[Activity of Na, K-ATPase and the enzymes of intermediate metabolism in the brains of rats exposed to electroshock]

Activity of Na, K -ATPase, acetylcholinesterase (AChE) and glutamic acid decarboxylase (GAD) in the fractions of the rat brain and spinal cord tissue were studied in rats during a single electroshock (ES) and 5 and 30 minutes after it. GAD activity of the synaptosome fraction was shown to decrease insignificantly, but activity of AChE, Na, K -ATPase and possibly of proteolytic enzymes increased 5 minutes after electroshock and became normal in 30 minutes. It is supposed that the revealed inhibition of Na, K -ATPase activity in the "synaptosomes" of the rat brain cortex could be of pathogenetic significance in the origination of the convulsive process.

[Acetylcholine induced reciprocal changes in the Na, K-ATPase and acetylcholinesterase activity of nerve and membrane preparations of Na, K-ATF-azy]

ATPase and cholinesterase activities in the homogenate of the frog nerve and membrane Na,K-ATPase preparation of the bovine brain were investigated. Preliminary treatment of the nerve and the preparation by acetylcholine solution (10(-6)--10(-7) M) enhanced their Na,K-ATPase activity and reduced their cholinesterase activity. Possible mechanisms of this phenomenon are discussed.

Elementary steps of the (Na+ + K+)-ATPase mechanism, studied with formycin nucleotides

1. Formycin triphosphate (FTP), a fluorescent analogue of ATP, is a substrate for (Na+ + K+)-ATPase (ATP phosphohydrolase, EC 3.6.1.3), with properties similar to those of ATP. 2. FTP and formycin diphosphate (FDP) bind to the enzyme with high affinity and, on binding, the nucleotide fluorescence is enhanced 3-4-fold. It is therefore possible, with a stopped-flow fluorimeter, to measure the rates of binding and release of FTP and FDP under conditions in which turnover does not occur. 3. When the enzyme-FTP complex is exposed to conditions permitting turnover (Mg2+, Na+ +/- K+), changes in fluorescence occur which can be explained by supposing that they reflect the interconversion of states with or without bound nucleotides. A rapid fall in fluorescence, that we attribute to the rapid release of FDP from newly phosphorylated enzyme, is followed by a steady state in which low fluorescence suggests that little nucleotide is bound. Eventually, exhaustion of FTP allows rebinding of FDP to the enzyme, which is signalled by a rise in fluorescence. 4. The estimated rate of FDP release from newly formed phosphoenzyme is unaffected by the presence of K+ (0-2 mM) or the concentration of FTP (1-20 micron). 5. Experiments with [gamma-32P]FTP show that about 1 mol of 32P is incorporated per mol of enzyme. The rate of phosphorylation of the enzyme by [gamma-32P]FTP has been measured with a rapid-mixing-and-quenching apparatus. 6. Kinetic data from the fluorescence and phosphorylation experiments show that the behaviour of the enzyme, at least at the low nucleotide concentrations employed, is consistent with the Albers-Post model, and is difficult to reconcile with models in which K+ acts at or before the step in which FDP is released during turnover.

Conformational transitions between Na+-bound and K+-bound forms of (Na+ + K+)-ATPase, studied with formycin nucleotides

1. Fluorescence measurements have shown that formycin triphosphate (FTP) or formycin diphosphate (FDP) bound to (Na+ + K+)-ATPase (ATP phosphohydrolase, EC 3.6.1.3) in Na+-containing media can be displaced by the following ions (listed in order of effectiveness): Tl+, K+, Rb+, NH4+, Cs+. 2. The differences between the nucleotide affinities displayed by the enzyme in predominantly Na+ and predominantly K+ media in the absence of phosphorylation, are thought to reflect changes in enzyme conformation. These changes can therefore be monitored by observing the changes in fluorescence that accompany net binding or net release of formycin nucleotides. 3. The transition from a K+-bound form (E2-(K)) to an Na+-bound form (E1-Na) is remarkably slow at low nucleotide concentrations, but is accelerated if the nucleotide concentration is increased. This suggests that the binding of nucleotide to a low-affinity site on E2-(K) accelerates its conversion to E1-Na; it supports the hypothesis that during the normal working of the pump, ATP, acting at a low affinity site, accelerates the conversion of dephosphoenzyme, newly formed by K+-catalysed hydrolysis of E2P, to a form in which it can be phosphorylated in the presence of Na+. 4. The rate of the reverse transformation, E1-Na to E2-(K), varies roughly linearly with the K+ concentration up to the highest concentration at which the rate can be measured (15 mM). Since much lower concentrations of K+ are sufficient to displace the equilibrium to the K-form, we suggest that the sequence of events is: (i) combination of K+ with low affinity (probably internal) binding sites, followed by (ii) spontaneous conversion of the enzyme to a form, E2-(K), containing occluded K+. 5. Mg2+ or oligomycin slows the rate of conversion of E1-Na to E2-(K) but does not significantly affect the rate of conversion of E2-(K) to E1-Na. 6. In the light of these and previous findings, we propose a model for the sodium pump in which conformational changes alternate with trans-phosphorylations, and the inward and outward fluxes of both Na+ and K+ each involve the transfer of a phosphoryl group as well as a change in conformation between E1 and E2 forms of the enzyme or phosphoenzyme.

