bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of Experimental Ventilation of the Skin On Cutaneous Gas Exchange in the Bullfrog
Authors: Burggren Warren W. , Feder Martin E. 
Published: April 2021

ABSTRACT
The significance of skin ventilation to cutaneous gas exchange in vertebrates has seldom been recognized. Unlike the lungs and gills, the skin lacks a dedicated ventilatory pump, and most analyses have implicitly or explicitly ignored skin ventilation because the skin is in contact with an ‘infinite pool’ (Piiper & Scheid, 1977) of respiratory medium. For example, models of gas exchangers consider amphibian skin to have an infinite ventilatory conductance (e.g. Piiper & Scheid, 1977) and in experimental studies the respiratory medium is often stirred thoroughly (e.g. Gottlieb & Jackson, 1976; Burggren & Moalli, 1984), which may eliminate any impact of ventilatory inadequacy upon cutaneous gas exchange. Indeed, as discussed by Piiper (1982) and Feder & Burggren (1985), most previous analyses have not accounted for ‘stratification’ or ‘diffusion boundary layers’ about the skin, which theoretically may limit cutaneous gas exchange, especially in still water. Skin ventilation may be important in dissipating such boundary layers, and several skinbreathing vertebrates have particular behaviour patterns that might serve this function (reviewed by Feder & Burggren, 1985). However, there is no direct experimental evidence that the movement of respiratory medium across the skin can affect cutaneous gas exchange.
Muscarinic Response In Rat Lacrimal Glands
Authors: Marty A. , Evans M. G. , Tan Y. P. , Trautmann A. 
Published: April 2021

ABSTRACT
A large variety of responses has been uncovered by recent investigations of conductance changes elicited by muscarinic agonists. In exocrine glands, the permeability to K+, Cl− and Na+ ions is increased, and internal Ca2+ serves as a second messenger. Patch-clamp analysis of the secreting cells has revealed three types of Ca2+-dependent channels, which are respectively selective for K+, for Cl−, and for monovalent cations. The channels differ in their sensitivity to the internal Ca2+ concentration, Ca,. K+-selective channels are partially activated at rest, with Ca, approx. 10 nmol I−1; Cl−-selective channels are activated between 100 nmol l−1 and 1 μmoll−1; activation of cationic channels requires micromolar Ca, levels.
Cell-attached recordings, performed either on isolated cells or on cell clusters, show an activation of all three channel types upon application of acetylcholine. In whole-cell recordings, mostly K+-and Cl−-selective channels are activated. The cell currents display slow oscillations linked to variations of Ca,. Whole-cell currents rise after a delay of approx. 1 s, and decay with a time constant of approx. 0·7 s upon removal of acetylcholine. They do not depend on extracellular Ca2+.
The recent demonstration that Ca2+-dependent currents can also be obtained when dialysing the cells with inositoltrisphosphate or with GTPγS, a non-hydrolysable analogue of guanosine triphosphate, opens promising leads to an analysis of intracellular events regulated by acetylcholine.
Allosteric Effects of Mg2+ on the Gating of Ca2+-Activated K+ Channels From Mammalian Skeletal Muscle
Authors: Golowasch Jorge , Kirkwood Alfred , Miller Christopher 
Published: April 2021

ABSTRACT
Ca2+-activated K+ channels from rat muscle transverse tubule membranes were inserted into planar phospholipid bilayers, and the activation of these channels by Ca2+ was studied. On the cytoplasmic side of the channel, calcium ions (in the range 10–100μmol l−1) increase the opening probability of the channel in a graded way. This ‘activation curve’ is sigmoid, with an average Hill coefficient of about 2. Magnesium ions, in the range 1–10 mmol l−1, increase the apparent affinity of the channel for Ca2+ and greatly enhance the sigmoidicity of the Ca2+ activation curve. In the presence of 10 mmol l−1 Mg2+, the Hill coefficient for Ca2+ activation is about 4·5. This effect depends upon Mg2+ concentration but not upon applied voltage. Mg2+ is effective only when added to the cytoplasmic side of the channel. The results argue that this high-conductance, Ca2+-activated K+ channel contains at least six Ca2+-binding sites involved in the activation process.
The Activity of the Horizontal Semicircular Canal of the Dogfish, Scyllium Canicula
Authors: Löwenstein Otto , Sand A. 
Published: April 2021

