External Potassium Concentration Research Articles

Potassium induced potential changes in rat diaphragm muscle.

The effect of different potassium concentrations on the membrane potential and membrane resistance of rat diaphragm muscle fibres was measured by means of a double sucrose gap method and a microelectrode technique. Concentration measurements showed that the muscle fibres gained sodium and lost potassium in the equilibration period. In the absence of external chloride changing the external potassium concentration from 2.8 mM to potassium-free caused a depolarization of the membrane of about 30 mV and a small increase in membrane resistance. This K-dependent potential change (K-response) was induced by ouabain, K-strophanthin, 2,4-dinitrophenol and cyanide, indicating that an energy requiring process is involved. The temperature dependence of the K-response found is consistent with this assumption. Variation in potassium permeability in the absence and presence of external potassium could account for only 13% of the K-response. The K-response amplitude appeared to depend on the external potassium and the internal sodium concentration. Hyperpolarization of the membrane could not only be produced after readmission of potassium but also after addition of thallium, the latter being more potent. Raising the external chloride concentration resulted in a decrease of the K-response and membrane resistance. The current, generating the K-response was shown to be hardly influenced by conditional polarization of the membrane. It is concluded from these results that the K-response is mainly due to the operation of an electrogenic sodium pump.

Ionic dependence of sodium currents in squid axons analyzed in terms of specific ion "channel" interactions.

Inward sodium currents were measured from voltage-clamped giant axons externally perfused with artificial seawater (ASW) solutions containing various concentrations of sodium and potassium ions. The data was analyzed under the assumption that under a constant membrane potential sodium conductance is determined by a specific ion-channel site (SIS) reaction. The sodium current density values were expressed in terms of SIS-reaction rates which were compared, by means of minimization techniques, with those computed for various saturation reaction mechanisms. The following conclusions were drawn: 1) The dependence of peak inward sodium current on external sodium and potassium concentrations can be described in terms of saturation reactions. 2) The experimental data fit well the kinetics of a positive cooperative homotropic reaction, involving at least two allosteric active sites. One of these sites may be catalytic while the other, either catalytic or regulatory. 3) The inhibitory effect of external potassium on inward sodium current, can be described by a reversible competitive or noncompetitive inhibition mechanism. The values of the dissociation constant of the inhibitor-site "complex" (Ki) were found to be close to the external potassium concentration under physiological conditions.

The effect of external potassium concentration on leucocyte cation transport in vitro.

1. Sodium and potassium transport rates in human leucocytes were measured in vitro at different external potassium concentrations. 2. At nominally zero external potassium concentrations, the ouabain-sensitive sodium efflux was reduced to less than 20% of its maximum value. There was evidence that under these conditions a ouabain-sensitive sodium-sodium exchange occurs. 3. Both total and ouabain-insensitive potassium influx increased with increasing external potassium concentration. The ouabain-sensitive potassium influx showed saturation. 4. Ouabain-insensitive potassium efflux was also stimulated by increasing the external potassium concentration, suggesting significant potassium-potassium exchange at physiological external potassium concentrations.

Influence of potassium ions and osmolality on the resting membrane potential of rabbit ventricular papillary muscle with estimation of the activity and the activity coefficient of internal potassium.

