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PubMed2003

Effects of potassium deficiency on potassium, polyamines and amino acids in mouse tissues.

Sexual dimorphism in potassium content was found in plasma, kidney, heart and skeletal muscle of CD1 mice. We observed that feeding mice with a K(+)-deficient diet had an uneven and gender-dependent effect on organ weight and tissue potassium concentrations. Treatment produced a marked decrease in plasma, pancreas and skeletal muscle K(+) levels in both sexes, and a reduction in kidney, liver and heart potassium concentrations in females. Moreover, K(+) deficiency produced a 2-3-fold increase in the concentrations of cationic amino acids, such as arginine and lysine in both heart and skeletal muscle of the two sexes, a slight increase ( approximately 37%) in renal arginine in the male mice. The concentrations of these amino acids in plasma and other tissues in both sexes remained unaltered. Polyamine levels in heart, liver, skeletal muscle and pancreas from male and female mice were not affected by K(+) deficiency. However, in the male kidney potassium deficiency was accompanied by an increase of putrescine and spermidine concentration, and a reduction of putrescine excretion into the urine, even though renal K(+) concentration was not significantly affected and ornithine decarboxylase activity was dramatically decreased. The general lack of correlation between tissue potassium decrease and the increase in organic cations suggests that it is unlikely that the changes observed could be related with an attempt of the tissues to compensate for the reduction in cellular positive charge produced by the fall in K(+) content. The mechanisms by which these changes are produced are discussed, but their physiological implications remain to be determined.

Amino Acids↗
PubMed1984

Potassium supplements or potassium-sparing agents.

During diuretic treatment alterations in myocardial cellular excitability due to potassium-induced disturbances of the membrane potential may arise without obvious changes of total body K. This may be explained by coexisting disturbances of the acid/base balance and other ions such as magnesium, two factors which independently influence the transport of potassium across the cell membrane. The consequence may be cardiac arrhythmias, particularly in the presence of digitalis. On the other hand hypokalemia, induced by diuretics, may also be accompanied by a significant depletion of total body K, bringing about more general consequences. It must be considered essential to maintain a normal general electrolyte balance during diuretic therapy. Potassium supplements may be used if true depletion of total body K is suspected, e.g. in hypokalemia with acidosis. Its use may, however, otherwise be questioned, as it is only directed towards the potassium situation and neglects the influence of diuretics upon other ions, such as H+ and Mg++. The potassium-sparing agents amiloride and triamterene normalize the general electrolyte situation in the distal tubules and should thus be regarded as drugs of first choice. Spironolactone has identical properties concerning the electrolytes but more serious side effects. It should be preferred when a significant secondary hyperaldosteronism is suspected and/or a more intense diuresis or an accentuated antihypertensive action is desired. The role of captopril in this context has not yet been established.

Aldosterone↗
PubMedDate not supplied

Recent advances in the field of renal potassium excretion: what can we learn from potassium channels?

Potassium channels in the apical and basolateral membranes of tubule cells serve several important functions. They contribute to the generation of the cell-negative potential, mediate volume reductions following cell swelling and play a key role in secretion of potassium in both the thick ascending limb of Henle's loop and principal tubule cells of the initial and cortical collecting tubules. Secretion of potassium occurs via a well-defined class of potassium channels distinguished by their low single channel conductance, mild inward rectification, high sensitivity to inhibition by low pH, millimolar concentrations of ATP, arachidonic acid and PKC, and stimulation by vasopressin and pretreatment with a high potassium diet. Genes encoding several isoforms of this channel have been cloned and the proteins located to the apical membranes of cells lining the thick ascending limb of Henle's loop and the collecting tubules, and progress made concerning their structure-function relationship.

Animals↗
PubMed1968

Interaction Between Potassium and Calcium in Their Absorption by Intact Barley Plants. II. Effects of Calcium and Potassium Concentration on Potassium Absorption.