ABSTRACT
Oscillographic records from the horizontal ampulla of the dogfish show: (a) A spontaneous discharge of impulses when the fish is stationary in the normal position. (b) An increased discharge during ipsilateral rotation. (c) A diminution of the spontaneous discharge during contralateral rotation. (d) A prolonged after-discharge on stopping contralateral rotation. The threshold for the responses is an angular acceleration of the order of 11° per sec2. This mechanism provides a means of signalling to the centre equal and opposite phases of a biphasic physical change. The two opposite ampullae work antagonistically, and the reflex responses of the normal fish depend upon the balance of the afferent discharges from the left and right labyrinths.
Short Communication: Distribution of Ion Channels in the Membrane of the DinoflagellateNoctiluca Miliaris
Authors: Oami Kazunori , Naitoh Yutaka , Sibaoka Takao 
Published: April 2021

ABSTRACTNoctiluca miliaris, a marine dinoflagellate, exhibits spontaneous flexion of its tentacle. The movement of the tentacle is always accompanied by perturbations of membrane potential, termed the ‘tentacle regulating potentials’ (TRPs) (Eckert and Sibaoka, 1967). Though the waveform of the TRPs is liable to variation, it consists of four successive basic components: (1) a Na+-dependent depolarizing (positive) spike, (2) a depolarizing plateau potential, (3) a Cl−-dependent hyperpolarizing (negative) spike, and (4) a long-lasting hyperpolarization (Eckert and Sibaoka, 1967; Oami et al. 1988). A slow flexion of the tentacle is seen during the plateau, and the flexion is suddenly accelerated when the negative spike occurs. The tentacle then extends during the long-lasting hyperpolarization. There is no correlation between the positive spike and the tentacular movement (Hisada, 1957; Oami et al. 1988).
Muscle Recruitment During Terrestrial Locomotion: How Speed and Temperature Affect Fibre Type Use in a Lizard
Authors: Jayne Bruce C. , Bennett Albert F. , Lauder George V. 
Published: April 2021

ABSTRACT
Synchronized electromyography and cinematography were used to study the activity of the red and white regions of the iliofibularis muscle in savannah monitor lizards, Varanus exanthematicus (Bosc), during locomotion. Analysis of variance on results from four individuals moving at speeds of up to 1.5 km h−1 at two body temperatures (25 and 35 °C) revealed that all kinematic variables were significantly affected by speed but none was affected by temperature. Hence, patterns of limb movement at any speed were similar at both temperatures. However, this similarity resulted from differences in muscle activity. Analysis of variance on electromyographic variables for activity in the red and white regions showed widespread significant effects of both temperature and speed. The red region was active at all speeds, and it displayed regular bursts of activity which usually occurred when the foot was above the ground, the femur was being abducted and the knee flexed. Variables measuring the intensity of red region activity generally increased with speed until a maximum was attained and no further change occurred with additional increases in speed. The speed at which maximum red activity was attained at 25 °C was less than that at 35 °C. For equal locomotor speeds, amplitudes of electromyograms (EMGs) from the red region at 25 °C were greater than those at 35°C. In contrast to the red region, the white region was active only above some threshold speed, and activity was often rather irregular compared to that of the red region. At 25°C the threshold speed for recruitment of the white region (0.9kmh−1) was less than that at 35°C (1.3kmh−1). The relationship between locomotor speed and activity per minute for the red region was very similar to the relationship between speed and rate of oxygen consumption described in previous studies of lizards, and the threshold speed for recruitment of the white region was also similar to the maximal aerobic speed previously reported for this species. Hence, lizards increase speed and compensate for lower temperature by increasing intensity of activity within the red region and recruiting fibres in the white region. We suggest that compensation for muscle function at decreased body temperature may involve recruitment of greater numbers of motor units.
Nitrite and Red Cell Function in Carp: Control Factors for Nitrite Entry, Membrane Potassium Ion Permeation, Oxygen Affinity and Methaemoglobin Formation
Authors: Jensen Frank B. 
Published: April 2021