Resting membrane potentials of rabbit right ventricular papillary muscles were measured in modified Tyrode's solutions that were isotonic (1.0 X T), hypertonic (1.58 X T), or hypotonic (0.76 X T) at eight different concentrations of external potassium, [K]o, ranging from 0.78 to 100 mM. The amount of hyperpolarization produced by exposure to the hypertonic solutions was relatively constant with an average of 4.6 mv at all levels of [K]o except 0.78 and 1.56 mM. This potential change is much less than the 10.6 mv which would be predicted if the papillary muscles behaved as nearly perfect osmometers and the activity coefficient of intracellular potassium (K) remained constant. The amount of depolarization produced by exposure to the 0.76 X T hypotonic solutions averaged 6.8 mv at all levels of [K]o except 0.78 mM; this value is close to the predicted value of 6.9 mv. Variations in the activity and the activity coefficient of intracellular K were introduced to explain these discrepancies. We estimated that the activity of intracellular K in 1.58 X T hypertonic solution was increased 15-23% compared with that in isotonic solution. This change is much less than the 58% that would be predicted if the papillary muscle behaved as a nearly perfect osmometer. We also estimated that the activity of intracellular K in 0.76 X T hypotonic solution fell 22-26%, which is very close to the predicted value of 24%. The activity coefficient of intracellular K appeared to fall in 1.58 X T hypertonic solution to about 0.76 of its value in isotonic solution. This decline in the estimated activity coefficient of intracellular K could not be attributed to an increase in Coulombic attractive and repulsive forces as predicted by the Debye-Hückel equation for a univalent electrolyte.

Ion fluxes during the inhibitory junction potential in the guinea-pig taenia coli.

1. Contribution of different ions to the inhibitory junction potential (i.j.p.) in the guinea-pig taenia coli was studied by measuring the 42K, 24Na and 36Cl fluxes, the membrane resistance and the influence of various external ion concentrations. 2. The membrane resistance, as measured by the electrotonic potential, decreased transiently during the i.j.p. A maximal reduction of the electrotonic potential of about 50% was found at the top of the i.j.p. 3. The i.j.p. amplitude could be reduced by raising the external potassium concentration. Extrapolation of the relationship observed shows that the inhibitory response would be abolished at 115 mM potassium. Similar experiments were made in chloride-free medium, chloride being replaced by isethionate. Amplitude and time course of the response were not different in chloride containing Locke solution and chloride-free medium. 4. The half-times of 42K, 24Na and 36Cl effluxes during rest were 29, 10 and 9 min respectively. The 42K-efflux from the preparation was markedly increased to about three times the resting efflux during field stimulation. In low-chloride solution a similar effect on 42K-efflux was observed during field stimulation. Only a slight increase in the chloride efflux was observed but the sodium efflux was not affected during field stimulation. 5. From the results presented it is concluded that the inhibitory junction potential is caused by a selective increase in potassium permeability of the smooth-muscle cell membrane.

Potassium activation in Helix aspersa neurones under voltage clamp: a component mediated by calcium influx.

1. Helix aspersa neurones under voltage clamp generate prolonged outward currents (potassium currents) in response to depolarizing command pulses. 2. The potassium currents recorded from cell A were reversibly reduced 25-50% by 10 mM cobalt ions in the bathing medium; 1 mM lanthanum, 10(-6) g/ml. D-600 and 10(-6) g/ml. iproveratril had similar effects but were only partially reversible. 3. The relationship between the potassium currents and the membrane potential had an "n" shape in normal saline. In calcium-free saline (containing 25 mM magnesium) the potassium currents were reduced and the "n" shape was abolished. The effect of calcium-free saline was readily reversible. 4. The voltage-dependence of the calcium-sensitive potassium currents was similar to that of the "late" calcium channel in squid axons (Baker, Hodgkin & Ridgway, 1971). 5. When cell A was depolarents were made up of two exponentially declining components. The slower of the two components was reduced in calcium-free saline. 6. When cell A was depolarized by 150 mV for 10 msec and then repolarized the "tail" currents were made up of a single rapidly declining component. The reversal potential of this component changed by 58 mV for a tenfold change in the external potassium concentration as predicted by the Nernst equation. 7. The reversal potential of "tail" currents having both components was less sensitive to changes in the external potassium concentration. 8. Tetraethylammonium (TEA) ions blocked both calcium dependent and voltage sensitive potassium currents. Each receptor was found to bind a single molecule of TEA. The dissociaton constant was about 10 mM in each case. 9. The intracellular concentration of ionized calcium was estimated from the potential at which there was no apparent calcium influx (the null point). It was between 3 x 10(-8) M and 8 x 10(-8) M with 10(-2) M calcium in the bathing medium. 10. The null point changed 30 mV for a tenfold change in the external calcium concentration as predicted by the Nernst equation. 11. It is concluded that depolarization of Helix neurones activates two typesof potassium channel. One channel is voltage dependent and highly selective for potassium. Activation of the other channel is dependent on the influx (or injection, see Meech, 1972, 1974a) of calcium. This calcium mediated potassium activation system saturates at high external calcium concentrations and is inhibited by external magnesium ions.

