Reversal of net secretion to net absorption of potassium in rat large intestine by dietary potassium depletion

Feeding rats a diet low in potassium and high in sodium for 2 weeks led to a reversal of net potassium secretion to net potassium absorption in ligated segments of distal large intestine (colon descendens and rectum) under in-vivo conditions. This change in the direction of net potassium transport is probably important for the maintenance of potassium homeostasis.     

High potassium intake increases the plasma concentration and urinary excretion of vasopressin in the rat

Summary The effect of alterations of dietary potassium intake on the plasma concentration and the urinary excretion of vasopressin was studied in male rats. Ingestion of a high potassium diet resulted in increases in the plasma concentrations of potassium and vasopressin, systolic blood pressure, urine flow, and urinary vasopressin excretion. Ingestion of a low potassium diet had little effect on the plasma vasopressin concentration and systolic blood pressure but caused decreases in the plasma potassium concentration and urinary vasopressin excretion. The results indicate that physiological changes in the plasma potassium concentration or some other consequence of altered dietary potassium intake can affect vasopressin release and excretion.     

Evidence of abnormalities in net sodium and potassium fluxes in erythrocytes of patients with essential hypertension]

A new and simple laboratory test for measuring net Na+ and K+ fluxes in Na+-loaded/K+-depleted human erythrocytes was developed and applied to hypertension. Moderate essential hypertension was characterized by a constant increase in net K+ influx; more severe cases showed a drop in net Na+ efflux. Na+ and K+ erythrocyte fluxes were found to be normal in hypertension of renal origin.     

Inhibition of potassium (86Rb) influx in Ehrlich ascites cells by bilirubin and ouabain

Summary Bilirubin inhibited influx of potassium into Ehrlich ascites cells without altering efflux. The data showed that compared with ouabain, net potassium influx components were impaired in a higher degree by bilirubin. The reversal of this effect was shown, in our experimental conditions, only for ouabain.Acknowledgments. This work was supported by a grant from the Consejo Nacional de Investigaciones Cientificas y Técnicas, República Argentina. The authors wish to thank Miss Marta S. Göthje for techical assistance.     

Proton and potassium fluxes in rat red blood cells incubated with sugar phosphates

Summary Fructose-1,6-diphosphate counteracts potassium ejection and proton uptake induced in rat red blood cells by valinomycin and an uncoupler. The effect on potassium ejection is reduced in the presence of ouabain and divalent cations.     

The effect of a phorbol ester upon the cholinergic regulation of potassium permeability in the rat submandibular gland

Acetylcholine releases calcium from cytoplasmic stores and permits an influx of calcium in salivary acinar cells. The resultant rise in [Ca²⁺]_i causes an increase in potassium permeability which is an important part of the secretory response. We have investigated the effects of 12-0-tetradecanoyl phorbol-13-acetate, a potent activator of protein kinase C, upon this regulation of potassium permeability in superfused pieces of rat submandibular salivary gland. This compound inhibited the initial [Ca²⁺]_o-independent component of the response of acetylcholine but had no effect upon the subsequent [Ca²⁺]_o-dependent phase. This compound does not, therefore, appear to inhibit receptor-regulated calcium influx.     

Forecast intervals of net migration: the case of the Netherlands

This study addresses problems concerning the forecasting of net migration in the preparation of population forecasts. "As the width of forecast intervals for migration in single years differs strongly from that of an interval for average migration during the forecast period, it is important that the forecaster indicates which type of interval is presented. A comparison of forecast intervals for net migration obtained from an ARIMA model to intervals in official Dutch national population forecasts shows that the uncertainty on migration has been underestimated in past official forecasts."     

