The control by internal calcium of membrane permeability to sodium and potassium

Role of external potassium in the calcium-induced potassium efflux from human red blood cell ghosts

The exposure of red cell ghosts to external Ca++ and K+ leads to a rapid net K+ efflux. Preincubation of the ghosts for various lengths of time in the absence of K+ in the external medium prior to a challenge with maximally effective concentrations of Ca++ and K+ renders the ghosts unresponsive to that challenge with a half-time of about 7-10 min. Preincubation at a range of K+ concentrations for a fixed length of time (60 min) prior to the challenge revealed that K+ concentrations of about 500 microM or more suffice to maintain the K+ channel in a maximally responsive state for at least 60 min. These K+ concentrations are considerably lower than the K+ concentrations required to make the responsive channel respond with a maximal rat of K+ efflux. Thus external K+ is not only necessary to induce the permeability change but also to maintain the transport system in a functional state. The presence of Mg++ or ethylenediamine-tetraacetic acid (EDTA) in the K+-free preincubation media preserves the responsiveness to a challenge with Ca++ plus K+. In contrast to external K+, the presence of external Ca++ does not reduce but rather enhances the loss of responsiveness. An excess of EDTA prevents the effects of Ca++ while washes with EDTA after exposure to Ca++ do not reverse them. In red cell ghosts that contain Ca++ buffers, the transition from a responsive to a nonresponsive state incubation in the absence of external K+ is enhanced. The effects of incubation in the presence of Ca++ in K+-free media are reversed; external Ca++ now reduces the rate at which the responsiveness is lost. The loss of responsiveness after incubation in K+-free media prior to a challenge with external K+ and internal Ca++ does also take place when K+-efflux from red cell ghosts is measured by means of 42K+ into media that have the same K+ concentrations as the ghost interior. This confirms that the effects of K+-free incubation are due to the modification of the K+-selective channel rather than to an inhibition of diffusive Cl--efflux.

A study of otoconia of normal mice and shaker mice

Otoconia from the maculae of the utricule and the saccule of normal mice and shaker mice have been examined by means of polarizing microscopy and scanning electron microscopy. X-ray dispersive analysis was used to determine the elements present in the crystals. The otoconia were found to be negative birefringent crystals. They are among the largest crystals found in mammalian tissues, many being 30-50 microns in length and 109-20 microns in diameter. The majority were calcite (calcium carbonate) crystals. Some crystals had a different morphological appearance and contained phosphorus (phosphate compound) as well as calcium. The phosphate content was much less and sometimes absent from utricular otoconia of shaker mice.

Interaction of divalent cations with human red cell cytoskeletons

The binding of Ca2+ to spectrin from human erythrocytes was investigated by equilibrium dialysis, and the binding of Mn2+ by electron paramagnetic resonance. The results led to the conclusion that no binding sites of high affinity (greater than about 10(4) M-1) are present. In the cytoskeletal protein complex isolated from erythrocytes, which (like crude spectrin) contains actin and some other proteins, a set of sites with an association constant of 4 x 10(4) M-1 for Mn2+ is observed. These may be divalent cation binding sites on the actin molecules. Weak interactions of Ca2+ and Mg2+ with spectrin are reflected by self-association of the spectrin heterodimers, which can be followed in the analytical ultracentrifuge and by light-scattering. This self-association is affected by the state of the protein thiol groups. Conditions in which self-association of spectrin occurs have been defined. No aggregation is observed at the Mg2+ activity thought to correspond to that in the cytoplasm.

Effects of tetraethylammonium chloride on contractile, membrane and cable properties of rabbit artery muscle

1. Two types of effects of tetraethylammonium chloride (TEA) have been found in the smooth muscle cells of the rabbit main pulmonary artery. (a) With rapid onset of action TEA depolarizes the cell membrane, increases the membrane resistance, causes anomalous rectification and occasionally spike potentials in response to externally applied depolarizing current pulses and produces tonic contractions. (b) During prolonged (greater than 30 min) incubation in TEA phasic contractions develop progressively and the vascular strips respond to electrical stimulation with synchronized and powerful contractions. 2. There is a linear relationship between log concentration TEA and depolarization over the range of 10-100 mM-TEA. TEA (10 and 30 mM) raises the membrane resistance and decreases the core resistance. The latter effect appeared to develop more slowly than the former. 3. During short exposure to TEA part of the smooth muscle cells respond to depolarizing current pulses with spike potentials of variable amplitude and duration. These spikes are very sensitive to inhibition by verapamil or nickel chloride but are not affected by tetrodotoxin. The amplitude of electrotonic potentials, increased by TEA, is slightly further elevated by verapamil or nickle chloride. 4. TEA (10 mM) increases the mechanical response to low and intermediate potassium concentrations but has no effect on maximal contractions to high potassium. The slope of the line relating log potassium concentration to membrane potential is decreased by TEA. 5. TEA (10 mM) shifts the concentration response curve for the contractile effect of noradrenaline to the left and increases the maximum of noradrenaline-induced contractions. In the presence of TEA, noradrenaline reduces the membrane potential to markedly lower values than under control conditions. 6. It is concluded that the rapidly occurring effects of TEA on the vascular smooth muscle cells of the rabbit main pulmonary artery are a decrease in potassium and an increase in calcium conductance. The latter effect may be related to a blockade of potassium channels; however, we cannot rule out the possibility that TEA affects calcium conductance independent of its presumed action on potassium channels. The slowly developing effects of TEA may be ascribed to the formation of gap junctions and/or (less likely) to an intracellular accumulation of TEA.

