine, an agonist of acetylcholine (ACh). Among these peptides, eSS-25II was the most potent enhancer, followed by eSS-25I and eSS-14II. Since the large peptide (eSS-25II) acts at a lower concentration than the small somatostatin (eSS-14II), the 11 N-terminal amino acid residues seem to potentiate somatostatin action in the eel intestine. In contrast, eSS-14II was more potent than mammalian SS-14, indicating that the three amino acid residues (Tyr18, Gly21, Pro22) in the C-terminal portion also contribute to the potency of somatostatin. Endogenous somatostatin (eSS-25II) activated net Na+, Cl-and water fluxes across the seawater eel intestine. This stimulatory action was not inhibited by tetrodotoxin or yohimbine, an adrenergic antagonist, indicating that eSS-25II does not act through neuronal firing or through catecholamine release. Thus, eel somatostatins may act directly on the enterocytes, but on a distinct receptor from that for adrenaline, to antagonize the inhibition of NaCl and water absorption by 5-HT and ACh in the seawater eel intestine.