The origin of life took place in the ancient sea where the ionic concentration is thought to have been somewhat lower than that of the present day seas. This may partly explain why most vertebrate species have plasma ionic concentrations roughly one-third of seawater. Exceptions are primitive marine cyclostomes whose plasma is almost identical to seawater, and marine cartilaginous fishes that accumulate urea in plasma to increase osmolarity to a seawater level. The mechanisms for regulation of water and electrolyte balance should have evolved from these animals into those of more advanced ones in which plasma ions are regulated to one-third of seawater irrespective of the habitat. Although most extant terrestrial and aquatic animals maintain similar plasma osmolarity and ionic concentrations, the mechanisms of regulation differ greatly among different groups of animals according to their habitat. An outstanding difference is that while plasma Na⁺ concentration is a primary factor of regulation in terrestrial mammals and birds, blood volume is most strictly regulated in aquatic teleost fishes. Consistently, while an increase in plasma osmolarity (cellular dehydration) is a major dipsogenic stimulus for birds and mammals, hypovolemia (extracellular dehydration) is a much stronger stimulus for elicitation of drinking in teleost fishes. Furthermore, fish cells in culture are tolerant to changes in environmental osmolarity compared with mammalian cells, further suggesting a secondary role of plasma osmolarity as a target of regulation in fishes. A secondary role of blood volume for body fluid regulation in birds is further assessed by the fact that volume receptors for thirst, salt gland secretion, and vasotocin secretion are localized in the extravascular, interstitial space in some species of birds. All terrestrial animals including mammals have derived from the fishes in phylogeny, during which the mechanisms for body fluid regulation underwent adaptive evolution in the course of transition from aquatic to terrestrial life. Therefore, much can be learned from comparative studies of body fluid regulation that reveals the diversity and uniformity of the mechanisms. In this review, important comparative studies that may contribute to an understanding of body fluid regulation throughout vertebrate species will be summarized.

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The purpose of this study was to investigate the effects of staying at a moderate altitude (2,300 m, 7 d) on the levels of plasma nitrite, exhaled nitric oxide (NO), malondialdehyde (MDA) and superoxide dismutase (SOD). Measurements were obtained from 9 female (mean age 18.3 ± 2) and 9 male (mean age 19.3 ± 3.7) cross-country volunteer skiers: before, during (1st day, 7th day) and after staying at a moderate altitude. Exhaled nitric oxide levels were measured only before and after staying at the altitude. Nitrite levels increased throughout the stay at the altitude, while MDA levels decreased. In parallel with the nitrite levels, SOD activities were also found to have increased. Exhaled NO values were decreased after the stay at the moderate altitude. These results show that altitude hypoxia causes decreased in NO levels in the lung but increased systemic NO levels in the blood due to inhibition of erythrocyte lipid peroxidation.

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In the circular muscle of guinea-pig gastric antrum, the effects of removal and reapplication of K⁺ and Cl⁻ were studied on the slow wave, which consists of the lower, first and upper, second components. The first component appeared to be triggered by the driving potential generated in the interstitial cells. K⁺ removal slightly depolarized the membrane, increased frequency, and shortened the first component and driving potential, and K⁺ reapplication hyperpolarized and prolonged these potentials transiently. Ouabain abolished the K⁺-induced hyper-polarization but had no inhibitory effect on the K⁺-induced potentiation. The K⁺-induced prolongation was much reduced in Ca²⁺-deficient and increased in Ca²⁺-excess solution. BAPTA-AM, thapsigargin, and cyclopiazonic acid shortened the slow wave and inhibited the K⁺-induced prolongation but did not block the slow wave. Effects of Cl⁻ removal were stronger than K⁺ removal in shortening and increasing the frequency. In Cl⁻-deficient solution, no prolongation was observed on K⁺ reapplication. Although no conclusive evidence was obtained as to the ionic mechanism involved in the effects of K⁺ or Cl⁻ removal and reapplication, a possibility is considered that the sarcoplasmic reticulum is involved in determining the duration of the driving potential and the first component of the slow wave.

