42K Efflux Research Articles

The movement of potassium ions during electrical activity, and the kinetics of the recovery process, in the non‐myelinated fibres of the garfish olfactory nerve.

1. An electrophysiological study was made with the sucrose gap of the compound action potential of the non-myelinated fibres of the garfish olfactory nerve at temperatures between 8 and 22 degrees C. The efflux of 42K with stimulation, and the post-tetanic hyperpolarization following a period of repetitive stimulation, were also studied. 2. At 22 degrees C the compound action potential (at zero conduction distance) reached its peak in about 5 msec and lasted about 12 msec; the conduction velocity was 19.4 cm/sec. The corresponding extrapolated values at 0 degrees C were: time to peak, 16 msec; duration, 37 msec; conduction velocity, 4.2 cm/sec. 3. The rate constant for resting potassium efflux (kr) was 0.0108 min-1 at 22 degrees C and 0.00489 min-1 at 0 degrees C. 4. The extra fractional loss of potassium with stimulation (ks) was 2.02 x 10(-4) impulse-1 at 22 degrees C and 4.41 x 10(-4) impulse-1 at 0 degrees C. 5. Raising the external potassium concentration, or addition of ouabain (1 mM), raised the resting rate of efflux of potassium. 6. The post-tetanic hyperpolarization, which reflects the electrogenic extrusion of sodium ions, indicated a rate constant for active sodium efflux at 22 degrees C of 0.47 min=1. 7. The rate constant was decreased by a 10 degrees C fall in temperature by a factor of 1.73. 8. Increasing the external potassium concentration increased the rate constant, apparently by potassium combining with some site with an equilibrium dissociation constant of 1.2 mMM. 9. The rate constant was decreased slightly in acidic solutions and increased slightly in alkaline solutions. 10. 14C-labelled ouabain was found to bind to the garfish olfactory nerve with an equilibrium dissociation constant of about 0.5 muM. The maximum saturable binding capacity, 22.3 p-mole/mg dry, suggests that there are about 350 sodium pumping sites per square micron membrane.

Increase of potassium flux by valinomycin in embryonic chick heart.

The effect of different concentrations of the antibiotic valinomycin, was determined on 42K efflux and Na, K content of embryonic chick hearts. Valinomycin produces an increase of K efflux which is progressive in time and markedly dependent on the concentration of external K (0-5 mM) and valinomycin (10(-8) to 10(-5) M). The changes in K efflux is not due to a reversal of the Na-K pump mechanism, secondary to ATP depletion: i) the increase of K efflux by valinomycin persists in the absence of external Na ions. ii) analysis of Na and K content and 42K influx measurements with and without valinomycin indicate that active K influx is not inhibited in a solution containing 0.5 mM K and only slightly decreased in a solution containing 5 mM K. Valinomycin, acting as a K carrier, presumably increases K conductance of the cell membrane resulting in a rise in K efflux.

42K efflux, EKG and tension in isolated perfused hearts of white-footed mice

1. 1. The EKG and systolic tension of isolated, perfused hearts from Peromyscus leucopus is a function of the perfusion temperature. 2. 2. The marked loss of 42K during perfusion at lower temperatures indicates a loss of intracellular potassium and suggests a breakdown in the ability to maintain electrolyte balance. 3. 3. The decline in EKG potential and tension as well as the increased 42K efflux which occur at perfusion temperatures similar to the lower range of body temperature during torpidity of the intact animal indicate that cardiac performance may limit the depth and length of torpor in P. leucopus.

Potassium: potassium exchange catalysed by the sodium pump in human red cells.