ABSTRACT
Red cell function was studied in carp by a combination of in vivo and in vitro experiments with nitrite as the perturbing agent. In vivo accumulation of nitrite caused a marked increase in the red cell methaemoglobin content, and reduced the mean cellular volume. The oxygen affinity of unoxidized haemoglobin was strongly decreased, partly as result of the elevated concentration of cellular nucleoside triphosphates and haemoglobin associated with red cell shrinkage. Red cell pH was unchanged compared to controls, but reduced when referred to constant extracellular pH and O2 saturation. The mean cellular K+ content decreased, reflecting a K+ loss from the red cells during their shrinkage. This K+ loss contributed significantly to the large plasma hyperkalaemia during nitrite exposure. In vitro experiments revealed that nitrite influx into deoxygenated red cells was much larger than into oxygenated red cells. Nitrite permeation of the red cell membrane was not inhibited by DIDS and did not change extracellular pH. Methaemoglobin (MetHb) formation was more pronounced in deoxygenated blood than in oxygenated blood, but quasi-steady states were reached, reflecting a balance between nitrite-induced MetHb formation and the action of MetHb reductase. Red cells incubated in the oxygenated state released K+, whereas a net K+ uptake occurred in deoxygenated cells. Nitrite did not change the K+ loss from oxygenated cells, but shifted the K+ uptake in deoxygenated cells to a pronounced K+ release by the time high MetHb levels were reached. Both types of red cell K+ release were inhibited by DIDS and appeared to occur via a route involving Band 3. The data are consistent with the hypothesis that a significant DIDS-sensitive K+ efflux from the red cells occurs whenever a large fraction of the haemoglobin molecules assumes an R-like quaternary structure.
Decreased Sprint Speed as A Cost of Reproduction in the LizardSceloporus Occidentals:Variation Among Populations
Authors: Sinervo Barry , Hedges Richard , Adolph Stephen C. 
Published: April 2021

ABSTRACTDecreased mobility of gravid females is thought to be an important cost of reproduction in lizards. We measured sprint speeds of female western fence lizards (Sceloporus occidentalis Baird and Girard) before and after they had oviposited. Females from two California populations were about 20% slower when gravid, females from an Oregon population were about 30% slower, and females from a Washington population were about 45 % slower, compared to their speeds after recovering from reproduction. The decrease in sprint speed persisted for several weeks after oviposition, suggesting that reproduction impairs sprint performance by affecting body condition in addition to the burdening effect of eggs.Oregon and Washington females carried more mass (both somatic and clutch mass) per unit body length than California females. On the shorter bodies of Oregon and Washington lizards, eggs may interfere with the mechanics of running, in addition to their effect on the total mass of the female. In addition, gravid females from Washington had significantly higher reproductive investment (mass of clutch relative to the mass of the female after oviposition) than Oregon and California populations. Greater reproductive investment by Washington females increases, the burden carried per unit of body length; we suggest this further impairs sprint performance.Decrements in sprint speed were not significantly correlated with level of reproductive investment (per unit body mass) among females within any of the study populations. However, the burden carried per unit body length was correlated with the sprint speed decrement among gravid females from Oregon. Comparisons within and among populations suggest that differences in morphology among northern and southern populations interact with reproductive investment to produce interpopulation differences in sprint performance for gravid females.
Physiological Properties of Afferents from Tactile Hairs on the Hindlegs of the Locust
Authors: Newland Philip L. 
Published: April 2021