Rates of K absorption by young barley plants grown for 20 days in flowing nutrient solutions have been studied at 3 solution K concentrations (20, 200, and 2000 mum) and at 2 Ca concentrations (250 and 2500 mum). Increasing solution K increased plant K content, concentration, and rate of absorption: solution Ca concentrations had no effect at any K level.Rates of K absorption were only one-half to one-fifth of those reported for excised barley roots at similar K concentrations in solution. If the reported rates of K absorption by the high-affinity mechanism in excised barley roots were maintained in growing plants they would have given, within 3 days, the equilibrium concentrations of K in plants of the present experiment. Thereafter the rates of K absorption by the high-affinity mechanism would have been more than adequate to maintain plant K and would need to have been compensated by K efflux.It is suggested that, for all concentrations of K in solution, the high-affinity mechanism dominates the absorption of K by barley plants grown for more than a few days.

Journal Article↗
PubMed1970

Potassium Fluxes during Potassium Absorption by Intact Barley Plants of Increasing Potassium Content.

The presence of previously absorbed K in plants caused a marked reduction in the short term influx of (86)Rb-labeled K into roots of barley seedlings. The influx values agreed with net K absorption rates into intact plants, thus suggesting that K efflux was negligible in comparison with influx.Earlier interpretations of a large K efflux component from excised roots approaching equilibrium K concentrations are considered to be due to an underestimation of net K absorption rates resulting from xylem exudation as the K status of the roots increased.

Journal Article↗
PubMed1997

Evidence for the existence of a sulfonylurea-receptor-like protein in plants: modulation of stomatal movements and guard cell potassium channels by sulfonylureas and potassium channel openers.

Limitation of water loss and control of gas exchange is accomplished in plant leaves via stomatal guard cells. Stomata open in response to light when an increase in guard cell turgor is triggered by ions and water influx across the plasma membrane. Recent evidence demonstrating the existence of ATP-binding cassette proteins in plants led us to analyze the effect of compounds known for their ability to modulate ATP-sensitive potassium channels (K-ATP) in animal cells. By using epidermal strip bioassays and whole-cell patch-clamp experiments with Vicia faba guard cell protoplasts, we describe a pharmacological profile that is specific for the outward K+ channel and very similar to the one described for ATP-sensitive potassium channels in mammalian cells. Tolbutamide and glibenclamide induced stomatal opening in bioassays and in patch-clamp experiments, a specific inhibition of the outward K+ channel by these compounds was observed. Conversely, application of potassium channel openers such as cromakalim or RP49356 triggered stomatal closure. An apparent competition between sulfonylureas and potassium channel openers occurred in bioassays, and outward potassium currents, previously inhibited by glibenclamide, were partially recovered after application of cromakalim. By using an expressed sequence tag clone from an Arabidopsis thaliana homologue of the sulfonylurea receptor, a 7-kb transcript was detected by Northern blot analysis in guard cells and other tissues. Beside the molecular evidence recently obtained for the expression of ATP-binding cassette protein transcripts in plants, these results give pharmacological support to the presence of a sulfonylurea-receptor-like protein in the guard-cell plasma membrane tightly involved in the outward potassium channel regulation during stomatal movements.

Journal Article↗
PubMed1981

Activation-inactivation of potassium channels and development of the potassium-channel spike in internally perfused squid giant axons.

A spike that is the result of calcium permeability through potassium channels was separated from the action potential is squid giant axons internally perfused with a 30 mM NaF solution and bathed in a 100 mM CaCl2 solution by blocking sodium channels with tetrodotoxin. Currents through potassium channels were studied under voltage clamp. The records showed a clear voltage-dependent inactivation of the currents. The inactivation was composed of at least two components; one relatively fast, having a time constant of 20--30 ms, and the other very slow, having a time constant of 5--10 s. Voltage clamp was carried out with a variety of salt compositions in both the internal and external solutions. A similar voltage-dependent inactivation, also composed of the two components, was recognized in all the current through potassium channels. Although the direction and intensity of current strongly depended on the salt composition of the solutions, the time-courses of these currents at corresponding voltages were very similar. These results strongly suggest that the inactivation of the currents in attributable to an essential, dynamic property of potassium channels themselves. Thus, the generation of a potassium-channel spike can be understood as an event that occurs when the equilibrium potential across the potassium channel becomes positive.

Action Potentials↗
PubMed1990

Effects of central bolus injections of potassium chloride on arterial potassium concentration in patients undergoing cardiopulmonary bypass.