1. When red cells were so depleted of Na that Na:K exchange had almost ceased, the ouabain-sensitive K efflux seen in K-containing media was accompanied by an almost equal ouabain-sensitive K influx.2. This suggests that the Na pump in these cells was carrying out a one-for-one K:K exchange across the erythrocyte membrane.3. 30-40% of the (42)K efflux from resealed ghosts was sensitive to ouabain when the ghosts contained 1 mM-ATP, 2 mM orthophosphate, 10 mM-K and less than 1 mM-Na, and the suspending medium contained 10 mM-K and 0-Na, choline being the predominant cation.4. In resealed ghosts, the rate of K:K exchange saturated as internal K was increased, and was half-maximal at about 10 mM-K.5. When internal ATP was maintained with a phosphocreatine:creatine phosphokinase regenerating system, K:K exchange saturated as internal ATP was increased, and was half-maximal at about 100 muM-ATP.6. The rate of K:K exchange did not depend on whether the ADP concentration was roughly the same as the ATP concentration or very much less, suggesting that ADP did not affect the rate of K:K exchange.7. GTP, ITP and UTP were unable to substitute for ATP in supporting K:K exchange. CTP was a poor substitute.8. There was no evidence to support the hypothesis that K:K exchange is accompanied by a ouabain-sensitive hydrolysis of ATP.9. Internal Na was a strong inhibitor of ouabain-sensitive K efflux from ghosts containing 9 mM-K. 4 mM-Na was sufficient to produce 90% inhibition.10. The rate of K:K exchange depended on the orthophosphate concentration inside the ghosts (confirming Glynn, Lew & Lüthi, 1970). The curve obtained suggested that the rate was half-maximal at about 1.7 mM orthophosphate.11. These experiments suggested that inhibition by internal K is an important factor affecting the Na efflux from intact red cells. Experiments measuring Na:K exchange as a function of internal Na in low-K ghosts supported this hypothesis.12. The significance of these findings is discussed.

Liberation of acetylcholine by ouabain in the cat submandibular gland.

The ability of ouabain to initiate loss of potassium and salivary secretion from the perfused cat submandibular gland has been studied in the absence and presence of atropine. Ouabain (10−4 M) when given alone caused a net efflux of potassium amounting to 4.25 μEq×min−1×g−1 and induced salivary secretion. When ouabain was given together with atropine (7.2×10−5 M) the net efflux of potassium was 1.00 μEq×min−1×g−1 while no saliva was secreted. In glands loaded with42K the rate constant of the efflux of42K was increased when the perfusion fluid contained ouabain. When atropine was given before and during administration of ouabain, there was no change in the rate constant. The results indicate that ouabain causes a liberation of acetylcholine, which in turn increases the permeability of the glandular cells to potassium and elicits salivary secretion.

The mechanism of energy-dependent ion transport in mitochondria

The transport of potassium, sodium and various anions in rat-liver mitochondria was studied mainly by analysis of ion content and water compartmentation of the mitochondrial pellet. A comparison of spontaneous transport with valinomycin- or gramicidin-stimulated transport is made. The rate or extent of uptake, the internal concentrations and the concentration ratio (Cin/Cout) are calculated and compared to test existing models for ion transport in mitochondria. Several models of ion transport in mitochondria are based on a cation-pump which is directed inward. This hypothesis is rejected because of the following findings: (1) Valinomycin stimulates the rate of potassium uptake but does not increase the potassium concentration ratio that can be actively maintained in a steady state (in which there is no potassium flow). (2) Valinomycin greatly stimulates the efflux of42K from mitochondria during the process of potassium accumulation. When potassium accumulation is stimulated the flux ratio, i.e. influx/efflux, decreases; in the presence of valinomycin this ratio approaches 1. (3) In the presence of gramicidin, the concentration ratios of potassium and sodium are about the same under a variety of conditions. These findings indicate that potassium and sodium transport are passive processes of relaxation towards electro-chemical equilibrium (of the potassium and sodium). In high external potassium concentrations the extent of potassium uptake is limited by the permeation of anions; of the permeating anions multivalent acids support a higher extent than monovalent acids. It was found that succinate, acetate and oxalate which are transported together with potassium are distributed in accordance with the ΔpH and without any relation to the potassium concentration ratio. These findings are compatible with the hypothesis that an outward-directed proton pump creates an electrical potential gradient, which shifts the equilibrium state for the cations and drives sodium and potassium inward, and also creates proton gradient that is the driving force for anion transport.

Efflux of potassium from isolated rod outer segments: a photic effect

1. Illumination of the isolated outer segments of rod photoreceptors loaded with (42)K or (86)Rb reduces the efflux of these ions.2. During the perfusion of the isolated rod outer segments with a solution containing only 2.36 mM-Na the effect of light is absent, and the amplitude of the photic effect is linearly related to the logarithm of the extracellular Na concentration.3. In darkness, raising the concentration of K in the fluid of perfusion gives an increase of the efflux of (86)Rb and increasing the extracellular concentration of Ca yields a retention. The efflux of (86)Rb and (42)K is greater in darkness when sucrose or choline substitute for Na.4. It is suggested that in darkness the isolated outer segments are permeable both to Na and to K. Light appears to decrease the permeability for Na ions. There is no evidence that the permeability for K ions is modified by light.

Ion distribution and the role of calcium in cellular function. Ion distribution and ion movements in smooth muscle.