A novel effect of cobalt treatment on calcium-dependent responses of the cockroach salivary gland

After incubation in calcium-free solutions containing cobalt, the readmission of calcium caused prolonged but reversible hyperpolarization of acinar cells of cockroach salivary glands and prolonged fluid secretion. It is suggested that cobalt treatment increases the permeability of the acinar cell membrane to calcium.

Release of calcium ions linked to the activation of potassium conductance in a caffeine-treated sympathetic neurone

1. The mechanism of spontaneous and rhythmic hyperpolarizations which occur in bullfrog sympathetic ganglion cells under the effect of caffeine (2--10 mM) were further analysed. 2. Intracellular injection of EGTA blocked generation of caffeine hyperpolarizations (C-hyperpolarizations): this confirmed the previous conclusion (Kuba & Nishi, 1976) that these hyperpolarizations are caused by rhythmic increases in the K+ conductance (GK) of the membrane as a result of rises in free intracellular Ca2+. 3. The amplitude and duration of a C-hyperpolarization induced by an action potential was a function of the time since the previous one; the longer the interval, greater the area. 4. The relationship between the product of the amplitude and duration of a C-hyperpolarization and the preceding interval depended on external Ca2+; when this was low the relationship shifted, so as to indicate an involvement of a Ca2+ accumulating process in the generation mechanism of C-hyperpolarizations. 5. A rapid lowering of temperature triggered the generation of a C-hyperpolarization before appearance of a rhythmic one. There seemed to be no threshold temperature for the effect of such a cold shock; cooling from any temperature within a certain range (10--25 degrees C) by more than a few degrees was effective. 6. The rapid cooling effect was observed even in a Ca2+-free Mg2+ solution. 7. Dantrolene Na increased the interval between rhythmic C-hyperpolarizations or blocked them, but affected less those triggered by an action potential or cold shock. 8. Intracellular injection of Ca2+ triggered the generation of a C-hyperpolarization before the appearance of a rhythmic one. 9. The latency of the generation of an action potential-evoked C-hyperpolarization was dependent on the preceding interval; the shorter the interval, the longer the latency. There was a refractory period for induction of an action potential-induced C-hyperpolarization. 10. The interval between rhythmic C-hyperpolarizations was increased by a small or moderate membrane hyperpolarization (5--20 mV) and decreased by a larger hyperpolarization; the refractory period of an action potential-induced C-hyperpolarization was similarly increased and then decreased by progressive membrane hyperpolarization. 11. These results suggest that rhythmic increases in the GK under the effect of caffeine are due to oscillations of the intracellular Ca2+ concentration and that there may be Ca storage sites in the bullfrog sympathetic ganglion cell which are comparable to the sarcoplasmic reticulum in the skeletal muscle fibre.

Stimulation of monovalent cation fluxes by electron donors in the human red cell membrane

When human red cells are incubated at 37 degrees C with the artificial electron donor system ascorbate + phenazine methosulphate the fluxes of Rb+ (K+) through the cell membrane are increased. The effect of this donor system is much stronger in energy-depleted than in normal cells. The same effects are produced by HS-glutathione, NADH or NADPH loaded into resealed ghosts, but these electron donors were ineffective when added to the incubation medium. The Rb+ (K+) fluxes induced by electron donors resemble closely those induced by an increase of intracellular Ca2+ (Gardos effect). The electron donors require the presence of intracellular Ca2+ to be effective, but at levels that do not stimulate by themselves the fluxes of K+. Flavoenzyme inhibitors (atebrin and chlorpromazine), oligomycin and quinine prevented the effects of both electron donors and Ca2+ alone; antimycin, upcouplers and ethacrynic acid inhibited them partially; ouabain, furosemide, and rotenone had no effect. The results could be explained if the effect of electron donors is to bring about a change in the redox state of some membrane component(s) that makes intracellular Ca2+ more effective to elicit rapid K+ movements. Plasma membrane oxidoreductase activities could be engaged in this change.

Effect of pH on the calcium metabolism of isolated rat kidney cells

The effects of metabolic and respiratory acidosis and alkalosis on cellular calcium metabolism were studied in rat kidney cells dispersed with collagenase. In both types of acidosis, the intracellular pH, total cell calcium, and the cell relative radioactivity after 60 min of labeling are significantly depressed. Kinetic analysis of 45-ca desaturation curves shows that acidosis decreases all three cellular calcium pools and depresses calcium fluxes between the superficial and cytosolic pools and between the cytosolic and mitochondrial pools. In alkalosis the intracellular pH, the total cell calcium, and the cell relative radioactivity are significantly increased. Kinetic studies show that in alkalosis, only the mitochondrial pool is consistently increased. Calcium exchange between the mitochondrial and cytosolic pool is increased in metabolic alkalosis only. These results suggest that hydrogen ion is an important modulator of calcium metabolism, and that the intracellular pH rather than extracellular pH is the critical factor in determining the calcium status of cells during altered acid-base conditions.

