The Journal of physiology.
Publisher:
Cambridge Univ. Press.. Oxford : Blackwell : Cambridge Univ. Press
Frequency: Twenty-seven no. a year, 2002-
Country: England
Language: English
Author(s):
Physiological Society (Great Britain)
Start Year:1878 -
ISSN:
0022-3751 (Print)
1469-7793 (Electronic)
0022-3751 (Linking)
1469-7793 (Electronic)
0022-3751 (Linking)
Impact Factor
5.5
2023
| NLM ID: | 0266262 |
| (DNLM): | J35160000(s) |
| (OCoLC): | 01754742 |
| Coden: | JPHYA7 |
| LCCN: | 49034373 |
| Classification: | W1 JO837 |
Pre-loading large volume oral electrolytes: tracing fluid and ion fluxes in horses during rest, exercise and recovery. Exercise results in rapid and large extracellular to intracellular fluid shifts, as well as significant sweating losses of water and ions. It is unknown whether ions within oral electrolyte supplements are taken up by muscle (and other soft tissues) and whether oral supplementation can effectively offset sweating losses. Pre-loading with 8 L of a balanced hypotonic electrolyte supplement attenuated extracellular fluid losses, increased exercise duration and increased sweating fluid and ion losses during submaximal exercise. Supplemented electrolytes appear in skeletal muscle within 1 h after...
Acetazolamide attenuates transvascular fluid flux in equine lungs during intense exercise. During intense exercise in horses the transvascular fluid flux in the pulmonary circulation (Jv-a) represents 4% of cardiac output (Q). This fluid flux has been attributed to an increase in pulmonary transmural hydrostatic forces, increases in perfused microvascular surface area, and reversible alterations in capillary permeability under conditions of high flow and pressure. Erythrocyte fluid efflux, however, accounts for a significant fraction of Jv-a. In the lung the Jacobs-Stewart cycle occurs with diffusion of CO2 into alveolar space with possible accompanying chloride (Cl-) and water ...
Development of baroreflex function and hind limb vascular reactivity in the horse fetus. This study investigated, in vivo, the mechanisms underlying the development of cardiovascular function in the horse fetus, with particular relevance to baroreflex function and hind limb vascular arterial reactivity to constrictor agonists. Under general anaesthesia, vascular catheters were inserted and a Transonic flow probe was implanted around one of the metatarsal arteries of 13 horse fetuses, either at 0.6 of gestation (n= 6) or at 0.9 of gestation (n= 7, term approximately 335 days). At least 5 days after surgery, pressor, vasoconstrictor and cardiac chronotropic responses to exogenous bo...
Transvascular fluid flux from the pulmonary vasculature at rest and during exercise in horses. Exercise causes changes in pulmonary haemodynamics through redistribution of blood flow, increase in the pulmonary surface area, and increase in pulmonary vascular pressures. These changes contribute to the increase in fluid exchange across the alveolar-capillary barrier. To determine the extent of the fluid exchange across the alveolar-capillary barrier at rest and during exercise, six horses were exercised on a high-speed treadmill until fatigue. Arterial and mixed venous blood were sampled at rest and during exercise and recovery. Blood volume changes across the lung (DeltaBV; measured in p...
Development of cardiovascular function in the horse fetus. In mammals, the mechanisms regulating an increase in fetal arterial blood pressure with advancing gestational age remain unidentified. In all species studied to date, the prepartum increase in fetal plasma cortisol has an important role in the maturation of physiological systems essential for neonatal survival. In the horse, the prepartum elevation in fetal cortisol and arterial blood pressure are delayed relative to other species. Hence, the mechanisms governing the ontogenic increase in arterial blood pressure in the horse fetus may mature much closer to term than in other fetal animals. In ...
Structural changes in loaded equine tendons can be monitored by a novel spectroscopic technique. This study aimed to investigate the preferential collagen fibril alignment in unloaded and loaded tendons using elastic scattering spectroscopy. The device consisted of an optical probe, a pulsed light source (320-860 nm), a spectrometer and a PC. Two probes with either 2.75 mm or 300 microm source-detector separations were used to monitor deep and superficial layers, respectively. Equine superficial digital flexor tendons were subjected to ex vivo progressive tensional loading. Seven times more backscattered light was detected parallel rather than perpendicular to the tendon axis with the 2.7...