[Some properties of glial membrane Na, K-ATPase]

Na,K-ATPase activity in glial membranes is rather low that in the nerve ending membranes, but is characterized by the same kind of Na+/K+-dependence. Glial Na,K-ATPase is insensitive to acetylcholine (ACh), 5-hydroxytryptamine (5-HT) and gamma-aminobutyric acid (GABA) while norepinephrine activates Na,K-ATPase at low concentrations and inhibits it at high concentrations. Participation of Na,K-ATPase in the regulatory mechanisms of the neuron-neuroglia relations is discussed.

The program of Friend cell erythroid differentiation: early changes in Na+/K+ ATPase function

Treatment of Friend erythroleukemia cells with several different chemical agents causes an early decrease in the 86Rb+ influx mediated by Na+/K+ adenosine triphosphatase (ATPase). These agents, which induce Friend cells to differentiate, include dimethylsulfoxide (DMSO), ouabain, hypoxanthine, and actinomycin D. The magnitude of the early decrease in 86Rb+ influx correlates with the proportion of cells in cultures of inducible Friend cell clones which later go on to synthesize hemoglobin. Compounds which do not incude differentiation in these cells, such as xanthine, exogenous hematin, and erythropoietin, do not cause a change in 86Rb+ influx. A change in the intracellular K+ ion concentration does not occur during induction by DMSO because, although there is a decrease in K+ content per cell soon after induction, there is a parallel decrease in cell volume. These results and previous observations from this laboratory are discussed in terms of the posible involvement of the Na+/K+ ATPase in Friend cell differentiation.

Potassium adaptation after reduction of nephron population

Two weeks after 75 percent nephrectomy in rats fed a normal diet glomerular filtration rate was found to be reduced by 2/3 and there was no hyperkalemia. Normal K balance was maintained by a threefold increase of fractional urinary potassium excretion. When infused with 0.5 M KCl solution, both normal and 75 percent nephrectomized rats increased their fractional excretion, while normal rats kept on a very high K-diet did not further increase their fractional potassium excretion. Adaptation of fractional excretion to infused KCl was blunted in 75 percent nephrectomized rats given a low K diet.Addition of 0.1 M KCl to the drinking water resulted in a three- to fourfold increase of potassium intake in normal rats: within 7 days, the Na-K-ATPase in the outer medulla of the kidney rose by 30 percent but no change occurred in the cortex. Further increases in dietary K load induced an increase of Na-K-ATPase activity, both in outer medulla and cortex, but not in other tissues. After 75 percent nephrectomy, specific Na-K-ATPase activity increased by 20-25 percent in the outer medulla and in the cortex.Dietary K loading, in normal rats, also resulted in a large increase of net potassium secretion into the perfused colon and of specific Na-K-ATPase activity of the colonic mucosa. These effects of potassium loading were not abolished by adrenalectomy and were accompanied by an increase of transmural PD. It was concluded that chronic potassium loading may enhance secretion of potassium into lower nephron tubular fluid and into colonic contents by primarily stimulating the synthesis of Na-K-ATPase and the resulting increase of the number of pumping sites. 75 percent nephrectomy may induce similar changes in the remaining nephrons.

Na+/K+-dependent adenosinetriphosphatase activity in the skin, kidney and muscle in Xenopus laevis (Daud.) adult specimens under different experimental conditions

Xenopus laevis adult specimens were exposed to environmental changes simulating those undergone by these animals in their natural "habitat". After keeping groups of animals under dry conditions, some of them were returned to water. In both cases some parameters were compared with those of control animals kept in water. A lower activity in the Na+/K+-dependent ATPase of the epidermis and striated muscle was detected in "dry" animals with respect to the control ones or those rehydrated whereas the same ATPase activity in the kidney was higher in "dry" animals than in those from the other groups.