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The purpose of the present study was to examine the response of excess CO₂ output to short-term intensive exercise in sprinters (SPR) and long-distance runners (LDR). End-tidal CO₂ pressure (PETCO₂) increased up to about 20 s postexercise and then returned to the resting level at about 2–3 min postexercise. Thereafter, PETCO₂ remained below the resting level. V˙CO₂ excess, defined as the difference between V˙CO₂ and V˙O₂ was integrated from the start of exercise until PETCO₂ returned to the resting level. This integrated V˙CO₂ excess was defined as the first phase of CO₂ excess (1st CO₂ excess). The subsequent integrated V˙CO₂ excess until 10 min postexercise was defined as the second phase of CO₂ excess (2nd CO₂ excess). The ratio of 1st CO₂ excess to the lactate rise from rest to the peak value was significantly lower in SPR than in LDR, whereas 2nd CO₂ excess was significantly greater in SPR than in LDR. The decrease in PETCO₂ at 10 min postexercise was significantly larger in SPR than in LDR. The 2nd CO₂ excess was closely related to the decrease in PETCO₂. The results in the second phase suggest that the difference in the response of excess CO₂ output is derived from the difference in the respiratory chemosensitivity to lactic acid rise.

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We investigated the relationship between the effects of ischemic preconditioning (IPC) and Ca²⁺ preconditioning (CPC) on reperfusion-induced arrhythmias. In the control group (noPC), Langendorff-perfused rat hearts were subjected to 5-min zero-flow global ischemia (I) followed by 15-min reperfusion (I/R). In ischemic preconditioning groups (IPC), the hearts were subjected to three cycles of 3-min global ischemia and 5-min reperfusion. In the CPC group, the hearts were exposed to three cycles of 3-min perfusion of higher Ca²⁺ (2.3 mmol/l Ca²⁺) followed by 5-min perfusion of normal 1.3 mmol/l Ca²⁺, and the hearts were then subjected to I/R. Verapamil was administered in several hearts of the IPC group (VR+IPC). Ventricular arrhythmias upon reperfusion were less frequently seen in the IPC and CPC groups than in the noPC and VR+IPC groups. IPC and CPC could attenuate conduction delay and enhance shortening of the monophasic action potential duration during ischemia. The ventricular fibrillation threshold measured at 1-min reperfusion was significantly higher in the IPC and CPC groups than in the noPC and VR+IPC groups. Verapamil completely abolished the salutary effects of IPC. These results demonstrate that Ca²⁺ plays an important role in the antiarrhythmic effect of IPC during reperfusion.

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Secretin stimulates bicarbonate secretion from pancreatic duct cells, but what influence secretin exerts on intestinal tissues remains to be clarified. The aim of this study is to examine effects of secretin on ion transport in intestinal epithelial Caco-2 cells. We mounted monolayers of Caco-2 cells grown on permeable supports for 21–28 d in a Ussing chamber and measured short-circuit currents (I_sc). Addition of secretin (5–100 nM) to the basolateral solution dose-dependently induced biphasic increases of I_sc (transient and sustained phase). Dibutyryl cyclic AMP (200 μM), forskolin (10 μM), and 3-isobutyl-1-methylxanthine (IBMX, 1 mM) also induced I_sc responses similar to the administration of secretin. Addition of 5-nitro-2-(3-phenylpropylamino) benzoic acid (NPPB, 100 μM) or benzamil (100 μM) to the apical solution markedly reduced the secretin-induced I_sc increase in the transient phase. A selective antagonist of cAMP-dependent protein kinase (PKA), N-[2-(p-bromocinnamylamino)ethyl]-5-isoquinolinesulfonamide (H-89, 1 μM), and a membrane permeable Ca²⁺ chelator, 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid tetrakis(acetoxymethyl ester) (BAPTA/AM, 10 μM) reduced the secretin-induced I_sc. Basolateral addition of 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS, 1 mM) suppressed the sustained phase I_sc increase. Secretin also induced alkalinization of the apical solution (ΔpH, 0.053 ± 0.013). The alkalinization did not occur when DIDS (1 mM) was added to the basolateral solution or Na⁺ was removed from the solutions. Taken together, our observations suggest: (1) secretin stimulates a benzamil-sensitive Na⁺ influx and an NPPB-sensitive Cl⁻ efflux across the apical membrane through PKA-dependent and Ca²⁺-sensitive pathways; and (2) secretin also induces alkalinization of the apical solution through the activation of a DIDS-sensitive Na⁺-HCO₃⁻ cotransport in the basolateral membrane of Caco-2 cells.