Postnatal cardiovascular function after manipulation of fetal growth by embryo transfer in the horse. This study used between-breed embryo transfer in the horse to investigate the effects of maternal size and uterine capacity on fetal growth and postnatal cardiovascular and neuroendocrine functions. Equine embryos were transferred to establish eight Thoroughbred-in-Thoroughbred (TinT), seven Pony-in-Pony (PinP), five Thoroughbred-in-Pony (TinP) and eight Pony-in-Thoroughbred (PinT), pregnancies. Maternal and foal weights and placental microscopic area were measured at birth. At 6 days of postnatal life, arterial blood pressure and heart rate were monitored and blood samples were taken for horm...
Ontogenic and nutritionally induced changes in fetal metabolism in the horse. 1. Using the Fick principle and tracer methodology, the metabolic rates of chronically catheterized fetal foals (n = 24) were measured at different gestational ages during the second half of gestation and in response to maternal fasting for 36 h in late gestation (n = 4, term approximately 335 days). 2. Absolute rates of umbilical blood flow, fetal glucose utilization and umbilical uptake of oxygen (O2) and glucose increased from mid-gestation to 300 days and then plateauxed until term. The absolute rate of umbilical lactate uptake was significant after, but not before, 280 days of gestation. ...
Signalling pathway for histamine activation of non-selective cation channels in equine tracheal myocytes. 1. The signalling pathway underlying histamine activation of non-selective cation channels was investigated in single equine tracheal myocytes. Application of histamine (100 microM) activated the transient calcium-activated chloride current (ICl(Ca)) and sustained, low amplitude non-selective cation current (ICat). The H1 receptor antagonist pyrilamine (10 microM) blocked activation of ICl(Ca) and ICat. Simultaneous application of histamine (100 microM) and caffeine (8 mM) during H1 receptor blockade activated ICl(Ca), but not ICat. Neither the H2 receptor antagonist cimetidine (20 microM) nor...
Oxygen-dependent K+ influxes in Mg2+-clamped equine red blood cells. 1. Cl--dependent K+ (86Rb+) influxes were measured in oxygenated and deoxygenated equine red blood cells, whose free [Mg2+]i had been clamped, to examine the effect on O2 dependency of the K+-Cl- cotransporter. 2. Total [Mg2+]i was 2.55 +/- 0.07 mM (mean +/- s.e.m. , n = 6). Free [Mg2+]i was estimated at 0.45 +/- 0.04 and 0.68 +/- 0. 03 mM (mean +/- s.e.m., n = 4) in oxygenated and deoxygenated red cells, respectively. 3. K+-Cl- cotransport was minimal in deoxygenated cells but substantial in oxygenated ones. Cl--dependent K+ influx, inhibited by calyculin A, consistent with mediation via the ...
The equine periodic paralysis Na+ channel mutation alters molecular transitions between the open and inactivated states. 1. The Na+ channel mutation associated with equine hyperkalaemic periodic paralysis (HPP) affects a highly conserved phenylalanine residue in an unexplored region of the alpha-subunit. This mutation was introduced into the rat skeletal muscle Na+ channel gene at the corresponding location (i.e. F1412L) for functional expression and characterization in Xenopus oocytes. 2. In comparison with wild-type (WT) channels, equine HPP channels showed clear evidence for disruption of inactivation: increased time-to-peak current, slowed rates of whole-cell current decay, significant increases in sustained...
Anion secretion induced by capacitative Ca2+ entry through apical and basolateral membranes of cultured equine sweat gland epithelium. 1. Anion secretion induced by capacitative Ca2+ entry through apical and basolateral membranes of cultured equine sweat gland epithelium was studied using the short-circuit current (Isc) technique. 2. Thapsigargin induced an increase in Isc that could be inhibited when external Ca2+ was chelated by EGTA. 3. The inhibition of the thapsigargin-induced Isc could be reversed by re-addition of Ca2+ to apical or basolateral solutions. The magnitude of the reactivated Isc depended predominantly on basolateral Ca2+ concentration. 4. The magnitude of the reactivated Isc upon basolateral Ca2+ addition i...