ABSTRACTThe spatial distribution and physiological properties of the tactile hairs and their sensory afferents of the hindlegs of the locust Schistocerca gregaria are described. Hairs occur in a consistent position from animal to animal. Hairs on the dorsal tibia are of a greater mean length, 403.1 ±17.9 μm, than hairs on the ventral tibia, 265.2±10.44μm. Hairs on the dorsal and ventral femur are approximately 310μm long and hairs on the tarsus are shorter, approximately 200 μm. Based on their threshold responses to sinusoidal mechanical stimulation, the tactile hairs are of two basic physiological types. High-threshold hairs occur only on the proximal dorsal tibia and at the proximal base of each tibial spine, whereas low-threshold hairs are found on the femur, tibia and tarsus. High-threshold hair afferents respond phasically to imposed deflections of the hair shaft and have mean velocity thresholds of 21.1±4.2°s−1. They adapt rapidly to repetitive stimulation, after as few as 11 cycles at 5Hz. Low-threshold hairs respond in a more phaso-tonic manner to imposed deflections and have velocity thresholds of less than 3°s−1. They adapt to repetitive stimulation at a similar rate to the high-threshold hairs, but continue to respond to stimulation after 200 cycles at 5 Hz. All the hairs are directionally sensitive, with the preferred direction being oriented proximally and medially (i.e. proximally and towards the body); they are least sensitive to deflections in the opposite direction.
Field Measurements Of Hanging Flight Aerodynamics In The KestrelFalco Tinnunculus
Authors: Videler John , Groenewold Alex 
Published: April 2021

ABSTRACTHunting kestrels were observed to hang, almost without wing-flapping, in fixed positions over a sea dike. The height and position with respect to the dike profile, the wind direction and velocity and the percentage of hunting time without wing beating were recorded in 429 cases.The vertical wind angle, θ, the wind speed and its horizontal direction were measured at 13 heights up to 8.8m above the windward slope, the top and the leeward slope of the dike under various wind conditions in 225 cases. These wind profile measurements were used to estimate θ and wind speed near the hanging birds.Kestrels hanging more than 90% of the hunting time preferred a position 6.5±1.5m (S.D.) over the windward slope with sea winds blowing at 8.7± 1.5 ms-1 (S.D.) perpendicular (±30°) to the longitudinal dike axis. For these birds angle θ was approximately 6–7°.These angles are larger than expected from aerodynamic models and windtunnel measurements. The minimum gliding angle for a kestrel under steady conditions is estimated to be 5°.Hanging kestrels save two-thirds of the energy used during normal windhover-ing but have to spend 1.6 times more time to catch the same number of voles.
The Movement of the Egg Nucleus in Relation to the Sperm Aster in the Echinoderm Egg
Authors: Chambers Edward L. 
Published: April 2021

ABSTRACT
The names of O. Hertwig, H. Fol, E. Selenka, W. Roux, H. E. Ziegler, E. B. Wilson, and E. G. Conklin are associated with the classic observations on the migration of the male and female pronuclei in the inseminated egg. These workers advanced several interpretations to account for the migration. Later R. Chambers (1917) presented evidence that the aster is a gelated body and that the astral centre is the centre of centripetally directed cytoplasmic currents. On the basis of this interpretation of the aster, a reinvestigation was made of the movements of the pronuclei.
The Influence of Anterior-Pituitary and Testicular Hormones on the Sexual Maturation of Lampreys
Authors: Knowles F. G. W. 
Published: April 2021

ABSTRACT
Sexual maturity in lampreys is accompanied by modifications of the cloacal region. Thc cloacal labia become swollen by an infusion of blood and ""ducts"" form, which lead from the coelom to the mesonephric ducts. These ""ducts"" are not present in the immature adults or ammocoete larvae. These changes may be produced in the immature adults and ammocoete larvae, by injections of a mammalian-pituitary preparation. In the ammocoetes the response to even a small dose was very rapid, ducts being formed in many cases twenty-four hours after the injection of I mg. of A.P. 15 B. Testosterone and oestrone also produced these modifications in the adult, but not in the larva. Spermatogenesis of the adult was slightly affected by gonadial hormones and pituitary preparations. The gonads of the larvae were not affected by gonadial hormones or pituitary preparations in the doses used. The rapidity of the cloacal response to the injections of pituitary preparations in ammocoetes suggests that this response is of a direct nature. The absence of changes in the gonads of injected ammocoetes supports this view.
Effects of Environmental Factors on Exercise In Fish
Authors: Randall David , Brauner Colin 
Published: April 2021