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The present study was undertaken to evaluate the effects of hypoxia and hypercapnia on circulatory parameters during acute normovolemic hemodilution. Cats anesthetized with a mixture of α-chloralose and urethane were maintained by positive pressure ventilation. Muscles were paralysed by intramuscular vecuronium (0.1 mg/kg) to eliminate reflex respiratory movements. Cats were exposed to hypoxia (12% O₂ and 7% O₂) and hypercapnia (4% CO₂ and 7% CO₂) at normal hematocrit (Ht 40.1 ± 2.8%) and then at graded levels of normovolemic hemodilution (Ht 24.0 ± 2.0% and Ht 13.0 ± 1.5%, respectively). Left ventricular pressure (LVP), LV dP/dt_max, arterial blood pressure (ABP), heart rate (HR), and right atrial pressure (RAP) were recorded on a polygraph. Cardiac output (CO) was measured using a cardiac output computer. Hemodilution per se did not produce any significant change in ABP, RAP or LV dP/dt_max, however, it produced a significant rise in HR and a significant fall in total peripheral resistance (TPR). Exposure to hypoxic gas mixtures caused significant increases in HR and CO at control Ht; but after hemodilution it caused the reverse effects. Hypercapnia did not produce any significant effect on ABP, LV dP/dt_max or RAP either at control Ht or after hemodilution. Hypercapnia produced a fall in HR, CO and stroke volume (SV) at normal Ht and percent fall in HR response was enhanced following hemodilution. The reversal of chronotropic response to hypoxia and enhanced bradycardia response to hypercapnia, under conditions of acute normovolemic hemodilution would be deleterious as the tissues would become more hypoxic. Such a response may be attributed to altered control mechanisms under such conditions of severe stress.

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Osmotic swelling induces the release of intracellular ATP in a number of cell types. In the immediate vicinity of the cell surface, released ATP has been shown to reach a concentration high enough to stimulate P2-purinergic receptors in a human epithelial cell line, Intestine 407. The role of released ATP in the regulatory volume decrease (RVD) after cell swelling was thus studied in Intestine 407 cells. The RVD was suppressed by an ATP hydrolyzing enzyme, apyrase, or by a purinergic receptor antagonist, suramin. Extracellular application of ATP accelerated the RVD rate in a concentration-dependent manner. An increase in the cytosolic free-Ca²⁺ concentration was induced by a hypotonic challenge, and the swelling-induced Ca²⁺ response was partially suppressed by apyrase or suramin. A rise in cytosolic Ca²⁺ was also induced by extracellular application of ATP or UTP, but not ADP, 2-methylthio-ATP or α,β-methylene ATP. The ATP-induced Ca²⁺ response was blocked by suramin. Therefore, it is concluded that RVD is facilitated by ATP, which is released upon cell swelling, by augmenting intracellular Ca²⁺ rise via the stimulation of purinergic (P2Y₂) receptors in the human epithelial cell.