Nitric oxide and exercise in the horse. 1. The effects of exercise on the production rate of nitric oxide (NO) in exhaled air (VNO) and the effects of inhaled NO (80 p.p.m.) on cardiovascular and respiratory parameters were investigated in five Throughbred horses. 2. The concentration of NO ([NO]) in exhaled air collected from within the nasal opening was lower when collected at a high flow rate of 80 l min-1 than at a low flow rate of 20 l min-1: when trotting at 3.7 m s-1 the values were 0.78 +/- 0.15 and 1.23 +/- 9.14 p.p.b., respectively, and when cantering at 9 m s-1 the values were 1.69 +/- 0.31 and 2.25 +/- 0.32 p.p.b., respe...
Ionic mechanisms of Ca(2+)-dependent electrolyte transport across equine sweat gland epithelium. 1. The ionic mechanism involved in Ca(2+)-stimulated electrolyte transport in cultured equine sweat gland epithelial cells was studied using the short-circuit current (ISC) technique. 2. Microscopy revealed that the cultured cells grown on Millipore filters formed polarized monolayers with tight junctions. Monolayers exhibited a mean transepithelial resistance of 333.9 +/- 40.4 omega cm2. 3. Ca(2+)-mobilizing agents, A23187 (1 microM) or thapsigargin (0.01-1 microM), stimulated ISC while forskolin exerted little effect on the ISC. 4. Replacement of external Cl- by gluconate significantly reduc...
The effects of locomotor-respiratory coupling on the pattern of breathing in horses. 1. To investigate the effect of locomotor activity on the pattern of breathing in quadrupeds, ventilatory response was studied in four healthy horses during horizontal and inclined (7%) treadmill exercise at different velocities (1.4-6.9 m s(-1)) and during chemical stimulation with a rebreathing method. Stride frequency (f(s)) and locomotor-respiratory coupling (LRC) were also simultaneously determined by means of video recordings synchronized with respiratory events. 2. Tidal volume (V(T)) was positively correlated with pulmonary ventilation (V(E)) but significantly different linear regressi...
Voltage-dependent calcium currents and cytosolic calcium in equine airway myocytes. 1. The relationship between voltage-dependent calcium channel current (I(Ca)) and cytosolic free calcium concentration ([Ca2+]i) was studied in fura-2 AM-loaded equine tracheal myocytes at 35 degrees C and 1.8 mM Ca2+ using the nystatin patch clamp method. The average cytosolic calcium buffering constant was 77 +/- 3 (n = 14), and the endogenous calcium buffering constant component is likely to be between 15 and 50. 2. I(Ca) did not evoke significant calcium-induced calcium release (CICR) since (i)[Ca2+]i scaled with the integrated I(Ca) over the full voltage range of evoked calcium currents, ...
Regulation of granule size in human and horse eosinophils by number of fusion events among unit granules. 1. We have investigated the granule size distributions in human and horse eosinophils by time-resolved patch-clamp capacitance measurements. 2. During exocytosis of single granules the electrical capacitance of the plasma membrane increases in discrete steps. The steps in horse cells are about six times larger than those in human cells in accordance with the difference in granule size. 3. In both species a multimodal capacitance step size distribution is observed with a first peak at 6-7 fF corresponding to granules with a diameter of about 450-500 nm and a surface area of about 0.7 microns2, ...
Estimation of the carnosine content of different fibre types in the middle gluteal muscle of the thoroughbred horse. 1. Skeletal muscle samples were obtained by needle biopsy from one of two depths of the m. gluteus medius in a group of twenty race-trained thoroughbred horses. 2. The content of carnosine was determined in each muscle sample, part of which was used for histochemical analysis. Fibres were classified as type I, type IIA or type IIB on the basis of the pH dependent lability of the myosin ATPase reaction. 3. Muscle samples with a higher type II fibre section area (FSA) have a higher carnosine content than those with a higher type I FSA. 4. Multiple linear regression analysis was used to estimate ...
Maximum velocity of shortening of three fibre types from horse soleus muscle: implications for scaling with body size. 1. To explore how maximum velocity of shortening (Vmax) of fibres varies within one muscle and how Vmax varies with body size, we measured Vmax of muscle fibres from soleus muscle of a large animal, the horse. 2. Vmax was determined by the slack test on skinned single muscle fibres at 15 degrees C during maximal activation (pCa = 5.2). The fibre type was subsequently determined by a combination of single-cell histochemistry and gel electrophoresis of the myosin light chains. 3. Vmax values for the type I, IIA and IIB muscle fibres were 0.33 +/- 0.04 muscle lengths/s (ML/s) (+/- S.E.M., n = 6),...
