Relation of ATPases in rat renal brush-border membranes to ATP-driven H+ secretion.

In the presence of inhibitors for mitochondrial H+-ATPase, (Na+ + K+)- and Ca2+-ATPases, and alkaline phosphatase, sealed brush-border membrane vesicles hydrolyse externally added ATP demonstrating the existence of ATPases at the outside of the membrane ("ecto-ATPases"). These ATPases accept several nucleotides, are stimulated by Ca2+ and Mg2+, and are inhibited by N.N'-dicyclohexylcarbodiimide (DCCD), but not by N-ethylmaleimide (NEM). They occur in both brush-border and basolateral membranes. Opening of brush-border membrane vesicles with Triton X-100 exposes ATPases located at the inside (cytosolic side) of the membrane. These detergent-exposed ATPases prefer ATP, are activated by Mg2+ and Mn2+, but not by Ca2+, and are inhibited by DCCD as well as by NEM. They are present in brush-border, but not in basolateral membranes. As measured by an intravesicularly trapped pH indicator. ATP-loaded brush-border membrane vesicles extrude protons by a DCCD- and NEM-sensitive pump. ATP-driven H+ secretion is electrogenic and requires either exit of a permeant anion (Cl-) or entry of a cation, e.g., Na+ via electrogenic Na+/D-glucose and Na+/L-phenylalanine uptake. In the presence of Na+, ATP-driven H+ efflux is stimulated by blocking the Na+/H+ exchanger with amiloride. These data prove the coexistence of Na+-coupled substrate transporters, Na+/H+ exchanger, and an ATP-driven H+ pump in brush-border membrane vesicles. Similar location and inhibitor sensitivity reveal the identity of ATP-driven H+ pumps with (a part of) the DCCD- and NEM- sensitive ATPases at the cytosolic side of the brush-border membrane.

Function and regulation of the avian caecal bulb: influence of dietary NaCl and aldosterone on water and electrolyte fluxes in the hen (Gallus domesticus) perfused in vivo.

The function of the caecal bulb, and its adaptation to chronic high- or low-Na+ intake, was investigated by in vivo perfusion of anaesthetised birds. Effects of acute aldosterone injection (125 micrograms.kg-1 body mass) were also measured. Evidence was found for primary active net absorption of Na+, inducing parallel Na-linked absorption of water and Cl- and secretion of K+. Around 20-35% of total Cl- absorption and K+ secretion were independent of Na+ fluxes, and these components appear to be driven by passive processes with apparent conductances of 6.3 X 10(-3) (GCl) and 1.1 X 10(-3) (GK) S.cm-2. Acetate (40 mM) stimulated Na+ fluxes (8.5-9.9 microEq.cm-2.h-1) and Na-linked water fluxes (27-44 microliters.cm-2.h-1). Increased coupling ratios (2.9-4.6 microliters.microEq-1) and other data indicate that these effects may be due to increased osmotic permeabilities of barriers involved in the Na-linked water transfer pathway. Low-Na+ maintenance enhanced EPD (49-69 mV, serosa positive) and all net fluxes: JNa (6.8-11.6); JK (-3.2--4.3); JCl (4.3-5.6 microEq.cm serosal area-2.h-1); Jv (28-43 microliters.cm-2.h-1) (mucosal-serosal fluxes positive). Acute aldosterone enhanced JNa (10.8-14.0 microEq.cm-2.h-1) and EPD (54-66 mV) by 3 h after injection, but had no effect on the Na-linked components of JK or JCl.

The role of dietary electrolytes in hypertension.

The possible contribution of dietary electrolyte intake as a cause of or contributor to the development of hypertension has been intensively investigated for over 50 years. Evidence from various sources suggests a role for sodium-salt, chloride, calcium, and magnesium. In this article, we will review the evidence supporting a role for each of these electrolytes in human hypertension.

Cellular concentration of magnesium and other ions in relation to protein synthesis, cell proliferation and cancer.

This report concerns the possible regulatory roles of intracellular Mg, Na, K, Cl, H and Ca ions in protein synthesis, mitogenesis and oncogenesis. Our main approach was to measure the intracellular concentration of various ions in different mammalian tissue cell populations for correlation with the rate of protein synthesis, the rate of cell proliferation and the tumorigenic cell state. Mg concentration alone showed a significant positive correlation to protein synthetic rate, suggesting a key role for Mg in regulation of protein synthesis. All ions measured (Mg, Na, K, Cl) showed a significant positive correlation to the rate of cell proliferation in normal populations of tissue cells. Likewise rapidly dividing tumor cells showed markedly elevated concentrations of Na and Cl but not Mg and K. The tumor cells are therefore unique in terms of their ionic composition. The injection of tumorous mice with amiloride (a drug which blocks the passive influx of Na into cells and blocks the Na-H antiport process) lowered intracellular Na concentration without significantly changing the concentration of Mg or K in the rapidly dividing tumor cells. The cell proliferation rates of both normal and of tumor cell populations were decreased by this amiloride treatment. These data strongly suggest a regulatory role for Na and H concentration on the rate of cell proliferation in both normal and tumor cells. Recent reports have shown that a brief surge in free Ca occurs after mitogenic stimulation and at several other key points in the cell cycle. These findings suggest a signaling role for free Ca in cells. A model of the temporal sequence of ionic events in the cell cycle is presented. The report ends with a brief discussion of the role of ions in tumorigenic cell transformation.