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The inhibitory effect of central administration of calcitonin-gene related peptide (CGRP) on pancreatic secretion stimulated by bile-pancreatic juice diversion was determined in conscious rats. Rats were prepared with separate cannulae for draining bile and pancreatic juice and with a duodenal cannula and an extrajugular vein cannula. In addition, another cannula was stereotactically implanted into the left lateral cerebral ventricle. Rats were placed in restraint cages and experiments were conducted 4 d after the operation without anesthesia. An injection of CGRP (1 nmol/10 μl) into the left lateral cerebral ventricle (i.c.v.) inhibited pancreatic secretion as well as cholecystokinin (CCK) release induced by bile-pancreatic juice diversion. Intravenous infusion of α- and β-adrenergic receptor antagonist, phentolamine and propranolol did not reverse the inhibition of pancreatic secretion. Intravenous infusion of CGRP did not affect pancreatic secretion or plasma CCK concentrations. The inhibitory action of central CGRP (i.c.v.) on pancreatic secretion and CCK release stimulated by bile-pancreatic juice diversion is partially mediated by an α-adrenergic mechanism, although its precise mechanism has not been elucidated.

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The inwardly rectifying ATP-regulated K⁺ channel with an inward conductance of about 90 pS in the surface membrane of cultured opossum kidney proximal tubule (OKP) cells is activated at least in part by protein kinase A (PKA). In this study, we examined the effects of protein serine/threonine phosphatase types 1 (PP-1) and 2A (PP-2A) on activity of the K⁺ channel using the patch-clamp technique. In cell-attached patches, channel activity was enhanced by the application of okadaic acid (OA, 1 μM), a membrane-permeable inhibitor of PP-1 and PP-2A, to the bath solution. This enhancement was abolished by the pretreatment of cells with KT5720 (200 nM), a specific inhibitor of PKA. In inside-out patches, channel activity which could be maintained in the presence of ATP (3 mM) in the bath solution was also increased by the addition of OA (1 μM), and the OA-induced increase in channel activity was partially prevented in the presence of KT5720 (200 nM). Direct application of either PP-1 (1 U/ml) or PP-2A (1 U/ml) to the cytoplasmic surface of the patch membrane inhibited channel activity maintained by ATP (3 mM) in inside-out patches. Moreover, channel activity stimulated by PKA (20 nM) in the presence of ATP (3 mM) was also inhibited by the application of either PP-1 (1 U/ml) or PP-2A (1 U/ml). These results indicate that the OA-sensitive protein phosphatase is involved in the regulation of channel activity, and suggest that both PP-1 and PP-2A are candidates responsible for the inhibition of channel activity through dephosphorylation of the PKA-mediated protein phosphorylation.

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Caffeine causes a considerable O₂ waste for positive inotropism in myocardium by complex pharmacological mechanisms. However, no quantitative study has yet characterized the mechanoenergetics of caffeine, particularly its O₂ cost of contractility in the E_max-PVA-VO₂ framework. Here, E_max is an index of ventricular contractility, PVA is a measure of total mechanical energy generated by ventricular contraction, and VO₂ is O₂ consumption of ventricular contraction. The E_max-PVA-VO₂ framework proved to be powerful in cardiac mechanoenergetics. We therefore studied the effects of intracoronary caffeine at concentrations lower than 1 mmol/l on left ventricular (LV) E_max and VO₂ for excitation-contraction (E-C) coupling in the excised cross-circulated canine heart. We enhanced LV E_max by intracoronary infusion of caffeine after β-blockade with propranolol and compared this effect with that of calcium. We obtained the relation between LV VO₂ and PVA with E_max as a parameter. We then calculated the VO₂ for the E-C coupling by subtracting VO₂ under KCl arrest from the PVA-independent (or zero-PVA) VO₂ and the O₂ cost of E_max as the slope of the E-C coupling VO₂-E_max relation. We found that this cost was 40% greater on average for caffeine than for calcium. This result, for the first time, characterized integratively cardiac mechanoenergetics of the O₂ wasting effect of the complex inotropic mechanisms of intracoronary caffeine at concentrations lower than 1 mmol/l in a beating whole heart.