The effects of central venous bolus injections of potassium chloride (KCl) on arterial potassium concentration were studied in patients undergoing cardiopulmonary bypass. Ten subjects were studied, and each received a rapid bolus injection of KCl, 33 microEq/kg, both before and after cardiopulmonary bypass. Injections were delivered through the proximal infusion port of a 7.5F pulmonary artery catheter, which was situated in either the superior vena cava or the right atrium. Monitored variables included the electrocardiogram, mean arterial, central venous, and pulmonary artery pressures, end-tidal carbon dioxide and inspired oxygen concentrations, and temperature. Blood was sampled continuously at either the radial artery alone or both the radial artery and aortic root at 2 mL/4.3 s. The difference in magnitude between the maximal potassium concentration achieved and the prebolus baseline potassium concentration (delta K) was correlated with cardiac output, stroke volume, and prebolus baseline potassium concentration (baseline [K+]), using simple linear regression analysis. Although significant hyperkalemia (eg, 7 to 9 mEq/L) developed in both the aortic root and radial artery, this was of no electrocardiographic or hemodynamic consequence, presumably because of the transient nature of the hyperkalemic response, following bolus injection of KCl. There was no significant correlation between delta K and cardiac output or stroke volume; however, delta K did correlate significantly with the Baseline [K+] in a direct linear relationship. It is concluded that central bolus injections of KCl through the proximal infusion port of the pulmonary artery catheter at 33 microEq/kg are safe. This technique should be used cautiously in patients with extremely low cardiac outputs or where intracardiac shunting of blood may exist, as these situations could potentially result in greater hyperkalemic responses than those observed in the current study.

Adult↗
PubMed1993

Potassium iodate and its comparison to potassium iodide as a blocker of 131I uptake by the thyroid in rats.

Potassium iodide is the preferred thyroid blocker for personnel handling radioiodine and is recommended as a prophylaxis for the population in the near-field of a nuclear reactor which would be likely to be exposed to radioiodine in an accidental breach of containment. However, in hot and humid climates, this hygroscopic chemical has a poor shelf life due to hydrolytic loss of iodine vapors. On the other hand, another iodine-rich salt, potassium iodate (KIO3), is quite stable and has a much longer shelf life. The present study compares potassium iodide and KIO3 as thyroid blockers and examines the appropriate time at which they should be administered in case of radioiodine exposure. Either of the two were given in recommended dosage (100 mg stable iodine per 70 kg body weight) at -2, 0, +2, +4, +6, and +8 h after administration of tracer quantities of radioiodine (131I) to age-, weight-, and sex-matched rats. 131I uptake in thyroid was measured 24 h after its administration in the experimental animals and compared with placebo administered controls. Results suggest that KIO3 is as effective a thyroid blocking agent as potassium iodide. In comparison to controls, 24-h thyroid uptake of 131I can be substantially reduced if potassium iodide or KIO3 is given to the animals within 2-4 h after exposure to 131I. Another noteworthy observation is that KIO3 is effective even at 8 h when administered at twice the usual dosage in comparison to the single dose, which does not show appreciable thyroid blocking properties after 8 h.

Animals↗
PubMed1982

Occlusion of rubidium ions by the sodium-potassium pump: its implications for the mechanism of potassium transport.