Regional pH and electrolyte homeostasis of cat brain after prolonged ischemia.

Following prolonged cerebral ischemia, primary electrophysiological recovery may be followed by secondary deterioration of the recovery process. It has been suggested that the secondary deterioration is caused by "late" cytotoxic brain edema. To test this hypothesis, adult normothermic cats were submitted to 1 h complete cerebral ischemia followed by 3 and 6 h recirculation, respectively. Postischemic recovery of energy metabolism was imaged by ATP-induced bioluminescence, and regional tissue pH and electrolyte content was measured in regions with and without metabolic recovery. In areas with postischemic restitution of metabolic activity, sodium gradually rose from 338 +/- 17 to 488 +/- 28 mumol/g protein and calcium from 8.81 +/- 0.35 to 18.24 +/- 0.97 mumol/g protein. Tissue potassium content decreased from 761 +/- 12 to 676 +/- 19 mumol/g protein and magnesium from 46.8 +/- 0.8 to 36.3 +/- 1.1 mumol/g protein. Tissue pH rose from 7.09 +/- 0.04 to 7.31 +/- 0.13 and 7.26 +/- 0.17 after 3 and 6 h recirculation, respectively. In areas without metabolic recovery, electrolyte disturbances were even more pronounced and pH--after transient alkalization--fell to 6.82 +/- 0.12. These data demonstrate that during the later phase of postischemic recirculation, progressive disturbances of electrolyte homeostasis create a preedematous situation that has to be considered for preventing delayed postischemic complications.

Perinatal fluid and electrolyte regulation: role of arginine vasopressin.

Not many years ago, the fetus was perceived to exert little impact on amniotic fluid homeostasis. It is now clear that the fetus plays an integral role in modulating fluid flux between the maternal, fetal, and amniotic fluid compartments. Moreover, fetal AVP secretion and the associated renal and cardiovascular responses represent important aspects of the potential to adapt to changes in the intrauterine environment. Although the physiologic significance of the increased AVP secretion observed in response to labor and delivery remain speculative, AVP regulation also is an essential aspect of neonatal adaptation. Still, many questions remain regarding both the regulation of fetal and neonatal fluid dynamics and the ontogeny of AVP receptor systems.

An analysis of the delayed outward current in single ventricular cells of the guinea-pig.

Properties of the delayed outward current (IK) in ventricular myocytes of the guinea-pig were studied using the whole cell clamp method. The experiments were performed under conditions in which IK was enhanced by application of isoproterenol while the Ca2+ current was eliminated by Ca2+-removal and by the addition of Cd2+. The reversal potential (Erev) of IK, determined from the current tails, was about 10 mV less negative than the K+ equilibrium potential. This was estimated by examining the reversal potential of the inward rectifier K+ current in Ba2+-containing solution, or from the Nernst equation. The Erev--log[K+]o relationship had a slope of 49 mV per tenfold change in [K+]o. In Na+-free solution, Erev became more negative. Thus, although the major charge carriers in IK are K+ ions, Na+ ions may also contribute in part to this current. The PNa/PK ratio in IK, calculated by applying a Goldman-Hodgkin-Katz relation to the reversal potential, was 0.016. The activation of IK during depolarization showed a sigmoidal time course at the onset, while the time course of the current tails was monoexponential at voltages more negative than-50 mV, but biexponential at more positive voltages. These observations can be explained by the conductance equation of the Hodgkin-Huxley type in which the kinetic variable is raised to the second power. These and other features of IK observed in the ventricular cells are discussed in comparison to the properties of similar current systems reported in other cardiac preparations.

Contribution of salt to arterial wall changes in DOCA hypertension in the rat.