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The effects of corticosteroids on synaptic transmission in the rat dorsolateral septal nucleus (DLSN) were examined, in vitro, by using intracellular and voltage-clamp recording methods. Prednisolone (100 μM) increased the amplitude of excitatory postsynaptic potential (EPSP) and depressed both fast and slow inhibitory postsynaptic potentials (IPSP). Under voltage-clamp conditions, prednisolone (100 μM) increased the amplitude of excitatory postsynaptic current (EPSC) and depressed the fast and slow inhibitory postsynaptic currents (IPSCs). Corticosterone (100 μM) mimicked the effects of prednisolone on the postsynaptic currents (PSCs). To examine the direct effects of prednisolone on the EPSC and slow IPSC, the fast IPSC was blocked by bicuculline (20 μM). Under these experimental conditions, prednisolone (100 μM) did not alter the isolated EPSC but depressed slow IPSC by 22 ± 3% (n = 10). The fast IPSC was isolated by pretreatment with kynurenic acid and CGP55845A, where the EPSC and slow IPSC were blocked. Prednisolone (100 μM) depressed the isolated fast IPSC in DLSN neurons. Prednisolone (100 μM) did not change either the inward current produced by glutamate or the outward current produced by γ-aminobutyric acid (GABA). The results suggest that corticosteroids facilitate excitatory synaptic transmission in the DLSN by reducing the release of GABA from the presynaptic nerve terminals of interneurons.

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In order to test whether an improvement of maximal sprinting speed after creatine (Cr) supplementation was due to the increase of stride frequency (SF), stride length (SL) or both, 7 subjects ran 4 consecutive sprints after 1 week of placebo or Cr supplementation. SF and SL were assessed by a triaxial accelerometer. Compared to the placebo, Cr induced an increase of running speed (+1.4% p < 0.05) and SF (+1.5%, p < 0.01), but not of SL. The drop in performance following repeated sprints was partially prevented by Cr. In conclusion, exogenous Cr enhanced sprinting performance by increasing SF. This result may be related to the recent findings of shortening in muscular relaxation time after Cr supplementation.

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In human epithelial cell lines, whole-cell swelling-activated Cl⁻ current was not directly correlated to cell volume per se, membrane tension or hydrostatic pressure. The current density exhibited a relation described by a Boltzmann function to the square of the cell diameter. Cytochalasin D enhanced the volume sensitivity. These results suggest that the activation mechanism of volume-sensitive Cl⁻ channel is related to cytoskeleton-dependent membrane spring energy in human epithelial cells.

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Cells that are apoptotic and comprise less than 2% of the total cellular population are difficult to detect by conventional methods (i.e., DNA ladder). We discuss a new methodological technique, PCR-amplified DNA ladder, to detect very low levels of DNA fragmentation (indicative of apoptosis) in a myocardial infarct heart failure model. Results and methodology are contrasted with the traditional DNA ladder technique.

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The plasma concentrations of both immunoreactive erythropoietin (EPO) and lactate were determined in four healthy untrained subjects at sea level and on the 2nd or 3rd day at altitudes (1,300 and 3,500 m). The mean plasma EPO (18.8 ± 1.6 mU/ml at sea level) increased significantly on the 3rd day at 1,300 m (25.5 ± 2.0 mU/ml, p < 0.05) and showed an almost three-fold increase on the 2nd day at 3,500 m (53.5 ± 3.7 mU/ml, p < 0.001). Likewise, the mean plasma lactate at 3,500 m (3.98 ± 0.27 mmol/l) was 3.6 times as high as that at sea level (1.11 ± 0.05 mmol/l) (p < 0.001). The plasma EPO concentrations were found to correlate well with the lactate concentrations at sea level and altitudes (r = 0.86, p < 0.01). These results are consistent with the well-known EPO/lactate response to altitudes and suggest that the circulating EPO concentration as well as blood lactate concentration can be used as an index of anaerobic condition.

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