Peptide YY enhances NaCl and water absorption in the rat colon in vivo

Peptide YY (PYY) is thought to possess paracrine and endocrine functions. The highest concentrations of this peptide are in the colonic mucosa. The effect of PYY on electrolyte and water transport in the rat colon was studied in vivo. Under urethane anesthesia, rat colonic loops were perfused at a constant rate with physiological buffer solution containing phenol red as a nonabsorbable volume marker, and net movements of water, sodium, chloride and potassium in the perfused colon were determined every 10 min. Intravenous administration of PYY produced a dose-dependent increase in the net absorption of sodium chloride and water, as well as a decrease in the net secretion of potassium. PYY inhibited the reduction in net absorption of sodium chloride and water evoked by vasoactive intestinal peptide (VIP), but did not affect the VIP-evoked increase in net potassium secretion.These findings suggest that PYY acts as an enhancer of sodium chloride and water absorption and as an antagonist to VIP-induced secretion in the colon.     

Peptide YY enhances NaCl and water absorption in the rat colon in vivo.

Peptide YY (PYY) is thought to possess paracrine and endocrine functions. The highest concentrations of this peptide are in the colonic mucosa. The effect of PYY on electrolyte and water transport in the rat colon was studied in vivo. Under urethane anesthesia, rat colonic loops were perfused at a constant rate with physiological buffer solution containing phenol red as a nonabsorbable volume marker, and net movements of water, sodium, chloride and potassium in the perfused colon were determined every 10 min. Intravenous administration of PYY produced a dose-dependent increase in the net absorption of sodium chloride and water, as well as a decrease in the net secretion of potassium. PYY inhibited the reduction in net absorption of sodium chloride and water evoked by vasoactive intestinal peptide (VIP), but did not affect the VIP-evoked increase in net potassium secretion. These findings suggest that PYY acts as an enhancer of sodium chloride and water absorption and as an antagonist to VIP-induced secretion in the colon.     

Self-association of 5'-GMP: nucelation by potassium ions]

23Na and 39K nuclear magnetic resonance are used to follow the self-assocation of 5'-GMP in aqueous solutions. For a 0,1 M concentration in 5'-GMP, large aggregates are formed only in presence of the potassium ion, at greater than 0.2 M concentrations. They do not appear with the other alkali metal cations. A plausible explantation is inclusion of the cation in the central cavity of 5'-GMP tetramers, with a marked selectivity in favor of potassium.     

Inhibitory effect of some heteropolyanions on potato virus X

Summary Heteropolyanions like 12-tungstozincic acid (i.i.), potassium 13-vanadomanganate (i.v.), potassium 13-vanadonickelate (i.v.) and sodium tungstoborate produced an inhibitory effect on potato virus X. Amongst these, tungstozincic acid was found to be the most potent.The authors are thankful to Prof. R. P. Rastogi, Head of the Chemistry Department, University of Gorakhpur for providing necessary facilities. The financial support by Council of Science and Technology, U.P., Lucknow is gratefully acknowledged.     

High potassium intake increases the plasma concentration and urinary excretion of vasopressin in the rat

The effect of alterations of dietary potassium intake on the plasma concentration and the urinary excretion of vasopressin was studied in male rats. Ingestion of a high potassium diet resulted in increases in the plasma concentrations of potassium and vasopressin, systolic blood pressure, urine flow, and urinary vasopressin excretion. Ingestion of a low potassium diet had little effect on the plasma vasopressin concentration and systolic blood pressure but caused decreases in the plasma potassium concentration and urinary vasopressin excretion. The results indicate that physiological changes in the plasma potassium concentration or some other consequence of altered dietary potassium intake can affect vasopressin release and excretion.     

Molecular and cellular basis of small- and intermediate-conductance, calcium-activated potassium channel function in the brain

Small conductance calcium-activated potassium (SK or K_Ca2) channels link intracellular calcium transients to membrane potential changes. SK channel subtypes present different pharmacology and distribution in the nervous system. The selective blocker apamin, SK enhancers and mice lacking specific SK channel subunits have revealed multifaceted functions of these channels in neurons, glia and cerebral blood vessels. SK channels regulate neuronal firing by contributing to the afterhyperpolarization following action potentials and mediating I_AHP, and partake in a calcium-mediated feedback loop with NMDA receptors, controlling the threshold for induction of hippocampal long-term potentiation. The function of distinct SK channel subtypes in different neurons often results from their specific coupling to different calcium sources. The prominent role of SK channels in the modulation of excitability and synaptic function of limbic, dopaminergic and cerebellar neurons hints at their possible involvement in neuronal dysfunction, either as part of the causal mechanism or as potential therapeutic targets. Received 23 April 2008; received after revision 29 May 2008; accepted 4 June 2008     