1. The occlusion of rubidium ions by Na, K-ATPase has been investigated by suspending enzyme prepared from pig kidney outer medulla in media containing low concentrations of (86)Rb, forcing the suspensions rapidly through small columns of cation-exchange resin, and measuring the amounts of radioactivity emerging from the columns.2. When the suspension media contained 2 mM-ATP or ADP, or 15 mM-NaCl, the amounts of radioactivity emerging from the columns were greatly (and similarly) reduced, presumably because both nucleotides and sodium ions stabilized the enzyme in the E(1) form. (See p. 19 for definition of E(1) and E(2)). The extra radioactivity carried through the columns when nucleotides and sodium were absent was taken as a measure of the amount of rubidium occluded within the enzyme (in the E(2) form) when it emerged from the resin.3. By varying the flow rate, and therefore the time spent by the enzyme on the resin, and relating this to the amount of radioactivity emerging from the columns, we have been able to estimate the rate constant for the conformational change (E(2) --> E(1)) that allows the occluded rubidium ions to escape. At 20 degrees C, and in the absence of nucleotides, it is about 0.1 S(-1).4. The rate constant for rubidium release was the same in a sodium-containing as in a potassium-containing medium. The opposite effects of sodium and potassium ions on the poise of the equilibrium between the E(1) and the E(2) forms of the enzyme must, therefore, be due solely to opposite effects of these ions on the rate of conversion of E(1) to E(2).5. The rate constant for rubidium release was greatly increased by ATP and by ADP. Both nucleotides appeared to act at low-affinity sites and without phosphorylating the enzyme.6. Orthovanadate, in the presence of magnesium ions, stabilized the enzyme in the occluded-rubidium (E(2)Rb) form.7. Ouabain, in the presence of magnesium ions, prevented the occlusion of rubidium ions.8. We have measured the amount of rubidium occluded by the enzyme as a function of rubidium concentration, and estimate that at saturating rubidium concentrations about three rubidium ions can be occluded per phosphorylation site (or per ouabain-binding site).9. We have found that the occluded-rubidium form of the enzyme can also be formed by allowing rubidium ions to catalyse the hydrolysis of phosphoenzyme generated by the addition of ATP to enzyme suspended in a high-sodium medium.10. The properties of the occluded-rubidium form of the enzyme, and of the two routes that can lead to its formation, suggest that an analagous occluded-potassium form plays a central role in the transport of potassium ions through the sodium-potassium pump. This hypothesis is supported by a detailed consideration of the probable magnitudes of the rate constants of the individual reactions making up the two routes.

Adenosine Diphosphate↗
PubMed1978

The effects of potassium supplements, spironolactone of amiloride on the potassium status of patients with heart failure.

Extra potassium supplements, spironolactone or amiloride were given for 5 months to forty-nine patients with heart failure who were taking furosemide and were in a steady state. Plasma potassium increased with all three treatments but there was no significant increase in total body potassium or red cell potassium. These findings together with other studies suggest that patients with heart failure taking diuretics do not have a significant depletion of body potassium.

Adult↗
PubMed1992

Chemical characterization of a potassium hydroxyapatite prepared by soaking in potassium chloride and carbonate solutions.

A potassium-doped synthetic apatite was prepared by soaking hydroxyapatite in potassium carbonate and potassium chloride solutions. The hydroxyapatite was prepared by firing slip cast ceramic bodies in vacuum at 1100 degrees C. The conical ceramic samples and a crushed material of this were soaked in carbonate and chloride solutions for 2, 4, 6, and 8 weeks. Potassium, calcium, and phosphate were determined by direct current plasma emission spectroscopy. The carbonate content was determined by thermogravimetric analysis and chloride titrimetrically. After 2 weeks, one potassium ion substituted one calcium ion when soaked in a carbonate solution. When soaked in the chloride solution substitution occurred to the same extent. At phosphate sites the substitution of phosphate for carbonate occurred at one sixth of the sites after 2 weeks. Chloride incorporated one half of the OH-sites after 2 weeks. After 4 weeks about one chloride ion was found in the apatite, and after 6 weeks one and a half of the OH-sites were occupied by chloride ions.

Carbonates↗
PubMed1992

Expression of the H-ras oncogene induces potassium conductance and neuron-specific potassium channel mRNAs in the AtT20 cell line.

Expression of the EJ-ras oncogene in the AtT20 cell line results in several changes in their properties that correspond to a switch of these anterior pituitary-derived cells to a more neuronlike phenotype. The width of action potentials following transfection with ras is reduced 20-fold from over 200 msec in control AtT20 cells to less than 10 msec in ras-transfected cells. This is associated with a two- to threefold increase in the density of voltage-dependent potassium currents. In addition, the rate of inactivation of these currents is decreased approximately twofold in ras-transfected cells. At least part of the change in potassium current may be due to differential expression of potassium channel mRNAs. In the ras-transfected cells, mRNA species were detected using a probe for the voltage-dependent potassium channels, Kv4, a species that appears to be uniquely expressed in the nervous system, and NGK2, an alternatively spliced product transcribed from the same gene. These mRNAs are not detected in control AtT20 cells. The results suggest that the ras protein modulates the phenotype of excitable cells by influencing the expression of specific potassium channels and thereby altering the density and types of channels in the plasma membrane.