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.

Relation of Intracellular K+ and Steroidogenesis in Isolated Adrenal Zona Glomerulosa and Fasciculata Cells

1. Intracellular K+ content, water spaces and corticosterone output were measured in isolated zona glomerulosa and zona fasciculata-reticularis cell suspensions of rat adrenal cortex, after incubation in vitro under conditions designed to alter steroidogenesis. 2. Intracellular K+ of unpurified zona glomerulosa cells was not altered after stimulation of corticosterone output with serotonin. Similarly, with zona glomerulosa cells purified by unit gravity sedimentation, no change in intracellular K+ was detected after stimulation of steroidogenesis with serotonin or angiotensin II. 3. In high-potassium medium (final concentration 8.4 mmol/1), parallel increases in intracellular K+ and corticosterone output were observed with both purified zona glomerulosa cells. However, a similar increase in intracellular K+ also occurred in high-potassium medium with zona fasciculata cells, whose steroid output is unresponsive to external potassium concentration ([K+]). 4. Ouabain at 10(-5) mol/1 depressed the intracellular [K+] of glomerulosa cells but did not alter basal or stimulated corticosterone output. Similar results were obtained with fasciculata cells. 5. Ouabain at 5 times 10(-4) mol/1 further depressed intracellular [K-+] of glomerulosa cells and inhibited basal and stimulated corticosterone output. However, this concentration of ouabain also inhibited steroidogenesis in fasciculata cells. 6. These results demonstrate a variety of situations where changes in intracellular [K+] are dissociated from those in corticosterone output and indicate that intracellular [K+] cannot be the sole mechanism regulating steroidogenesis under these conditions.

In vivo and in vitro miniature end-plate potentials at various external K concentrations.

In order to obtain a nore reliable picture of transmitter release, spontaneous synaptic activity was studied in vivo in the rat soleus neuromuscular junction. The in vivo miniature end-plate potential (MEPP) recordings were compared with those obtained in vitro and, in both circumstances, MEPP frequency was measured at external potassiumconcentrations ranging from 5 to 15 mM. The influence of external potassium loading on intra- and extracellular potassium concentration also estimated by measuring the muscle ionic composition and water distribution at normal and high plasma potassium concentrations. The MEPP frequencies recorded in vivo were consistently lower than those observed in vitro for all external potassium concentrations studied (P less than0.01). These data suggest that better experimental conditions are maintained in thein vivo preparations, since the intracellular potassium increase that follows the external potassium loading can only partially justify the observed differnce and other factors, such as anesthetic effects, etc, may be ruled out.

Stimulus-secretion coupling in an insect salivary gland: cell activation by elevated potassium concentrations.

1. Fluid secretion by isolated salivary glands was stimulated by elevating the external potassium concentration. 2. The stimulatory effect of potassium was dependent on external calcium and was potentiated by a subthreshold dose of 5-hydroxytryptamine (5-HT). 3. During the action of 120 mM potassium there was a large calciumdependent decrease in transepithelial resistance similar to that produced with 5-HT at normal potassium concentrations. 4. These results on Calliphora salivary glands are compared with other cases where cells are activated by high potassium. In most cases, the effect of high potassium is dependent upon calcium, suggesting that the latter plays a primary role in cell activation.