Factors influencing the increase in Na-K-ATPase in compensatory renal hypertrophy

An increase in Na-K-ATPase in kidney homogenates usually accompanies compensatory renal hypertrophy. While it may be evident in both the cortex and medulla of the kidney, it is most marked in the outer medulla and may be present only in that region. The increase in enzyme activity does not depend on an intact adrenal cortex and can be elicited in the absence of adrenal glucocorticoids. It is not seen in the form of renal hypertrophy produced by potassium depletion, in which the transport of sodium and potassium by the kidney is not increased. When present in compensatory renal growth, the enzyme change is correlated with an increase in the reabsorption of sodium, or the excretion of potassium, or both, per unit of renal tissue. It proceeds in the presence of either, but not in the absence of both.

An examination of possible mechanisms of angiotensin II-stimulated steroidogenesis

Dog and rat adrenal glomerulosa cells and subcellular fractions have been utilized to evaluate the mechanism of angiotensin II- and angiotensin III-induced aldosterone production. The effects of angiotensin, ACTH, and potassium have been compared on cyclic AMP and cyclic GMP in isolated glomerulosa cells and adenylate cyclase activity in subcellular fractions. The effect of angiotensin II has also been assessed on Na+-K+-activated ATPase of plasma membrane enriched fractions of dog and rat adrenals. We have demonstrated no effect of angiotensin II or angiotensin III on either adenylate cyclase, cyclic AMP, cyclic GMP, or Na+-K+-dependent ATPase activity over a wide range of concentrations. Potassium ion in concentrations that stimulate significant aldosterone production was also without effect. The negative effects of angiotensin and potassium were contrasted against a positive correlation between an ACTH-induced effect on aldosterone production, adenylate cyclase, and cyclic AMP accumulation. These studies have served to demonstrate that neither adenylate cyclase, cyclic AMP, cyclic GMP, or Na+-K+-activated ATPase seem to be directly involved in the mechanism of action of angiotensins on aldosterone production in the rat and dog adrenal glomerulosa.

Mucosal enzyme patterns in gastric epithelial disease

A correlation was sought between changes in enzymes involved in gastric acid secretion (Mg-, NaK-, K- and HCO3-stimulated ATPases) and histological changes in gastric biopsies. Alkaline phosphatase was also studied. Mg- and NaK-stimulated ATPase activities increased significantly in biopsies from the pylorus and antrum which showed moderate or severe gastritis. NaK ATPase levels increased and HCO3 ATPase decreased in incisural, body and fundic mucosa which had intestinal metaplasia and atrophic gastritis. No K+ ATPase was found in normal mucosa. The total activity of alkaline phosphatase did not vary with histological changes in the gastric mucosa. Results indicate that the ATPase enzyme systems are sensitive indicators of gastric mucosal disease.

Post-obstructive nephropathy in the rat: relationship between NA-K-ATPase activity and renal function

Na-K-ATPase activity and renal function were compared in rats studied after relief of 24 h of unilateral or bilateral ureteral ligation (UUL or BUL), that is, in the absence or presence of post-obstructive diuresis. Na-K-ATPase activity in the outer medulla of the rat kidney after relief of UUL was not significantly altered immediately but was markedly reduced 1 and 3 days post-obstruction. The decrease in medullary Na-K-ATPase activity was not significantly different from that observed after relief of BUL. These results indicate that decreased Na-K-ATPase activity in the post-obstructive kidney is not responsible for post-obstructive diuresis and is not due to uremia, but is a local phenomenon which is probably secondary to altered renal structure or function. It may be due to decreased filtered sodium load or direct tubular damage, but other data suggests that the decreased medullary solute concentration gradient in the post-obstructive kidney (UUL or BUL) may influence Na-K-ATPase activity which, in turn, contributes to the decreased ability to conserve sodium and water.

Variations in (Na+ + K+)-ATPase and Mg2+-ATPase activity of the ground squirrel brain during hibernation

1. The specific activity of brain (Na+ + K+)-ATPase and Mg2+ -ATPase of the ground squirrel (Spermophilus richardsonii) is significantly increased after long-term hibernation. 2. The markedly non-linear thermal dependence of (Na+ + K+)-ATPase is unchanged during hibernation whereas the near linear thermal dependence of Mg2+-ATPase undergoes minor alteration after prolonged hibernation. 3. The sensitivity of (Na+ + K+)-ATPase to inhibition by ouabain is significantly decreased after 100 days of hibernation as is both the rate and amount of [3H]-ouabain binding. 4. These changes may be related to alteration in the phospholipid matrix of the membrane rather than alteration in the protein structure of the enzyme.