The contribution of drinking fluid salt to the development of deoxycorticosterone (DOCA) hypertension and arterial wall changes was assessed in unilaterally nephrectomized rats. Half of the DOCA-treated animals received saline supplemented with 0.2% KCl and the other half received deionized water as drinking fluid. All animals were fed standard rat chow (Na content = 0.36%). After 8 weeks, arterial pressures were significantly elevated in both DOCA groups to values which were not significantly different. The heart weight to body weight ratio was also elevated in both DOCA groups with a larger response in the saline-treated ones. Body weight of saline-treated DOCA rats was significantly lower than untreated controls and water-treated DOCA rats. Arteries from both DOCA groups exhibited increased passive stiffness, larger maximum active stress, wall thickening, decreased collagen and elastin concentration, greater relative cell volume, and greater water and cation concentrations. Larger changes were generally found in the saline- than the water-treated group. These results show that saline administration is not necessary for the development of hypertension or hypertension-induced arterial wall changes in DOCA-treated, uninephrectomized rats. Hypertension developed more slowly and arterial wall changes were similar in magnitude in water-treated animals. These results suggest that the rate and/or time history of pressure elevation may be an important factor contributing to hypertension-related arterial changes.

Magnesium and hypertension.

Essential hypertension (EHT) is one of the most common risk factors for cerebrovascular and cardiovascular disease (CVD), which in turn are among the most common causes of death and disability in developed countries. Drug treatment of EHT has proven effective in lessening the risk of CVD, but has attendant risk of side effects, some of which are of risk to the CV system. Thus, increasing attention is being paid to non-drug treatment of EHT, which includes changing the daily intake of such electrolytes as sodium (Na), potassium (K), calcium (Ca), and magnesium (Mg). Decreasing Na intake to control blood pressure (BP) is well established. On the basis of epidemiologic and experimental studies, increasing K and/or Mg intakes, and increasing of decreasing Ca intakes, have each been proposed to have beneficial effects of BP. Presented here is a review of the background data supporting the rationale for adding Mg to the anti-hypertensive regimen. There is evidence that Mg can exert a favorable effect in EHT, particularly when used in combination with K during diuretic therapy.

Spreading depression in the olfactory bulb of rats: reliable initiation and boundaries of propagation.

Spreading depression in the olfactory bulb of rats is an elusive phenomenon, the demonstration of which requires specific conditioning procedures. The present paper describes a simple technique for reliable initiation of bulbar spreading depression with microinjections of potassium acetate. Adult hooded rats were anesthetized with pentobarbital (50 mg/kg) and slow potential changes accompanying spreading depression were recorded with capillary microelectrodes stereotaxically inserted into the olfactory bulb and adjacent forebrain structures. KCl microinjection (0.5-1.0 microliter, 0.134-0.670 mol/l) into the olfactory bulb elicited local depolarization which only exceptionally developed into a propagating spreading depression. Potassium acetate (0.5-1.0 microliter, 0.15 mol/l) injected into the rostral olfactory bulb evoked a negative slow potential wave (amplitude of around 25 mV and duration 30-50 s) propagating at a rate of 3-4 mm/min through all the olfactory bulb layers. Low positive (5 mV) instead of negative waves were recorded in the superficial olfactory nerve layer with reversal in the glomerular layer (200-300 micron). The slow potential decreased in the rostrocaudal direction and expired at the caudal boundary of the olfactory bulb. Bulbar spreading depression never spread to neocortex, and cortical spreading depression never entered into the olfactory bulb but stopped in the anterior olfactory nucleus 7 mm rostral to bregma. Repeated potassium acetate injections into the olfactory bulb occasionally elicited a series of spreading depression waves recurring at regular intervals, probably reflecting reverberation of scroll-shaped waves around the rostrocaudal axis of the olfactory bulb.(ABSTRACT TRUNCATED AT 250 WORDS)

Molecular kinetic modelling of associative learning.

Three molecular (enzyme) kinetic models have been designed that exhibit the basic properties of associative learning (classical conditioning). The enzyme systems are acted upon by an 'unconditioned' and a 'conditioned' ligand: temporally paired application of the two ligands leads to covalent enzyme modification, which serves as 'memory trace'. The behaviour of the systems has been investigated by computer simulation. Although the models are hypothetic, they do not contain biochemically inconceivable steps. The models demonstrate that already fairly simple molecular events may produce the phenomenology of associative learning.

Cartilage electromechanics--I. Electrokinetic transduction and the effects of electrolyte pH and ionic strength.

Articular cartilage contains a high fixed charge density under physiological conditions associated primarily with the ionized proteoglycan molecules of the extracellular matrix. Oscillatory compression of cartilage using physiological loads produces electrical potentials that have been shown previously to be the result of an electrokinetic (streaming) transduction mechanism. We have now observed two additional electromechanical phenomena not previously seen in cartilage or other soft tissues: 'streaming current' and 'current-generated stress'. Sinusoidal mechanical compression induced a sinusoidal streaming current density through cartilage disks when the Ag/AgCl electrodes that were used to compress the cartilage were shorted together externally. Conversely, a sinusoidal current density applied to the tissue generated a sinusoidal mechanical stress within the tissue. Both these phenomena were found to be consistent with the same electrokinetic transduction mechanism responsible for the streaming potential. Changes in the measured streaming potential response that resulted from modification of bath ionic strength and pH have provided additional insights into the molecular origins of these transduction processes. Finally, we have now observed streaming potentials in living cartilage maintained in organ culture, as well as in previously frozen tissue.