The steady-state fluxes of K + , Cl - and Na + from smooth muscles in normal Krebs solution are described, and some of the problems encountered in the interpretation of such results are discussed. Sodium fluxes are particularly difficult to analyse, and the type of model used to estimate sodium permeability from flux curves, determines the value calculated to a large extent. In order to simplify the ionic distribution in the tissue, in the hope of obtaining more information about the handling of Na and K by the guinea-pig taenia coli, potassium-free (high Na) tissues and sodium-free (high K) tissues were prepared by soaking for 4 h in the relevant solution. The tissues reach a steady state, and the effluxes of 42 K from high K tissues and 24 Na from high Na tissues were measured and compared. In these two conditions the electrochemical gradients for Na + and for K + are probably identical. Nevertheless, the fluxes are markedly different. At 37 °C the Na flux is much faster than the K flux, and a part of the Na exchange is very temperature sensitive. There is also some evidence for a sodium calcium exchange mechanism. It is hoped that further experiments will produce results that will help to understand the processes involved in these exchanges.

Illumination of the isolated frog retina and efflux of tracer potassium and rubidium

The efflux of 42K and 86Rb from the isolated frog retina is influenced in a complex way by illumination. In particular, there is a transient decrease of the efflux at the onset of illumination. The effect is present when the retina is illuminated with an intensity in the physiological range of vision, and for dim intensity the effect is promptly reversible.

The effects of changes in the ionic environment on venous smooth muscle distribution of sodium and potassium.

AbstractThe sodium, potassium, calcium and magnesium content in the portal vein of the rat was determined by atomic absorption spectrophotometry in different environmental conditions. It was found that minute changes in the ionic environment caused considerable variations in the Na+, K+ and Ca2+ content, and Na/K ratio. Phosphate in the solution increased the sodium and calcium content. In sodiumfree solution all muscle sodium was rapidly lost. No bound sodium was detected. The ionic content of portal vein was also dependent on dissection and blotting technique. A standard procedure and a standard solution was therefore chosen. In this solution the following values were obtained: Na+: 88, K+: 52, Ca2+: 5.7 and Mg2+: 3.7 mmolelkg freshweight respectively.The extracellular space, determined with 14C‐sorbitol was 490 ml/kg freshweight. The calculated intracellular concentrations and equilibrium potentials for Na+ and K+ were 62 and 157 mM and +21 and ‐86 mV respectively. The uptake of 42K showed that about 20 % of the total muscle potassium did not exchange within 5 hrs. The efflux of 42K+ showed that for the linear exchange of muscle potassium the rate constant was 0.85–0.90/hr.K‐low solution decreased the efflux of 42K+ in spite of increased electrical activity. This suggests that the permeabilty to potassium is lowered. Noradrenaline had no effect on the 42K efflux in normal solution.

COMPARTMENTATION AND LOW TEMPERATURE FLUXES OF POTASSIUM IN MYCELIUM OF DENDRYPHIELLA SALINA

Summary Dendryphiella salina was grown at 21° C in two media, identical except that one contained potassium labelled with 42K. The cultures were transferred to 2° C, the fungus separated from the medium, the radioactive mycelium placed in the non‐radioactive medium and the efflux of 42K measured. Under these conditions the rate of dry weight increase is reduced by at least 75%. The fungus behaves as a multicompartment system with regard to potassium with at least 75% of the ion being in the slowest‐exchanging compartment. The efflux from this compartment into a medium containing 2.5 mM potassium is of the order of 0.14 p moles cm−2 sec−1, being at least doubled when 50 mM sodium is present. Addition of 10 mM calcium in the presence of sodium reduces the efflux to a value close to that obtained when sodium is absent.

Strophanthidin sensitivity of frog sartorius muscles in sodium-and potassium-free solutions

Substitution of Tris-Cl for NaCl in K +-free Ringer solution resulted in a reduction of the rate of 42K efflux from 0.057 hr −1 to 0.017 hr −1 and a hyperpolarization of the resting membrane potential (E m) from −118 mV to −144 mV in frog sartorius muscles. The hyperpolarization and reduction of potassium efflux were reversed by the addition of strophanthidin (10 −5M) when the muscles had been previously sodium-enriched. It was concluded that the very low rate of 42K efflux in the K +-and Na +-free solution was probably associated with an increased reuptake of potassium ions which was strophanthidin sensitive.