Seasonal variations in the renal cortical (Na+ + K+)-ATPase and Mg2+-ATPase of a hibernator, the ground squirrel (Spermophilus richardsonii)

1. The specific activity of renal cortical (Na+ + K+)-ATPase of the Richardson ground squirrel is markedly reduced during hibernation, in contrast to the specific activity of the accompanying Mg2+-ATPase which is markedly increased. 2. The sensitivity of (Na+ + K+)-ATPase to inhibition by ouabain is unchanged by hibernation. 3. Both the non-linear thermal dependence of (Na+ + K+)-ATPase and the linear thermal dependence of Mg2+-ATPase are also unchanged by hibernation. 4. The energy of activation of both enzymes is unchanged during hibernation, or by comparison with that determined in awake controls. 5. There is no evidence for inherent "cold resistance" in these enzyme preparations compared to similar preparations from the non-hibernating rabbit. This parameter does not change during hibernation. 6. Both the rate and amount of specific [3H]-ouabain binding to the renal cortical preparations of (Na+ + K+)-ATPase decrease during hibernation. This decrease matches the fall in enzyme activity so that the ratio of pumping sites/unit of enzyme activity shows no seasonal variations. 7. These findings suggest that the amount of renal cortical (Na+ + K+)-ATPase enzyme falls during hibernation, but that the enzyme which remains functions with the same thermodynamic efficiency and identical biochemical characteristics of that found in the awake summer controls.

Diffusion rates of cell surface antigens of mouse-human heterokaryons. II. Effect of membrane potential on lateral diffusion

The rate of appearance, in a population of mouse-human heterokaryons, of cells with intermixed mouse and human surface antigens may be used to estimate the rate of lateral diffusion of the antigens in a single cell. Most heterokaryons appear to restrict diffusion of their surface antigens. These restrictions are altered by exposing either heterokaryons or their parent cells to conditions that change cell surface membrane potential. Media containing unphysiological concentrations of potassium ion, drugs, affecting the Na+,K+ ATPase, or a channel-forming antibiotic, gramicidin, all affect lateral mobility of cell surface antigens in a manner consistent with a common effect on membrane potential.

Active chloride transport powered by Na-K-ATPase in shark rectal gland

The isolated rectal gland of the spiny dogfish is a unique model for the study of active chloride transport. The gland is stimulated to secrete chloride agains an electrical and a chemical gradient when perfused in vitro by theophylline and/or dibutyryl cyclic AMP. Chloride secretion is depressed by ouabain which inhibits Na-K-ATPase. Thiocyanate and furosemide also inhibit chloride secretion but ethoxolamide, a carbonic anhydrase inhibitor, does not. Chloride transport is highly dependent on sodium concentration in the perfusate. The intracellular concentration of chloride in intact glands exceeds the level expected at electrochemical equilibrium, suggesting active transport of chloride into the cell. These features suggest a general hypothesis for chloride secretion in which the uphill transport of chloride into the cytoplasm is coupled through a membrane carrier to the downhill movement of sodium along its electrochemical gradient. The latter is maintained by the Na-K-ATPase pump while chloride is extruded into the duct by electrical forces.

Structure and function of the Na, K-ion pump or Na, K-ATPase in mammalian kidney

Information about the purified Na, K-ATPase from the mammalian thick ascending limb of Henle is related to studies on its localization in tubular cells and the environment along the transport pathways to reach a better understanding of the role of this pump in the active transtubular transport of Na+.

Immunological characterization of Na+ and K+ mediated structural states of rat kidney Na+-k+-ATPase

As different structural states of the Na+-K+-ATPase (EC 3.6.1.3) may lead to a changed reactivity to antibodies, the influence of different ligands on the reaction between highly purified membrane-bound Na+-K+-ATPase and specific antibodies was investigated. The antigen antibody reaction was registered by measuring the antibody inhibition of Na+-K+-ATPase activity. It was found that Na+ decreased and K+ increased the antibody inhibition of the Na+-K+-ATPase activity of the membrane-bound enzyme if both Mg++ and ATP were present during the antigen antibody reaction. These effects were not observed if ATP was replaced by ADP or by the ATP analog adenylyl (beta-gamma-methylene) diphosphonate. If a solubilized enzyme preparation with the same specific activity was used the effects of Na+ or K+ which were demonstrated in the membrane-bound enzyme could not be detected. The study suggests that the Na+-K+-ATPase structure is altered by Na+ and K+, provided Mg++ and specifically the nucleotide ATP are also present. These structural changes are likely to occur during Na+-K+-transport and do not seem to be necessarily linked to the Na+, K+ and Mg++ stimulated ATP splitting of the enzyme.