Action potential of the garfish non-mylinated olfactory nerve

The interesting Garfish olfactory nerve has been described by D. Easton (6). His structural analysis of the preparation shows homogeneous, uniform diametered axons measuring about 0.24 microns. The present study is an attempt to characterize its electrical and ionic property. The duration of the extracellularly measured action potential is about 60 msec at 20°C and increases to about 500 msec at 5°C, a time dispersion of about 8X. The conduction velocity varies from 20 cm/sec at 20°C to 4 cm/sec at 0°C. Recordings from small isolated fiber bundles have been shown to be viable. Reduction of sodium concentration to 5 mM in the external medium annihilates the A.P. response. Increase in external potassium concentration to about 16 mM makes the nerve inexcitable.

Interrelationships between external potassium concentration and lidocaine: effects on canine Purkinje fiber

Interrelationships between external potassium concentration and lidocaine: effects on canine Purkinje fiber

Electrical activity in embryonic heart cell aggregates. Pacemaker oscillations.

Aggregates were formed from dissociated heart cells of 7-day chick embryos. When spontaneous action potentials were blocked with 10-8 to 10-7 g/ml tetrodotoxin (TTX) oscillatory pacemaker potentials were sometimes seen. The emergence of these pacemaker potentials was critically dependent on the external potassium concentration. In 1.3 mM potassium medium TTX suppression of action potential generation always led to a stable resting potential close to the threshold level (-55 to -50 mV). In 4.3 mM potassium TTX suppression was followed by a train of pacemaker potentials which usually gave way to a stable resting potential of about -70 mV. Raising the calcium concentration from 1.8 to 5 mM often induced long lasting (3 hrs) pacemaker oscillations of 20 to 30 mV peak to peak amplitude. These were abolished by raising the potassium concentration to 8.3 mM or upon the addition of 1.5 mM Mn2 plus. The responses of TTX-treated aggregates are discussed in terms of Noble and Tsien's pacemaker theory for Purkinje fibers. The results are well described by assuming the existence of an ik2-like potassium current in embryonic heart cells. The role of calcium is unclear but it may help provide the inward current against which the outward potassium current can function.

INFLUENCE OF EXTERNAL POTASSIUM ON THE SYNTHESIS AND DEPOSITION OF MATRIX COMPONENTS BY CHONDROCYTES IN VITRO

The effect of a high external potassium concentration on the synthesis and deposition of matrix components by chondrocytes in cell culture was determined. There is a twofold increase in the amount of chondroitin 4- and 6-sulfate accumulated by chondrocytes grown in medium containing a high potassium concentration. There is also a comparable increase in the production of other sulfated glycosaminoglycans (GAG) including heparan sulfate and uncharacterized glycoprotein components. The twofold greater accumulation of GAG in the high potassium medium is primarily the result of a decrease in their rate of degradation. In spite of this increased accumulation of GAG, the cells in high potassium fail to elaborate appreciable quantities of visible matrix, although they do retain the typical chondrocytic polygonal morphology. Although most of the products are secreted into the culture medium in the high potassium environment, the cell layer retains the same amount of glycosaminoglycan as the control cultures. The inability of chondrocytes grown in high potassium to elaborate the typical hyaline cartilage matrix is not a consequence of an impairment in collagen synthesis, since there is no difference in the total amount of collagen synthesized by high potassium or control cultures. There is, however, a slight increase in the proportion of collagen that is secreted into the medium by chondrocytes in high potassium. Synthesis of the predominant cartilage matrix molecules is not sufficient in itself to ensure that these molecules will be assembled into a hyaline matrix.

Supernormal excitability and conduction in the His-Purkinje system of the dog.