The Effect of Temperature on Sodium Movements in Rat Uteri and a Model for Control of their Ion Content

The uptake and efflux of 22Na was studied in isolated rat uterine horns (both fresh and Na-rich) at 5, 15, 25, and 37 °C. Reduction of temperature from 37 °C to 25 or to 15 °C reduced 22Na uptake into, and efflux from, both the extracellular space and cells to the degree expected of a diffusion-controlled process (Q10 < 2). Reduction of the temperature to 5 °C during uptake into Na-rich horns revealed that a substantial fraction of cellular sodium became less exchangeable. At 5 °C, 22Na efflux was also markedly reduced, more than from ouabain or ATP depletion. Analysis of this change by curve-peeling and by reducing the temperature at various stages of efflux suggested that the main cause was a shift of 22Na from the larger, faster cellular fraction (No. 2) to the slower cellular fraction (No. 3). Bound 22Na was also markedly increased. The rate coefficients from curve-peeling for both cellular fractions were decreased. Radioactivity still in fraction 2 at 5 °C emerged at a rate of about half that at 15 °C. However, an overall coefficient for efflux of 22Na which would have emerged in fraction 2 at 15 or 25 °C showed that the Q10 for 22Na efflux between 5 and 15 °C was about 15. Tissues did not swell when they gained sodium at 5 °C. The effects of ouabain to increase 22Na influx and 42K efflux were eliminated at 5 °C. The effects of ATP depletion by iodoacetate and dinitrophenol to decrease 22Na efflux and to increase 22Na uptake, K loss, and swelling were reduced at 5 °C. Prior ATP depletion altered but did not prevent the marked reduction of efflux by cooling to 5 °C. Efflux of lithium, but not of potassium, was markedly slowed at 5 °C. K-free solutions still increased 22Na uptake at 5 °C. A model involving pinocytotic vesicles to explain these and earlier results was postulated.

Action of steroidal diamines on active transport and permeability properties of Escherichia coli.

The steroidal diamine irehdiamine A (IDA) is a potent inhibitor of bacteriophage growth and macromolecular synthesis in Escherichia coli. By using radioactive (42)K and (14)C-thiomethylgalactoside (TMG), rapid effects of IDA and related steroids, both on the influx of potassium and TMG via their respective transport systems and on the efflux (leakage) of radioactivity from the treated cells, have been measured. IDA affects both the influx and efflux of (42)K at concentrations of steroid as low as 2 x 10(-5)m. Because of the increased leakage, it is not possible to tell whether there is a direct effect reducing the rate of active transport of potassium. The primary diamine, IDA, and its bis-secondary, bis-tertiary, and bis-quaternary diamine analogues are decreasingly effective in altering cell permeability properties in the order 1 degrees > 2 degrees > 3 degrees > 4 degrees . The effects of IDA on potassium transport are mirrored by similar effects on the transport of TMG. Therefore, the action of IDA is on the cell membrane and not directly on one or another transport system. The effects of IDA on cell permeability can reasonably explain the inhibitory actions of the drugs on bacteriophage growth and cellular metabolism.

Potassium ions and the secretion of insulin by islets of Langerhans incubated in vitro.

1. A method was devised for the isolation of islets of Langerhans from rabbit pancreas by collagenase digestion in order to study the influx and efflux of K(+) in islets during insulin secretion. 2. Glucose-induced insulin release was accompanied by an increased rate of uptake of (42)K(+) by the islets of Langerhans, though this was not the case for secretion in response to tolbutamide. Ouabain significantly inhibited the uptake of (42)K(+) by islet tissue. 3. No significant increase in the rate of efflux of (42)K(+) was demonstrated during active insulin secretion. 4. Slices of rabbit pancreas were incubated in media of different K(+) content, and rates of insulin release were determined. Alteration of the K(+) concentration of the medium between 3 and 8mm had no effect on the rate of insulin release by pancreas slices. However, decrease of the K(+) concentration to 1mm resulted in inhibition of secretion in response to both glucose and to tolbutamide. Conversely, an increase in K(+) concentration increased rates of insulin release in response to both these stimuli. 5. It is concluded that, though unphysiological concentrations of K(+) may influence the secretion of insulin, fluxes of K(+) in the islets do not appear to be important in the initiation of insulin secretion.

Long duration responses in squid giant axons injected with 134cesium sulfate solutions.

Giant axons from the squid were injected with 1.5 M cesium sulfate solutions containing the radioactive isotopes 42K and 134Cs. These axons, when stimulated, gave characteristic long duration action potentials lasting between 5 and 45 msec. The effluxes of 42K and 134Cs were measured both under resting conditions and during periods of repetitive stimulation. During the lengthened responses there were considerable increases in potassium efflux but only small increases in cesium efflux. The selectivity of the delayed rectification process was about 9 times greater for potassium ions than for cesium ions. The data suggest that internal cesium ions inhibit the outward potassium movement occurring during an action potential. The extra potassium effluxes taking place during excitation appear to be reduced in the presence of cesium ions to values between 7 and 22% of those expected in the absence of cesium inhibition.