Electrical activity of rat myocardial cells in culture: La3+-induced alterations

Intracellular analysis of neonatal rat (1-2 day old) ventricular cells in culture shows that contracting myocardial cells exhibit an array of different patterns of spontaneous electrical activity. Resting membrane potentials varied between -40 mV and -98 mV. Our results indicate that some cultured cells show resting membrane potentials, overshoot, and total spike amplitude values comparable to those normally found in neonatal and adult rat heart. A low ratio of pacemaker (40%) to nonpacemaker cells (60%) and low incidence of hyperpolarizing after-potentials (35%) were found. La3+ application (0.1-4.0 mM) induced progressive cell depolarization, concomitant diminution in discharge frequency, and marked alteration of action potential configuration. A parallel decline in frequency and strength of rhythmic contractions was observed. Abolition of contractility occurred only in association with depolarization and complete disappearance of action potentials. Recovery of electrical and contractile activity followed medium replacement. Our results indicate that La3+ does not act as a specific excitation-contraction (E-C) uncoupler in the cultured cells but has multiple effects upon their normal electrical characteristics.

The effect of ruthenium red and NEM on lithium efflux from human erythrocytes

The lithium pump in intact human erythrocytes which has previously been shown to be repressed following lithium carbonate ingestion by manic-depressive subjects is now shown to be inhibited selectively by N-ethylmaleimide and ruthenium red, both of which are known to inhibit the erythrocyte Ca pump. It is proposed that active lithium efflux is linked to the concurrent operation of the calcium pump.

Osmotic stability of erythrocytes in human muscular dystrophy before and after phospholipase treatment

The stability of washed erythrocytes from patients with muscular dystrophy was determined in hypotonic phosphate buffered sodium chloride. Control cells were more stable than cells from Duchenne and myotonic patients. After pretreatment of the cells with phospholipase from pancreas, snake venom or bee venom in the presence of 14 mmol/l Ca2+, the order of osmotic stability in the 3 groups was not changed. In isotonic phosphate buffered NaCl, however, the erythrocytes of the myotonic patients were much more stable than the cells of the Duchenne and the control group. The lytic process was further studied in control cells with pancreatic phospholipase. 21 +/- 3 (S.E.M.) % of the cells were lysed. This process was (partly) prevented by omitting the phospholipase, by replacement of Na+ by K+ or Li+, by lowering the Ca2+ concentration, by omitting phosphate, by ouabain, by glucose, by ribose, by sucrose, by tetrodotoxin, a Na+-transport inhibitor. Blocking of the Ca2+ transport by La3+ or mersalyl, greatly stimulated the lytic process.

Calcium-induced potassium pathway in sided erythrocyte membrane vesicles

We have characterized the asymmetric effect of Ca2+ on passive K+ permeability in erythrocyte membranes, using inside out and right-side out vesicles. Ca2+, but not Mg2+, can induce an increase in K+ uptake in inside out vesicles. The half-maximal concentration of Ca2+ required to induce the K+ uptake is 0.2 mM, and the permeability increase is not specific for K+. Thus, the Ca2+- induced permeation process in inside out vesicles is changed from that in the energy-depleted intact cell which requires only micromolar concentrations of Ca2+ and is specific for K+. Removal of spectrin had no effect on the vesicle permeability increase due to Ca2+. Studies with N-ethylmaleimide show that the vesicle channel openings is mediated by a protein and passage is controlled by sulfhydryl groups; furthermore, the Ca2+-induced vesicle pathway is distinct from the normal channel for passive K+ leak in the absence of Ca2+. The protein is sensitive to its phospholipid environment since removal of easily accessible phospholipid head groups on the cytoplasmic face of the vesicles inhibits the Ca2+ -stimulated channel opening.

Oscillations of membrane potential in L cells. IV. Role of intracellular Ca2+ in hyperpolarizing excitability

Effects of divalent cations on oscillations of membrane potentials (i.e., spontaneous repetitive hyperpolarizing responses) and on hyperpolarizing responses induced by electrical stimuli as well as on resting potentials were studied in large nondividing L cells. Deprivation of Ca2+ from the external medium inhibited these hyperpolarizing responses accompanying slight depolarization of the resting potential Sr2+ or Mn2+ applied to the external medium in place of Ca2+ was able to substitute for Ca2+ in the generation of hyperpolarizing responses, while Mg2+, Ba2+ or La3+ suppressed hyperpolarizing responses. The addition of A23187 to the bathing medium or intracellular injection of Ca2+, Sr2+, Mn2+ or La3+ induced membrane hyperpolarization. When the external Ca2+, Sr2+ or Mn2+ concentration was increased, the resting potential also hyperpolarized, in a saturating manner. The amplitude of maximum hyperpolarization produced by high external Ca2+ was of the same order of magnitude as those of hyperpolarizing responses and was dependent on the external K+ concentration. In the light of these experimental observations, it was deduced that the K+ conductance increase associated with the hyperpolarizing excitation is the result of an increase in the intracellular concentration of free Ca2+ mainly derived from the external solution.

Evidence for an intracellular calcium store releasable by surface stimuli ifibroblasts (L cells)

A spontaneously occurring or electrically elicited hyperpolarizing activation (HA) in L cells was previously shown to be due to a specific increase in the membrane K+ permeability (Nelson et at. 1972. J. Gen. Physiol. 60:58--71). Intracellular injection of Ca++ elicits an identical hyperpolarizing response which suggests that the increased K+ permeability associated with the HA is mediated by an increase in cytoplasmic Ca++. In zero-Ca, EGTA-containing saline the proportion of cells in which HA's can be evoked decreases, but the amplitude of those HA's that are produced is comparable to that of HA's in normal Ca saline. Co++ does block the HA but only after a period of 2 h or longer; D-600 does not affect the HA. The observations, with others, suggest that the primary source of the Ca mediating the HA response is intracellular. In L cells the endoplasmic reticulum forms morphologically specialized appositions with the surface membrane which resemble structures at the triads of muscle that are thought to mediate coupling between surface membrane electrical activity and contraction via Ca release from the sarcoplasmic reticulum. The similar structures in L cells may mediate coupling between surface membrane electrical, mechanical, or chemical stimuli and the HA response via release of Ca from the endoplasmic reticulum. Surface-coupled release of Ca from intracellular stores might also regulate a number of other intracellular functions in nonmuscle cells.