The electrophysiological characteristics of the period of supernormal excitability and supernormal conduction were investigated in the isolated canine His-Purkinje system. Strength-interval curves were determined as the minimum transmembrane current required to bring the impaled fiber to threshold potential following a conducted action potential. During the period of supernormal excitability, 17.0 ± 4.6% (SD) less current than that required during diastole was needed to reexcite fibers throughout the left and right bundle branch-Purkinje system. A period of supernormal excitability was not found in the His bundle proximal to its pseudobifurcation or in ventricular muscle. The period of supernormal excitability was voltage dependent in the bundle branch-Purkinje system; it began during phase 3 at full repolarization (88.8 ± 5.6 [SD] mv) and reached minimum current requirements at about 74.3 ± 5.8 mv. Action potentials evoked during this period were conducted faster than they were during diastole. The maximum rates of depolarization of these supernormally conducted action potentials were not greatly depressed compared with control rates. A period of supernormal conduction was not observed in the His bundle. When the external potassium concentration was increased from 2.7 mM to 5.0 um or 7.5 mM, both the supernormal period of excitability and the period of supernormal conduction were eliminated in Purkinje fibers.

The effects of diphenylthiohydantoin on the membrane potentials of rat sensory nerve fibre bundles

The effect of diphenylthiohydantoin (DPTH) on the membrane of sensory nerve fibre bundles of rats was studied by the sucrose gap method. In normal Locke solution the amplitude of the spike potential and the membrane resistance were increased by DPTH without a concomitant change of the resting potential. The depolarization of the membranes produced by an increase in the external potassium concentration was not influenced by DPTH. Diphenylthiohydantoin partially antagonized the membrane effects of a low concentration of either sodium or calcium, but did not influence the membrane potential when both the sodium and the calcium concentrations were reduced in the suspension medium. It is concluded that DPTH interferes with a sodium-calcium exchange mechanism.

Effects of dieldrin (HEOD) and some of its metabolites on synaptic transmission in the frog motor end-plate

The effects of HEOD and some of its metabolites on synaptic transmission in the frog motor end-plate were studied by means of intracellular microelectrodes. HEOD itself and the metabolites 9- syn-hydroxy-HEOD and the aldrin-derived dicarboxilic acid had no significant effect on frequency and amplitude of miniature end-plate potentials, nor on end-plate membrane potential. In sharp contrast with this aldrin-transdiol (6,7- trans-dihydroxy-dihydro-aldrin) was very potent in exerting both pre- and postsynaptic actions. This metabolite caused a rapid and marked increase in miniature end-plate potential frequency, together with a decrease in their amplitude. Evidence is presented suggesting that the spontaneous transmitter release is enhanced by two prejunctional mechanisms: partly by a calcium-dependent effect, probably a depolarization of the nerve terminal, and partly by a calcium-independent action. Another typical prejunctional action of aldrin-transdiol is the reduction of the amount of transmitter released in response to high external potassium concentration. Aldrin-transdiol also affected the evoked transmitter release and caused a marked increase in end-plate potential amplitude followed by a decrease, and finally a complete blockade of neuromuscular transmission was observed. This transient increase in transmitter release was shown to be due to a transient increase in quantal content. The subsequent fall in end-plate potential amplitude and the fall in miniature end-plate potential amplitude are probably the result of a reduction of the sensitivity of the postsynaptic membrane to acetylcholine as demonstrated by ionophoretic application of this transmitter. There was no aldrin-transdiol-effect on the end-plate membrane potential. The present results strongly support the hypothesis that HEOD must be converted to aldrin-transdiol before it can exert its neurotoxic action.

Excitability changes in crayfish motor neurone terminals.