THE EFFECT OF ADRENALINE ON THE K AND NA FLUXES IN THE FROG'S ATRIUM.

In frog's atria the effects of adrenaline on the Na and K transmembrane resting fluxes, the volume of the inulin space, the intracellular Na and K concentrations, and the membrane potential were studied. The following results were obtained: 1. Adrenaline increased the loss of 24Na by 10 to 20% and decreased 24Na uptake by 3 to 5%. 2. The inulin space was found to be reduced from 31 to 26% under the influence of adrenaline. 3. The adrenaline induced increase of the loss of 24Na is to be directly related to the flux through the cell membrane. The decrease in the uptake of 24Na is converted into a slightly increased 24Na influx on the cell membrane when the reduction in inulin space is accounted for. 4. Adrenaline results in an augmentation of 42K efflux and influx by 25 and 32%, respectively. 5. Determination of the intracellular Na and K concentrations yields no appreciable changes after adrenaline application but only a slight increase in [Na]i and a small decrease in [K]i. This is in agreement with the flux measurements. 6. Under adrenaline there is tendency to a small hyperpolarization, the duration and the shape of action potential being virtually unchanged.

THE EFFECTS OF CHANGE IN IONIC MILIEU AND ELECTRICAL STIMULATION ON THE IONIC MOVEMENTS IN SMOOTH MUSCLE.

Sodium and potassium movements in the isolated preparation of guinea-pig's taenia coli soaked in high KCl Krebs solution and LiCl Krebs solution were estimated. In high KCl Krebs solution, both inward and outward movements of 42K were increased in proportion to the degree of depolarization. In LiCl solution 42K uptake was reduced though 24Na uptake was not influenced, 42K efflux increased and 24Na efflux was reduced slightly. The electrical stimuli of both 1V/cm and 10V/cm were effective to increase the efflux of 42K of taenia coli immersed in normal Krebs and in K2SO4 Krebs solutions, although in the latter medium, 1V/cm stimulus was ineffective to cause contraction. 24Na efflux was also increased by 10V/cm electrical stimulation in normal and in K2SO4 Krebs solution, though the change was not so significant as 42K results.

THE EFFECTS OF TEMPERATURE AND SOME DRUGS ON THE IONIC MOVEMENTS IN THE SMOOTH MUSCLE OF GUINEA-PIG TAENIA COLI.

Sodium and potassium movements in smooth muscle of guinea-pig taenia coli were measured with radioactive isotopes. In low temperature (20°C and 2°C), uptake of 42K and loss of 24Na were reduced considerably, but loss of 42K and uptake of 24Na were not so much affected. Adrenaline (1×10-5g/ml) had no significant effect upon the movement of 24Na, though it had suppressed the spontaneous contraction completely. Acetylcholine, adrenaline, histamine and serotonin also increased the efflux of 42K.

Quantitative analysis of movements of potassium in rabbit auricles.

When rabbit auricles are isolated in physiological saline solution at 29 or 37 °C, the influx or efflux of 42 K follows a course which can be described by the sum of two exponential terms. The presence of an initial fast component is more evident in beating than in spontaneously quiescent auricles, but the fast component is not due to beating because it occurs also in auricles in which beating is stopped by carbachol (2 x 10 -6 M). A small loss of potassium occurs in untreated auricles and a larger one under the influence of certain drugs, such as ouabain (10 -5 M) or dinitrophenol (10 -4 M). Several model systems are considered, especially those with three compartments all or partially communicating with each other, both with regard to exchange of tracer and to net changes in the total ionic content of the compartments. The simplest model which describes the observations had 79 ± 2 (S. E.) % of the tissue potassium free to exchange with the medium and the rest exchanging more slowly with the main fraction. In a steady state at 29 °C, in quiescent left auricles 1⋅07 % of the main fraction exchanged with the medium and 0⋅37 % with the slow fraction per minute. The corresponding rates for beating right auricles were 2⋅25 and 0⋅20 % per minute. In the presence of ouabain (10 -5 M) uptake from the medium to the main fraction was reduced to about 40% of the normal rate, with corresponding net loss of potassium. Dinitrophenol reduced or stopped uptake to the slow fraction and also accelerated loss from the main fraction to the medium.