Electric Conductivity↗
PubMed1993

Modulation of sodium-potassium adenosine triphosphatase in cultured bovine retinal pigment epithelium by potassium.

PURPOSE: The aim of the study was to examine the extracellular potassium concentration [K+]o as a modulator of the retinal pigment epithelium (RPE) contribution to ion homeostasis in the subretinal space by measuring sodium-potassium adenosine triphosphatase (Na+/K+ ATPase) pump number and activity in cultured bovine RPE in the presence of different concentrations of extracellular potassium. METHODS: Pump number was quantified by measuring specific binding of 3H-ouabain to bovine RPE exposed to low (0.5-2.5 mmol) or control (5.0 mmol) [K+]o over 72 hr. Na+/K+ ATPase activity in low and control [K+]o was quantified by measurement of 86Rb+ uptake. RESULTS: Low [K+]o increased RPE pump number in a dose- and time-dependent manner, with lesser effects on denser than on sparser cultures. [K+]-modulation of pump number was reversible and did not occur in the presence of the protein synthesis inhibitor cycloheximide. In RPE exposed to low [K+]o for 72 hr, pump activity was decreased compared with the control but increased toward control levels when re-exposed to control [K+]o. The total potassium transported per cell was 60% of control in low [K+]o but increased to slightly above control when re-exposed to control [K+]o. CONCLUSIONS: In cultured RPE cells, both Na+/K+ ATPase pump number and pump activity are affected by changes in [K+]o, with greater modulation in sparser cultures. If similar events occur in situ, the sodium pump in RPE may respond to changes in subretinal potassium ion concentration, especially if the RPE cell number is reduced as in aging or disease.

Animals↗
PubMed1989

Replacement of potassium ions by ammonium ions in different micro-organisms grown in potassium-limited chemostat culture.

The biomass concentration extant in potassium-limited cultures of either Klebsiella pneumoniae or Bacillus stearothermophilus (when growing at a fixed temperature and dilution rate in a glucose/ammonium salts medium) increased progressively as the medium pH value was raised step-wise from 7.0 to 8.5. Because the macromolecular composition of the organisms did not vary significantly, this increase in biomass could not be attributed to an accumulation of storage-type polymers but appeared to reflect a pH-dependent decrease in the cells' minimum K+ requirement. Significantly, this effect of pH was not evident with cultures in which no ammonium salts were present and in which either glutamate or nitrate was added as the sole nitrogen source; however, it was again manifest when various concentrations of NH4Cl were added to the glutamate-containing medium. This suggested a functional replacement of K+ by NH4+, a proposition consistent with the close similarity of the ionic radii of the potassium ion (1.33 A) and the ammonium ion (1.43 A). At pH 8.0, and with a medium containing both glutamate (30 mM) and NH4Cl (100 mM), cultures of B. stearothermophilus would grow without added potassium at a maximum rate of 0.7 h-1. Under these conditions the cells contained maximally 0.1% (w/w) potassium (derived from contaminating amounts of this element in the medium constituents), a value which should be compared with one of 1.4% (w/w) for cells growing in a potassium-limited medium containing initially 0.5 mM K+.(ABSTRACT TRUNCATED AT 250 WORDS)

Culture Media↗
PubMed1987

Serum magnesium and potassium levels in hypertensive patients after a therapeutic switch from hydrochlorothiazide plus a potassium supplement to maxzide.

Determinations of serum magnesium and potassium levels and blood pressure were made in 40 hypertensive patients in whom daily therapy with 50 mg of hydrochlorothiazide plus potassium supplements was switched to a once-daily regimen of 50 mg of hydrochlorothiazide plus 75 mg of triamterene (Maxzide). Patients showed no clinically significant changes in blood pressure or in serum magnesium or serum potassium values following the switch. It is concluded that therapy in patients receiving hydrochlorothiazide and up to 60 meq of potassium can be safely switched to Maxzide without adversely affecting serum magnesium levels, serum potassium levels, or blood pressure control.

Adult↗