1. Changes in the post-activation excitability of crayfish motor nerve terminals were used to measure afterpotentials that might be related to facilitation of transmitter release.2. The refractory period is followed by a period of supernormal excitability in which the threshold of nerve terminals drops to about 70% of its pre-activation level at about 15 msec following an impulse. The threshold returns exponentially to its pre-activation level with a time constant of about 25 msec at 13 degrees C. Such a supernormal excitability is rarely seen in pre-terminal nerve branches or in the main axon.3. Following a brief high-frequency tetanus the peak of the supernormal excitability is greater than that following a single impulse. At low temperature this peak is reduced and delayed, and the decay rate of the supernormal excitability is prolonged with a Q(10) of about 2.5.4. Depolarization of nerve terminals decreases, and hyperpolarization increases, the magnitude of the post-activation supernormal excitability.5. The magnitude of the supernormal excitability depends on the external potassium concentration, but not on sodium. In low calcium the peak supernormal excitability is often reduced. High calcium concentration and manganese ions have no effect, but cobalt abolishes the supernormal excitability, and its effects are only slightly reversible. Both cobalt and manganese reversibly block neuromuscular transmission.6. Strophanthidin has no effect on the post-activation supernormal excitability, but proteolytic enzymes reduce or abolish it, and hyperosmotic solutions also affect it.7. It is suggested that the action potential is followed by a depolarizing afterpotential in nerve terminals which is caused by a transient increase in the potassium concentration around the terminals. There is no evidence that afterpotentials in nerve terminals are related to facilitation in any way.

Effect of Gymnodinium breve toxin on potassium influx of erythrocytes

Gymnodin, an ichthyotoxin isolated from cultures of the Florida red-tide organism Gymnodinium breve Davis, was purified by gel filtration chromatography (Sephade LH-20 and chloroform). The effect of gymnodin on potassium influx of rabbit erythrocyte suspensions at 37°C was measured using 42KCl in blood buffer. Relative fluxes (potassium influx for test relative to methanol control) were obtained as a function of the amount of added gymnodin. At the highest concentrations studied (0·4 mg/ml), the relative flux was doubled; with successive dilution of gymnodin, the relative flux decreased and at the lowest dilution studied (10 −5–10 −6) the relative flux was 0·25. A constant concentration of gymnodin (0·4 mg/ml) was used and relative fluxes were determined as a function of the external potassium concentration, [K 0 +] e , over the range 1–10 mM. Two patterns were observed in the diagnostic plot (relative flux vs log 10[K 0 +] e ). The first, a linear increase, was observed for several erythrocytes (human, rabbit and bovine). The second, no variation of flux with external potassium concentration, was observed for genotypically distinct sheep red cells, HK and LK that have high potassium (low sodium) and low potassium (high sodium), respectively.

Electrophysiology of the giant nerve cell bodies of Limnaea stagnalis (L.) (Gastropoda: Pulmonata).

ABSTRACT A mean resting potential of − 53·3 (S.D.± 2·7) mV has been obtained for 23 neurones of the parietal and visceral ganglia of Limnaea stagnalis (L.). Changes in the resting potential of between 28 and 43 mV accompany tenfold changes in [K+0]. A modified constant-field equation accounts for the behaviour of most cells over the range of external potassium concentrations from 0·5 to 10·0 mM/1. Mean values have been estimated for [K+1], 56·2 (S.D.±9·O) mM/1 and PNa/PK, 0·117 (S.D. ±0·028). Investigations on the ionic basis of action potential generation have revealed two cell types which can be distinguished according to the behaviour of their action potentials in sodium-free Ringer. Sodium-sensitive cells are unable to support action potentials for more than 8−10 min in the absence of sodium. Sodium slopes of between 29 and 37 mV per decade change in [Na+0] have been found for these cells. Tetro-dotoxin (5 × 10−5 M) usually blocks action potentials in these neurones. Calcium-free Ringer produces a marked reduction in the overshoot potential and calcium slopes of about 18 mV per decade change in [Ca2+0] are found. Manganous chloride only partially reduces the action potential overshoot in these cells at concentrations of 10 HIM/I. Sodium-insensitive neurones maintain action potentials in the absence of external sodium. Stimulation only slightly reduces the amplitude of the action potential under these conditions and such cells are readily accessible to potassium ions in the bathing medium. A calcium-slope of 29 mV per decade change in [Ca2+0] has been observed in these cells in the absence of external sodium. It is concluded that both sodium and calcium ions can be involved in the generation of the action potential in neurones of Limnaea stagnalis, their relative contribution varying in different cells.