Ca2+ control of electrolyte permeability in plasma membrane vesicles from cat pancreas

The influence of Ca2+ and other cations on electrolyte permeability has been studied in isolated membrane vesicles from cat pancreas. Ca2+ in the micromolar to millimolar concentration range, as well as Mg2+, Sr2+, Mn2+ and La3+ at a tested concentration 10(-4) M, increased Na+ permeability when applied at the vesicle inside. When added to the vesicle outside, however, they decreased Na+ permeability. Ba2+ was effective from the outside but not from the vesicle inside. When Ca2+ was present at both sides of the membrane, Na+ efflux was not affected as compared to that in the absence of Ca2+. Monovalent cations such as Rb+, Cs+, K+, Tris+ and choline+ decreased Na+ permeability when present at the vesicle outside at a concentration range of 10 to 100 mM. Increasing Na+ concentrations from 10 to 100 mM at the vesicle inside increased Na+ permeability. The temperature dependence of Na+ efflux revealed that the activation energy increased in the lower temperature range (0 to 10 degrees C) when Ca2+ was present at the outside or at both sides, but not when present at the vesicle inside only or in the absence of Ca2+. The results suggest that the Ca2+ outside effect is due to binding of calcium to negatively charged phospholipids with a consequent reduction of both fluidity and Na+ permeability of the membrane. The Ca2+-inside effect most likely involves interaction with proteins with consequent increase in Na+ permeability. The data are consistent with current hypotheses on secretagogue-induced fluid secretion in acinar cells of the pancreas according to which secretagogues elicit NaCl and fluid secretion by liberating Ca2+ from cellular membranes and by stimulating Ca2+ influx into the cell. The increased intracellular Ca2+ concentration in turn increases the contraluminal Na+ permeability which leads to NaCl influx. The luminal sodium pump finally transports Na+ ions into the lumen.

Hyperpolarization in mouse parathyroid cells by low calcium

Intracellular microelectrodes were used to record the resting membrane potential of mouse parathyroid cells in vitro. The mean value of the membrane potential in 2.5 mM calcium was -20 mV. Exposure to low-calcium solutions (1.5 mM) caused rapid hyperpolarization to a mean value of -50 mV. The relationship between extracellular calcium and the membrane potential was sigmoid, and the transition between high and low intracellular potentials occurred between 1.5 mM and 2.25 mM calcium. Magnesium, manganese, and lanthanum reversed the low-calcium hyperpolarization. In 1.5 mM calcium solutions, the relationship between external potassium (greater than 10 mM) and the membrane potential was 46 mV per 10-fold change in extracellular potassium. In 2.5 mM calcium solutions, the resting membrane potential was independent of the external potassium concentration. It is concluded that the resting membrane potential of mouse parathyroid cells is highly sensitive to the extracellular concentration of calcium and calcium-like ions. With the low-calcium secretory stimulus, hyperpolarization is accompanied by the development of strong dependence of the resting membrane potential on extracellular potassium levels.

Endoplasmic reticulum sequesters calcium in the squid giant axon

Axons were loaded with calcium, rapidly frozen, and freeze-substituted. The endoplasmic reticulum, in addition to mitochondria, contained calcium deposits, as indicated by electron probe x-ray microanalysis. Oxalate injected into living axons helped to preserve calcium-containing deposits during preparation for microscopy. It is concluded that the endoplasmic reticulum is a calcium-sequestering compartment in the squid giant axon.

Calcium metabolism in intact isolated thymocytes

Isolated rat thymocytes incubated under proper metabolic conditions extrude Ca2+ previously taken up under metabolically unfavourable conditions. The extrusion can be supported by both respiratory and glycolytic energy but glycolysis seems to be more efficient for this purpose. La3+ (50--200 micron) and the ionophore A 23187 inhibit cell Ca2+ extrusion. Ruthenium Red (1--100 micron) does not influence cell Ca2+ extrusion while it inhibits the in situ mitochondrial cation uptake. All the results are consistent with a cell regulation model of Ca2+ content in which both plasma membrane and mitochondria co-operate, acting in opposite directions, in order to decrease cytosolic Ca2+ concentration. The possibility of Na+-Ca2+ hetero-exchange participation to cell Ca2+ homeostasis regulation is also discussed.

Effect of calcium on the H+/K+ ATPase of hog gastric microsomes

The K+-stimulated, ouabain-insensitive ATPase activity present in vesicles of microsomal fractions from hog gastric mucosa can be demonstrated in fresh preparations by adding Ca2+ (micron range) to the incubation medium. Ca2+ effect is similar but not additive to the effect of gramicidin or freezing. High Ca2+ concentrations (1 mM) produce an inhibitory effect on the K+-stimulated ATPase activity. This effect is not seen in the presence of gramicidin. Calcium increases the magnitude of ATP-driven H+ uptake in vesicles exposed to K+ for periods of time up to 60 min. At longer times of exposure (120 min) the response does not differ from controls. It is concluded that Ca2+ at low concentrations (micron range) enhances the K+ permeability of the vesicular membrane. At higher concentrations (mM range), Ca2+ becomes inhibitory to the K+ permeability. A role for Ca2+ as a second messenger in stimulus-secretion coupling in the parietal cell is discussed.