Left ventricular oxygen extraction during submaximal and maximal exertion in ponies. 1. Left ventricular (LV) myocardial O2 extraction was studied in five healthy ponies which had catheters implanted in the great cardiac vein and main pulmonary artery 15-30 days before the study. The abdominal aorta was percutaneously catheterized to sample arterial blood. 2. In addition, phasic LV and aortic pressures, LV dP/dtmax and rate-pressure product were also studied; dP/dtmax is the maximal rate of rise of the left ventricular pressure during the isovolumic phase, and is considered an index of myocardial contractility. Measurements were made at rest (control) and during adenosine infu...
Heterogeneity of amino acid transport in horse erythrocytes: a detailed kinetic analysis of inherited transport variation. 1. Thoroughbred horses were divisible into five distinct amino acid transport subgroups on the basis of their erythrocyte permeability to L-alanine, measured uptake rates ranging from 5 to 625 mumol l cells-1 h-1 (0.2 mM-extracellular L-alanine, 37 degrees C). 2. Erythrocytes from animals belonging to the lowest L-alanine permeability subgroup (5-15 mumol l cells-1 h-1) (transport-deficient type) exhibited slow nonsaturable transport of this amino acid. In contrast, cells from horses of the four transport-positive subgroups possessed additional high-affinity (apparent L-alanine Km (Michaelis c...
Transmural coronary vasodilator reserve and flow distribution during maximal exercise in normal and splenectomized ponies. 1. Transmural distribution of myocardial blood flow was studied using 15 micron diameter radionuclide-labelled microspheres in six normal ponies and nine splenectomized ponies at rest, and during maximal exercise performed without as well as with adenosine infusion (3 microM kg-1 min-1). The splenectomized ponies were also studied during submaximal exercise performed at 75% of the workload. 2. Maximal exertion in normal ponies increased heart rate (348%), mean arterial blood pressure (40.9%), rate-pressure product (563%), arterial O2 content (43.2%), and mean pulmonary artery pressure (247%). ...
Kidney function in rats with corticomedullary nephrocalcinosis: effects of alterations in dietary calcium and magnesium. Single-nephron and whole-kidney function were studied in female rats with corticomedullary nephrocalcinosis, and in animals where the lesion had been prevented either by a dietary magnesium supplement or by using a diet with a calcium:phosphorus ratio in excess of 1. At the single-nephron level, rats with nephrocalcinosis had prolonged tubular fluid transit times. Proximal transit time was 19.42 +/- 1.98 (mean +/- S.E. of mean) vs. 11.58 +/- 0.19 s for controls; distal transit time was 62.64 +/- 9.16 vs. 31.50 +/- 1.03 s for controls. Although single-nephron function is altered in nephrocalcin...
Blood flow to the respiratory and limb muscles and to abdominal organs during maximal exertion in ponies. Using radionuclide-labelled microspheres, 15 micron in diameter, we studied blood flow in the respiratory muscles (diaphragm and intercostal muscles), abdominal organs (adrenal glands, kidneys, pancreas, spleen and the small and large intestines), muscles of propulsion (gluteus medius and biceps femoris), and other working (triceps brachii and longissimus dorsi lumborum) and non-working (temporal and masseter) muscles of ponies at rest and during maximal exercise performed on a treadmill. During maximal exercise heart rate, whole body O2 consumption, cardiac output and mean aortic pressure inc...
The effect of training and detraining on muscle composition in the horse. 1. Percutaneous needle biopsies were obtained from six limb muscles in six horses before and during a training programme of 10 or 15 weeks designed to involve both aerobic and anaerobic work. In a subsequent detraining period, biopsies were also taken after 5 and 10 weeks. 2. Samples were analysed biochemically for enzyme activity of lactic dehydrogenase (LDH), creatine phosphokinase (CPK), aldolase (ALD), citrate synthase (CS), aspartate aminotransferase (AST), and alanine aminotransferase (ALT) and for glycogen content. Fibre typing was carried out histochemically before and 10 weeks after c...