ABSTRACT
The critical swimming velocity of fish is affected by environmental conditions and the highest swimming speed is obtained only under specific circumstances. The mechanisms causing a reduction in exercise capacity depend on the type of environmental change. Acid waters exert an effect by reducing oxygen transport capacity, whereas reduced temperatures act largely on muscle contractility. Alkaline conditions and salinity change may affect both gas transport and muscle contractility.
A fish must operate over a wide range of internal and external conditions and must possess both short- and long-term mechanisms to maintain function under a wide variety of conditions. These mechanisms may be part of the immediate reflex arsenal available to the fish (for example, catecholamine release) or they may be mechanisms induced during acclimation. The nature of the acclimation process is an indication of what may be limiting exercise under a particular set of circumstances.
The concept of symmorphosis, especially when applied to ectotherms, needs to be viewed in a broader context. A symmetry of component parts may exist such that structures are designed to satisfy functional requirements for operation over a wide range of conditions, rather than optimally for a given set of conditions. This must involve compromises in design, especially for ectotherms such as fish. Thus, the more variable the conditions under which a system must operate, the less apparent it will be that symmorphosis exists between the component parts.
Conditions for Oxygen and Substrate Transport in Muscles in Exercising Mammals
Authors: Hoppeler Hans , Billeter R. 
Published: April 2021

ABSTRACT
The structural conditions relevant for metabolite exchange in anaerobic and aerobic work conditions in muscle tissue are reviewed. High-intensity non-steadystate exercise is supported by the phosphocreatine pool, which serves as a shuttle for high-energy phosphates produced by glycolysis and by aerobic metabolism. This is achieved through the intermediary of a topologically organized creatine kinase isozyme system. The muscle capillary network supplies substrate and environmental oxygen to the mitochondria. The network is quantitatively matched to the muscle oxidative capacity, determined structurally by mitochondrial volume. Capillary hematocrit, erythrocyte spacing and oxygen saturation of myoglobin are critical variables for oxygen release from microvessels. Myoglobin greatly helps intracellular oxygen transfer as, under aerobic work conditions, it keeps intracellular oxygen tension low and uniform in the muscle fibers. During sustained submaximal work, muscle cells are fueled by both endogenous (triglycerides and glycogen) and circulatory (lactate, glucose and fatty acids) substrates. A lactate shuttle in which lactate may move through the circulation, as well as directly from fiber to fiber, provides many of the carbohydrate-derived carbon skeletons for terminal oxidation. Glucose is taken up from the interstitial space by facilitated diffusion, mostly mediated by a glucose transporter (GLUT4) that is translocated from an intracellular location to the sarcolemma by activity and insulin. Extramyocellular transport of fatty acids is mediated by albumin, while fatty-acid-binding proteins are held responsible for intracellular fatty acid transport.
Gravity-Induced Changes in Propulsion of Paramecium Caudatum: a Possible Role of Gravireception in Protozoan Behaviour
Authors: Ooya Mayumi , Mogami Yoshihiro , Izumi-Kurotani Akemi , Baba Shoji A. 
Published: April 2021

ABSTRACT
The swimming behaviour of Paramecium was analyzed under natural and experimental hypergravity conditions. Paramecium that swam upwards (in the opposite direction to the gravitational force) along a straight path (straight swimmers) swam more slowly than those swimming downwards. This dependence of the swimming velocity on its direction relative to gravity can be partly interpreted as the consequence of sinking due to gravity if the propulsive force does not vary. The effect was different for Paramecium swimming along a circular path (curved swimmers). The difference in velocity between those swimming upwards and those swimming downwards was substantially smaller than would have been expected from sinking effects with invariant propulsion even after correcting for maximal hydrodynamic wall effects, indicating that Paramecium compensate for sinking caused by gravity by controlling their propulsion. The propulsive velocity evaluated by vector calculus increased both as Paramecium swam more sharply upwards and as the experimental gravitational force was increased. The dependence of propulsion on the swimming direction and on gravity was reduced in a high-density medium of nearly neutral buoyancy, suggesting that the site of gravireception is unlikely to be in the interior of the cell. The differences between straight and curved swimmers are discussed in terms of rapid adaptation of gravireceptors in the cell membrane, desensitization of mechanosensory channels and hyperactivation of ciliary activity in straight swimmers.