The role of calcium in the receptor mediated control of potassium permeability in the rat lacrimal gland

1. In the presence of extracellular Ca, adrenaline stimulated a large increase in the rate of K (86Rb) release from rat lacrimal slices, followed by a lower, more sustained rate. 2. In the absence of extracellular Ca, adrenaline elicited only a transient release of 86Rb. 3. The artificial introduction of Ca into the cytosol by the ionophore A-23187 could also initiate the release of 86Rb. 4. In a zero-Ca medium, if either adrenaline or carbachol produced a transient release of 86Rb, the tissue could not respond to the other agonist with a transient release unless Ca was momentarily reintroduced to the medium. 5. If Ca was present in a limiting concentration, the Ca-dependent rate of 86Rb release elicited from a lacrimal slice exposed simultaneously to carbachol and adrenaline was not significantly different from the release seen with carbachol alone. 6. It is concluded that the agonist-induced release of K from the lacrimal gland consists of both a Ca-independent phase which is initiated by the release of a limited pool of Ca, and a Ca-dependent phase which is mediated by the influx of extracellular Ca. 7. It is also concluded that both alpha-adrenergic and muscarinic receptor occupation activate a common, post-receptor mechanism which may be responsible for both phases of K release.

Role of calcium ions in transient inward currents and aftercontractions induced by strophanthidin in cardiac Purkinje fibres

1. Under the influence of strophantidin, Purkinje fibres exhibit transient inward current (TI) which contributes to arrhythmogenic activity. Voltage-clamp experiments were carried out to study the role of Ca ions in this phenomenon. 2. The amplitude of TI varied directly with the extracellular Ca concentration, CaO. Magnesium ions had an antagonistic effect. 3. TI was closely associated with a phasic increase in force ("aftercontraction"). Like TI, the aftercontraction was evoked by a preceding action potential or by the break of a strong depolarizing pulse. 4. TI and the aftercontraction displayed similar wave forms although peak current preceded peak force by 50--100 msec. Both transients were enhanced by increasing the strength or duration of the preceding depolarization pulse. Both events were slowed as the potential level following the pulse was displaced in the negative direction. 5. TI and the aftercontraction could be evoked in the absence of cardiotonic steroids by strongly elevating CaO. 6. Additional experiments were carried out to test the hypothesis the TI reflects an influx of Ca2+ ions. Moninhibited TI but the developed and removal of the inbibition lagged far behind the effects on the slow inward current. 7. TI could be suppressed and eventually inverted by varying the membrane potential in the positive direction. The inversion potential averaged -5mV and was not consistent with a Ca-specific pathway. The aftercontraction was more closely related to the phasic conductance change underlying the current than to thecurrent flow itself. 8. The results are consistent with the idea that an oscillatory release of Ca from an intracellular store is the primary event underlying both the aftercontraction and the conductance change which generates TI. Digitalis intoxication or very high CaO may promote such events by elevating intracellular Ca levels.

Role of calcium in the fade of the potassium release response in the rat parotid gland

1. The 86Rb release response in the parotid due to alpha-adrenergic (epinephrine), muscarinic (carbachol) or peptide (Substance P) receptor activation exhibited 'fade': a return of efflux to control levels despite the continuing presence of agonist. 2. The time course of fade of the response to all three agonists was independent of the concentration of the agonist. 3. After fade was fully developed to one agonist, the response to an agonist acting on a different receptor was either absent or greatly diminished. 4. Removal of carbachol from muscarinic receptors with atropine 10 min prior to Substance P partially restored the ability of Substance P to produce a response. 5. Fade of the response with all three agonists was greatly retarded by the omission of Ca. 6. release of alpha-amylase did not appear to fade following exposure to carbachol or Substance P. 7. It is concluded that the K+ release response may be inactivated with time due to diminution in responsiveness of the K+ channel to an increase in internal Ca2+.

Influence of (DL)-propranolol and Ca2+ on membrane potential and amino acid transport in Ehrlich ascites tumor cells

(1) (DL)-Propranolol and Ca2+ are shown to alter the transmembrane potential difference of Ehrlich ascites tumor cells as measured by means of the cyanine dye, 3,3'-dipropyl-2,2'-thiodicarbocyanine iodide, whose fluorescent intensity changes as a function of membrane potential. (2) The changes in membrane potential elicited by these agents are dependent of the external K+ concentration in a manner which suggest that the potential changes result from a specific increase in the permeability of the plasma membrane to K+. (3) Na+-dependent amino acid transport in the presence of propranolol can be modulated by varying the external K+ concentration (K+o). The initial rate of uptake is stimulated by propranolol at low K+o and inhibited at high K+o. The change in transport rate is nearly directly proportional to the natural logarithm of [K+]o in the presence of propranolol. (4) ATP depletion of the cells by preincubation with rotenone abolishes the changes in fluorescence and amino acid uptake seen with propranolol as a function of K+o. Restoration of cellular ATP with glucose in presence of Ca2+ restores both fluorescence and amino acid transport changes which occur in response to propranolol. (5) The fluorescence changes and amino acid transport changes in response to propranolol are pH dependent, with little effect seen at pH6. (6) It is concluded that the rate of Na+-dependent amino acid uptake is a function of membrane potential and is dependent on the electrochemical potential difference for Na+.