Interaction of rumen development and renal gluconeogenesis in lambs

Renal gluconeogenesis of equal aged lambs with different states of rumen development was studied. Going from preruminantto ruminant stage, the rate of glucose formation from several precursors increased. Concomitantly urine pH shifted from acid to base state. Obviously, an enhanced secretion of H+ in lambs kidney during rumen development does not stimulate renal gluconeogenesis. Furthermore, there is no indication from our data that renal gluconeogenesis in lambs is inversely related to the activity of the sodium pump.

Differential lipid control of (Na+ + K+)-ATPase in homeotherms and poikilotherms

1. (Na+ + K+)-ATPase from homeotherms and poikilotherms demonstrate non-linear thermal dependence for ATP hydrolysis. Apparent energies of activation from crab nerve preparations are less than those of brain or kidney preparations from beef, rabbit, sheep or ground squirrel. 2. Crab nerve (Na+ + K+)-ATPase is less sensitive to inhibition by ouabain than that from beef or ground squirrel; lower rates of [3H]-ouabain binding and reduced amount of drug bound at equilibrium are found. 3. K+-activated acyl-phosphatase is similar in all preparations. 4. Fluorescence polarization of 12-AS labelled membranes demonstrate greater mobility of crab nerve lipids compared to beef brain which has a thermal transition at 20-25 degrees C. Crab nerve is linear in this range.

Tissue metabolism and enzyme activities in the rodent Heterocephalus glaber, a poor temperature regulator

1. Tissue oxygen uptake and enzyme activities were investigated in the naked mole rat, Heterocephalus glaber, a mammal notable for its low body temperature and metabolism and poor temperature regulating ability. 2. Q10 for O2 uptake of Heterocephalus crude liver homogenates ranged from 1.91 for the temperature interval 25-30 degrees C to 1.76 within the range 30-38 degrees C, values similar to those reported for typical homoiotherms. 3. Km pyruvate of lactate dehydrogenase in heart muscle had the same temperature dependence in the mole rat and mouse. 4. O2 uptake and cytochrome oxidase activity of skeletal muscle were higher for mole rat than mouse. The reverse was true for heart muscle. Brain and liver O2 uptake showed similar values for both species, while kidney O2 uptake was highest in the mouse. 5. Pyruvate kinase activity in heart and skeletal muscle was higher in mouse than mole rat, suggesting a greater reliance on glycolysis in the former. 6. Na+, K+ -ATPase activity of liver and kidney was 60% higher in mouse than mole rat, while brain was 30% higher in mouse. 7. The results indicate that the effects of temperature on tissue metabolism in the mole rat conform to those in typical homoiotherms. The low body temperature and O2 uptake in the mole rat find no expression in the tissue respiratory capacity.

Rates of ion movement from plasma to endolymph in the dogfish

The rates of movement of Na+, Rb+, Cl- and HCO3- from plasma to endolymph were studied in the elasmobranch fish, Squalus acanthias, by use of the appropriate isotopes. Rb+ was used as a marker for K+. The half-times to equilibrium for Na+, Rb+ and Cl- were about 100 hours; for HCO3- it was 6 hours. The equilibrium ratios, endolymph/plasma, are Na+ 0.87, K+ 26, Cl- 1.37, HCO3- 1.47. Carbonic anhydrase inhibition decreased the rate of HCO3- accumulation, suggesting that the process is actually the formation of endolymphatic HCO3- from plasma or tissue CO2. Increase in plasma pCO2 elevates endolymph HCO3- concentration. The secretory tissue contains carbonic anhydrase and Na-K-ATPase. These and other data suggest that a dominant feature of endolymph chemistry may be HCO3- formation linked in some fashion with K+ transport, through rates catalyzed by these two enzymes.

Cochlear function and sodium and potassium activated adenosine triphosphatase

The maintenance of the cation gradients between endolymph and perilymph in the cochlea requires the operation of a cation pump. An adenosine triphosphatase system activated by sodium and potassium is present in high activity in the cochlear membranes (tegmentum vasculosum and stria vascularis). The cochlear microphonic potential is inhibited by perilymphatic perfusion of ouabain and erythrophleine. Since the microphonic potential depends on the high concentration of potassium ions in the endolymph, our findings strongly suggest the operation of an adenosine triphosphatase cation pump system activated by sodium and potassium, in the generation of cochlear cation gradients.