Influence of cation markers on sulfate distribution in mouse gastrocnemius muscle.

Further studies are reported which examines the influence of fixed negative sites on anion distribution in the interstitium of mouse gastrocnemius muscle. For this purpose, the 35S-sulfate distribution in in vitro muscles was examined in the absence and presence of a number of cations which are thought to bind to the interstitial fixed negative sites. Each of the cation treated muscles gave sulfate space measurements which were statistically greater than the control muscles. Ferritin, spermidine and ruthenium red treatment resulted in muscle sulfate spaces similar to the true morphometric ECV. This study suggests that the fixed negative sites in the interstitium of mouse gastrocnemius muscle exists in sufficient density to influence the distribution of anions in these tissue.

Hormone-electrolyte interactions in the pathogenesis of lethal cardiac arrhythmias in patients with congestive heart failure. Basis of a new physiologic approach to control of arrhythmia.

Congestive heart failure is the most arrhythmogenic disorder in cardiovascular medicine. As left ventricular performance deteriorates and symptoms of dyspnea and fatigue become progressively more severe, nearly all patients with heart failure experience frequent and complex ventricular tachyarrhythmias and nearly half die suddenly during long-term follow-up. This imminent risk of sudden death appears to be present for all patients with congestive heart failure; ambulatory electrocardiographic monitoring and programmed electrical stimulation are not useful in distinguishing patient subsets that are particularly predisposed to fatal arrhythmic events. Although conventional antiarrhythmic agents are widely prescribed as a nonspecific approach to prevent sudden death in these patients, there is little evidence to indicate that these drugs possess clinically important antiarrhythmic activity in patients with congestive heart failure, and these agents frequently serve to exacerbate the heart failure state and the underlying ventricular tachyarrhythmia. A useful approach to the prevention of sudden death in patients with congestive heart failure addresses the reversible causes of lethal ventricular arrhythmias in these individuals. Both experimental and clinical evidence indicates that circulating neurohormones and electrolyte deficits (particularly of potassium and magnesium) interact to provoke malignant ventricular ectopic rhythms and that the prevention of electrolyte depletion and the use of neurohormonal antagonists may exert clinically important antiarrhythmic actions. This physiologic approach may prove to be a more effective means of ameliorating the problem of sudden death than the empiric administration of conventional antiarrhythmic drugs.

[Current data on insulin secretion and its regulation]. / Données actuelles sur l'insulino-sécrétion et sa régulation.

Glucose is the main stimulator and physiological regulator of insulin secretion. The great sensitivity of the B cell to glucose variations between 1 g/l (5.5 mM) and 3 g/l (16.6 mM) and its rapid response ensure the constant adaptation of its secretion to plasma glucose level. The cellular mechanisms involved in insulin response can be schematically represented in three stages: The first stage is the recognition of the insulinotropic agent. In the case of glucose, this involves its metabolism. The second one is the coupling of the recognition process to activation of the effector system and implies a series of intracellular signals. Coupling factors include metabolites and cofactors, ions, cyclic AMP, polyphosphoinositides. The result of all these cellular events is the increase in cytosolic Ca2+ and the activation of protein-kinases: Ca2+-calmodulin-, cAMP- and Ca2+-phospholipid-dependent protein kinases. The last stage corresponds to a mechanical one, involving granule migration and extrusion. The polymerization of microtubules associated with contraction of microfilaments would cause granule movement. Ca2+-calmodulin-dependent protein kinases would play a major role. While glucose is the main stimulator of insulin secretion, numerous factors can influence it. The regulation of this secretion is essentially under the control of three classes of elements: nutrients, hormones and neurotransmitters. As to stimulation of insulin secretion by nutrients, it seems to be secondary to an increase in intracellular metabolism. However it must be underlined that the insulin secretory effect of most nutrients requires the presence of glucose which is consequently a permissive factor. A number of gastrointestinal and pancreatic hormones stimulate, in presence of glucose, insulin secretion and play an essential role during food intake, which results in a better fitting of insulin secretion to energy supply. The term "incretin" designates a hormonal transmitter between the gastrointestinal tract and the B cell; the "incretin" factors are included in what is termed enteroinsular axis. Of the gastrointestinal hormones, GIP (gastric inhibitory polypeptide) appears to play the most important physiological role in potentiating the insulin secretory effect of glucose. Pancreatic glucagon potentiates the effect of glucose too; it is difficult to distinguish between its endocrine and paracrine role. The pancreatic B cell is under neural regulation. The cholinergic system stimulates insulin secretion and the B cell is fitted with receptors of muscarinic type.(ABSTRACT TRUNCATED AT 400 WORDS)