Is the Ca2+-sensitive K+ channel under metabolic control in human red cells?

It is widely known that a rise in internal Ca2+ leads to an increased K+ permeability of human red blood cells [1,2,3]. Binding of Ca2+ to some membrane receptors is required for the opening of the K+ channel [4]. This requirement, however, seems to alter after "ageing" red cells in vitro in acid-citrate-dextrose solutions. Thus, the free Ca2+ concentration producing half-maximal effect on K+ permeability ([Ca2+]K+-50) of 4-weeks stored cells is approx. 2.10(-4) M (calculated from ref. 3 using 50% free Ca2+ according to Schatzmann [5]); nearly ten times lower than that reported for fresh cells [6]. This observation suggests the possibility that the K+ channel may become more sensitive to Ca2+ on cold storage. The experiments described below support this idea.

Effects of norepinephine, calcium, and rate of discharge on 42K movements in canine cardiac Purkinje fibers

We studied the effect of norepinephrine, calcium concentration, and rate of discharge in the presence of different [Ca2+]0 on radioactive potassium movements in cardiac Purkinje fibers. The following results were obtained: (1) norepinephrine increases potassium uptake in quiescent fibers and in fibers driven at constant rate, but more in the latter; (2) norepinephrine also increases potassium uptake in quiescent fibers depolarized at the plateau; (3) increasing [Ca2+]0 increases potassium uptake in fibers driven at constant rate; (4) increasing [Ca2+]0 may decrease K+ uptake in quiescent fibers; (5) increasing [Ca2+]0 decreases the rate of loss of tissue radioactivity in quiescent fibers and increases it in a driven fiber; (6) increasing the driving rate increases potassium uptake in low and high [Ca2+]0; (7) high [Ca2+]0 increases K+ uptake, especially at low rates; (8) norepinephrine is less effective in increasing K+ uptake in the presence of a high [Ca2+]0. We conclude that: (a) norepinephrine increases potassium uptake by different mechanisms; (b) calcium affects potassium movements when it is allowed to enter the cell, presumably by affecting potassium conductance; (c) the effect of an increased rate of discharge on K+ uptake may involve stimulation of active K+ uptake and may include a calcium-dependent component which is largest at high [Ca2+]0 and a slow rate of drive; (d) simultaneous application of two interventions results in a summation that is smallest when one of the mechanisms is already substantially activated.

Internal calcium concentration and potassium permeability in Paramecium

Ca or EGTA was ionophoretically injected into Paramecium tetraurelia to change [Ca]i. Ca decreased the resting membrane resistance and hyperpolarized the membrane. EGTA had the opposite effect. EGTA following TEA, which suppress GK, had little effect on resistance or resting potential. The I-V relation at steady state was studied before and after EGTA injection while the cell bathed in either K- or TEA-solution. The response to inward test pulses after EGTA injection was similar to that after TEA injection. These results show that [Ca]i controls a steady-state K permeability in Paramecium tetraurelia. A prolonged Ca-spike was recorded after EGTA injection. The plateau potentials in various Ca concentrations in a TEA-solution show the Nernst slope (29 mV for tenfold change in [Ca]o). This result suggests that the prolonged depolarization in this condition is due to a Ca current, after suppression of K-permeability and when [Ca]i is low. The difficulty of obtaining quantitative data on the internal Ca, and the difference between the effects of EGTA injection and TEA injection are discussed.

Effects of manganese, calcium, magnesium and lithium on the ouabain-induced seizure

The effects of the intraventricularly administered cations (Mn2+, Ca2+, Mg2+ and Li+) against the seizure induced by ouabain (3 microgram) were investigated. Mn2+, Ca2+ and Mg2+ caused definite sedation and decreased locomotor activity. But Li+ was without significant behavioral effect at the doses applied. Among the cations used, Mn2+, Ca2+ and Mg2+ showed significant anticonvulsive effect on the ouabain-induced seizure. In comparison, on the dose and molar-to-molar basis, the potency of anticonvulsive action was in the following order: Mn2+ greater than Ca2+ greater than Mg2+. On the contrary, the higher dose of Li+ potentiated the ouabain-induced seizure. The importance of the increased Ca2+ level in the extracellular space or the inhibition of Ca2+ uptake as the anticonvulsive effect of Ca2+, Mn2+ and Mg2+ was discussed.

Some electrical properties of the membrane of the barnacle muscle fibers under internal perfusion

Intracellular perfusion technique has been applied to the muscle fibers of the barnacle species, Balanus nubilus. In these fibers, generation and the form of the calcium spike was governed by the frequency of stimulation and intra- and extracellular calcium concentrations. Voltage-clamp experiments showed that the magnitude of the potassium outward current was controlled by the intracellular calcium concentration whose increase, nearly 10(3)-fold, raised the resting membrane conductance and the outward potassium current. On the other hand, application of 10 mM zinc ions inside the muscle fiber had no effect on either the resting potential or the outward potassium current but suppressed the early inward calcium current. Similarly, the inward calcium current was decreased by low concentration of sodium ions in the extracellular fluid only when its ionic strength was made low by substituting sucrose for the sodium salt. Measurement of outward current with the muscle fiber in calcium-free ASW solution and intracellularly perfused with several cationic solutions established the selectivity sequence TEA less than Cs less than Li less than Tris less than Rb less than Na less than K for the potassium channel.