Effect of hyperkalemia on insulin secretion

Summary The effect of hyperkalemia on insulin secretion remains undefined. We evaluated portal and peripheral insulin levels in anesthetized dogs after infusions of KCl. The mean maximal increase in peripheral plasma potassium at infusion rates of 0.2 mEq/kg/h was 0.68±0.20 mEq/l. There were no significant increases in either portal or peripheral insulin levels. In contrast, in six dogs whose plasma potassium concentration increased in each case by more than 2.0 mEq/l (infusion rate of 0.5 mEq/kg/h), portal insulin levels increased fivefold (p<0.05). We conclude that only marked increases in plasma potassium concentration stimulate pancreatic insulin secretion.     

Proton and potassium fluxes in rat red blood cells incubated with sugar phosphates

Fructose-1,6-diphosphate counteracts potassium ejection and proton uptake induced in rat red blood cells by valinomycin and an uncoupler. The effect on potassium ejection is reduced in the presence of ouabain and divalent cations.     

Adenosine activates a potassium conductance in guinea-pig atrial heart muscle

Adenosine shortens the action potential and diminishes the force of contraction in guinea-pig left atria. These effects may be brought about by the activation of a potassium conductance. This assumption is supported by voltage clamp and 42K release experiments.     

The potassium concentration of frog Ringer's solution

Résumé Pour être certain que le dégagement et l'absorption du potassium sont exactement compensés dans un muscle de grenouille étudiéin vitro dans la solution de Ringer, il faut adapter la concentration du potassium de cette solution aux conditions particulières de l'expérience et tenir compte du fait que le degré de concentration requis varie d'un muscle à l'autre.

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This investigation was supported by PHS grant no. A-4718 from the National Institute of Arthritis and Metabolic Diseases, U.S. Public Health Service.     

Die Wirkung von Herzglykosiden und Kalzium auf den Kaliumtransport im Herzmuskel

Summary In isolated perfused guinea pig hearts, both strophanthin and calcium produced positive inotropic effects and contracture increasing with the concentration of the drugs. Strophanthin caused a net loss of potassium from the heart to the perfusing fluid whereas calcium did not interfer in the same way with potassium exchange. The data are consistent with the view that the positive inotropic effect of cardiac glycosides depends mainly on the increased intracellular calcium concentration, perhaps due to inhibition of the active potassium and sodium transport.     

Red blood cell glycolysis and potassium type in sheep

Summary Based on the observations made on human and dog red blood cells, it was recently proposed that the response of red cell glycolysis to variations in the levels of specific cations is an evolutionary adaptation in response to a specific cellular environment. We have now examined the effect of K⁺ and Na⁺ on the activity of pyruvate kinase (PK) in the red blood cells from 2 genetically different types of sheep high potassium (HK) and low potassium (LK). The results indicate that K⁺ stimulate glucose consumption and the activity of PK in both types of sheep. It thus appears that red cell PK from LK sheep does not fit into the concept of cellular environment and PK activity.This work was supported by grants from the National Health and Medical Research Council of Australia, the Clive and Vera Ramaciotti New South Wales Foundation and the Helena Rubenstein Foundation, Inc.     

Spectral properties of methemoglobins prepared by the action of sodium nitrite and potassium ferricyanide

Summary Methemoglobin was prepared by the addition of sodium nitrite or potassium ferricyanide to oxy or deoxyhemoglobin. The spectral properties of these methemoglobins were studied before and after extensive dialysis. It is shown that the methemoglobin formed by sodium nitrite has substantial spectral differences in visible and Soret band compared to that formed by potassium ferricyanide. These differences are proportional to the excess of sodium nitrite only. This suggests that both methemoglobins are similar compounds.Supported by NIH grant No. 5R01AM 20181-03 and VA grant No. 5455-003.Acknowledgments. The technical assistance of Ms Carol A. Perry and the secretarial assistance of Ms Wanda Stewart are highly appreciated.