Use of calcium ionophores to determine the effects of intracellular calcium on the action potential of canine cardiac Purkinje fibers

The effects of calcium ionophores X-537A, A23187, and PR-47 on the action potential of canine cardiac Purkinje fibers were studied using standard microelectrode techniques. The ionophores hyperpolarize the membrane potential, eliminate the notch on the action potential plateau, decrease action potential duration, decrease plateau amplitude and duration, decrease spontaneous diastolic depolarization and excitability, and decrease the rate effect on action potential duration. These effects were shown to be independent of catecholamines, membrane-bound calcium, and the patency of the slow inward current channel. The effects of the ionophores depended on the presence of calcium in the external solution. A plausible interpretation of the data is that an ionophore-mediated increase in intracellular calcium shifts the voltage dependence of transmembrane potassium currents to more negative levels.

The effects of zinc on the morphology of sickle red blood cell ghosts as observed by scanning electron microscopy

The objective of these studies is to define the role of zinc in RBC ghost morphology specifically in comparison to the echinocytogenic effects of calcium. Erythrocyte ghosts were prepared from patients with sickle cell anemia, treated with zinc and/or calcium and the resulting cell morphology studied by scanning electron microscopy. Our results showed that zinc consistently and significantly antagonized the echinocytogenic effect of calcium. A simple log linear statistical model was used to evaluate the data and supported this conclusion. We discuss the potential significance of these findings to the effect of zinc treatment on patients with sickle cell anemia.

Intracellular compartmentation of Na+, K+ and Cl- in the Ehrlich ascites tumor cell: correlation with the membrane potential

The intracellular distribution of Na+, K+, Cl- and water has been studied in the Ehrlich ascites tumor cell. Comparison of the ion and water contents of whole cells with those of cells exposed to La3+ and mechanical stress indicated that La3+ treatment results in selective damage to the cell membrane and permits evaluation of cytoplasmic and nuclear ion concentrations. The results show that Na+ is sequestered within the nucleus, while K+ and Cl- are more highly concentrated in the cell cytoplasm. Reduction of the [Na+] of the incubation medium by replacement with K+ results in reduced cytoplasmic [Na+], increased [Cl-] and no change in [K+]. Nuclear concentrations of these ions are virtually insensitive to the cation composition of the medium. Concomitant measurements of the membrane potential were made. The potential in control cells was -13.7 mV. Reduction of [Na+] in the medium caused significant depolarization. The measured potential is describable by the Cl- equilibrium potential and can be accounted for in terms of cation distributions and permeabilities. The energetic implications of the intracellular compartmentation of ions are discussed.

Effects of replacing medium sodium by choline, caesium, or rubidium, on water and ion contents of renal cortical slices

1. Renal cortical slices from rat, rabbit, and guinea-pig were incubated in media in which choline, caesium or rubidium replaced sodium.2. Slices of rabbit and guinea-pig renal cortex incubated in oxygenated choline Ringer decreased in volume initially and did not swell over 3 hr at 25 degrees C. There was a steady loss of potassium. Inhibition of metabolism (N(2) + 1 mM iodoacetamide) caused some swelling. Ouabain, 10 mM, in choline Ringer affected neither loss of potassium nor tissue water content.3. Slices of rat renal cortex similarly incubated in choline Ringer swelled over 3 hr at 25 degrees C whether or not metabolism was inhibited; ouabain (15 mM) affected neither tissue potassium loss nor tissue water content.4. Incubation in choline Ringer containing either 0.2 mMp-chloromercuribenzoic acid, or 1 mM ethacrynic acid increased the tissue water content of guinea-pig renal cortical slices.5. Depletion of cellular potassium (by preliminary incubation in oxygenated potassium-free sodium Ringer with 10 mM ouabain at 30 degrees C) resulted in increased tissue water content when rabbit renal cortical slices were subsequently incubated in oxygenated choline Ringer at 25 degrees C for 3 hr.6. There was no evidence of energy-dependent extrusion of water or ions from either equilibrated rat or rabbit renal cortical slices leached at 0.5 degrees C and then reincubated at 25 degrees C in choline Ringer.7. Rat and guinea-pig renal cortical slices leached at 0.5 degrees C and reincubated at 25 degrees C swelled in rubidium Ringer and in caesium Ringer. There was no evidence of energy-dependent water or ion extrusion when metabolism was restored after leaching in either of these media. Metabolizing rat slices but not guinea-pig slices swelled faster than slices whose metabolism was inhibited.8. These results lend no support to the mechano-chemical hypothesis which ascribes cellular volume regulation to a contractile mechanism squeezing isotonic extracellular fluid from the cells. Instead it is suggested that cellular water content in these experiments reflects the balance between the rate of loss of potassium (and chloride) from the cells and the rate of uptake of extracellular cation (and chloride) into the cells - these rates reflecting both the electrochemical potential gradients of the ions and membrane permeability to them. The implications in relation to the hypothesis of ouabain-insensitive cellular volume regulation are discussed.

Response of chicken intestine to calcium omission on electrical potential and short-circuit

A comparison of the endogenous PD and ISC, galactose transfer PD and ISC, and leucine transfer PD and ISC by rat and chicken intestine in a buffer with and without calcium, was made. The electrical activity in presence or absence of actively transported substrates was altered in the chicken intestine when a calcium-free buffer was used. No significant differences were observed with rat intestine.

Effect of ionophore A23187 upon membrane function and ion movement in human and toad erythrocytes

Addition of 0.1-0.3 micronM A23187, a divalent cation ionophore, to human erythrocytes suspended in a 1.0 mM 45Ca2+ -containing buffer results in a small (approximately two fold) increase in [Ca2+]i, a significant decrease in osmotic fragility, and a decrease in intracellular K+ (100 mmoles/liter of cells to 70 mmoles/liter cells) without significant alteration of intracellular [Na+]. This decrease in [K+]i is associated with a significant decrease in packed cell volume and correlates directly with the observed alteration is osmotic fragility. Increasing extracellular K+ to 125 mM prevents the A23187-induced changes in osmotic fragility, K+ content and cell volume, but does not prevent the ionophore-induced uptake of 45Ca2+. Addition of 0.1-0.3 micronM A23187 to toad erythrocytes leads to an increase in 45Ca2+ uptake comparable to that observed in human erythrocytes, but does not alter osmotic fragility, cell volume or K+ content. Higher concentrations of ionophore (3.0-10.0 micronM) cause a 30- to 50-fold increase in 45Ca2+ uptake and concomitant change in K+ content, cell volume and osmotic fragility. These changes in cell properties can be prevented by increasing extracellular [K+] to 90 mM. The difference in sensitivity of the two cell types to A23187 is attributed to the presence of additional intracellular calcium pools within toad erythrocytes that prevent an increase in cytoplasmic Ca2+ until Ca2+ uptake is increased substantially at the higher concentrations of A23187.

Studies on the cation permeability of human red cell ghosts. Characterization and biological significance of two membrane sites with high affinities for Ca

Net K movements in reconstituted human red cell ghosts and the resealing of ghosts to cations after osmotic hemolysis of red cells have been studied as functions of the free Ca ion concentration. The Ca-dependent specific increase in K permeability was shown to be mediated by a site close to the internal surface of the membrane with an apparent dissociation constant ap pH 7.2 for Ca (K'p1) of 3-5 X 10(-7) M, for Sr of 7 X 10(-6) M. Ba and Mg did not increase the K-permeability of the membrane but inhibited the Ca-mediated permeability changes. K'D1 decreased in a nonlinear fashion when the pH was increased from 6.0 to 8.5. Two different pK' values of this membrane site were found at pH 8.3 and 6.3. The Ca-activated net K efflux into a K-free medium was almost completely inhibited by an increase in intracellular Na from 4 to 70mM. Extracellular K antagonized this Na effect. Changes in the extracellular Na (0.1-140 mM) or K (0.1-6 mM) concentrations had little effect and did not change K'p1. The Ca-stimulated recovery of a low cation permeability in ghost cells appeared to be mediated by a second membrane site which was accessible to divalent cations only during the process of hemolysis in media of low ionic strength. The apparent dissociation constant for Ca at this site (K'p2) varied between 6 X 10(-7) and 4 X 10(-6) M at pH 7.2 Mg, Sr, and Ba could replace Ca functionally. The selectivity sequence was Ca greater than Sr greater than Ba greater than Mg. K'p2 was independent on the pH value in the range between 6.0 and 8.0 Hill coefficients of 2 were observed for the interaction of Ca with both membrane sites suggesting that more than one Ca ion is bound per site. The Hill cofficients were affected neither by the ion composition nor by the Ph values of the intra-and extracellular media. It is concluded that two different pathways for the permeation of cations across the membrane are controlled by membrane sites with high affinities for Ca: One specific for K, one unspecific with respect to cations. The K-specific "channel" has properties similar to the K channel in excitable tissues.

Permeability characteristics of erythrocyte ghosts prepared under isoionic conditions by a glycol-induced osmotic lysis

A detailed study has been made of the permeability characteristics of human erythrocyte ghosts prepared under isoionic conditions by a glycol-induced lysis (Billah, M.M., Finean, J.B., Coleman, R. and Michell, R.H. (1976) Biochim. Biophys. Acta 433, 45-54). Impermeability to large molecules such as dextran (average molecular weight 70 000) was restored immediately and spontaneously after each of the 5-7 lyses that were required to remove all of the haemoglobin. Permeabilities to smaller molecules such as MgATP2-, [3H]inositol and [14C]choline were initially high but could be greatly reduced by incubation at 37 degrees C for an hour. The extent of such resealing decreased as the number of lyses to which the ghosts had been subjected increased. Both removal of haemoglobin and permeabilities to small molecules were affected significantly by pH, CA3+ concentrations and divalent cation chelators. Maximum resealing was achieved in ghosts prepared in the basic ionic medium (130 mM KCl, 10 nM NaCl, 2 mM MgCl2, 10 mM N-2-hydroxyethylpiperazine-N'-2-ethanesulphonic acid (HEPES)) at pH 7.0 (0 degrees C) and with a calcium level around 10(-5) M. Acidic pH facilitated the removal of haemoglobin whilst the presence of divalent cation chelators showed down its release. Retention of K+ by ghosts leaded with K+ during the first lysis and subsequently incubated at 37 degrees C was substantial but lation chelators slowed down its released. Retention of K+ by ghosts loaded with K+ during the first lysis and subsequently incubated at 37 degrees C was substantial but little K+ could be retained within the haemoglobin-free ghosts. Permeability of the ghosts to K+ after one lysis was affected by temperature, pH, Ca2+ concentrations and by the presence of divalent cation chelators.