Cation Efflux Research Articles

Poiseuille, Periodicity, and Perfusion: Rhythmic Oscillatory Vasomotion in the Skin

Cutaneous vasomotion has not been actively investigated until recently. This is hardly surprising, as it has not been a reproducible phenomenon. During recent studies on various physiological and pharmacological vascular problems, we identified experimental conditions in which cutaneous vasomotion commonly occurred. We then characterized four methods that routinely provoke human cutaneous vasomotion in vivo, in order to further characterize this physiological phenomenon. Although several adaptive advantages may exist for vasomotion, the most compelling theory can be derived mathematically from Poiseuille's law. Because the flow of a liquid through a vessel is proportional to the fourth power of the radius, it can be demonstrated that the resistance of a vessel with a constant diameter is greater than that of a vessel of the same average diameter in which the diameter changes sinusoidally. Importantly, the rhythmicity originates within the vascular tissue, and there appears to be electromechanical coupling. The cation effluxes demonstrate oscillatory behavior that may be driven by the availability of adenosine triphosphate. Substrate and product concentrations can alter the activity of the allosteric enzyme, phosphofructokinase, which may control the oscillations in ATP concentration. Despite the qualitatively different provocative agents, the cutaneous rhythmic oscillatory vasomotion always first appears after a peak in erythrocyte flux, and it disappears before reaching resting flux levels. Thus, cutaneous rhythmic oscillatory vasomotion is a midrange phenomenon, most likely corresponding to the "oscillatory domain" of glycolysis. Finally, a common feature of tissue preparations for the study of vasomotion is that anesthesia was not used. We have shown that this inhibitory effect of anesthetic agents may persist well beyond "anesthesia," and this suppression may be of clinical importance in the patient with microcirculatory compromise undergoing surgery.

Brush-border TEA transport in intact proximal tubules and isolated membrane vesicles.

The efflux of the organic cation, tetraethylammonium (TEA), across proximal cell luminal membranes was studied using intact, perfused rabbit proximal tubules and isolated rabbit cortical brush-border membrane vesicles (BBMV). Increases of either the extravesicular H+ concentration (from pH 7.5 to pH 6.5) or the extravesicular concentration of unlabeled TEA (from 0.1 to 0.5 mM) increased the rate of efflux of radioactively labeled TEA from BBMV. Similarly, when proximal tubules were preloaded with labeled TEA and then submerged in a mineral oil bath, a rapid increase in either the H+ concentration (from pH 7.5 to pH 5.8) or the TEA concentration (from 0 to 1 mM) of the tubular perfusate produced an acute increase in efflux of the labeled TEA across the luminal brush-border membrane. These results with intact tubules and isolated membranes are consistent with previous suggestions that TEA transport across the brush border of proximal tubule cells involves a carrier-mediated countertransport process and represent the first demonstration with intact proximal tubules that the secretory flux of TEA occurs by an exchange with H+.

Acidification and Ion Permeabilities of Highly Purified Rat Liver Endosomes

While it is well established that acidic pH in endosomes plays a critical role in mediating the orderly traffic of receptors and ligands during endocytosis, little is known about the bioenergetics or regulation of endosome acidification. Using highly enriched fractions of rat liver endosomes prepared by free flow electrophoresis and sucrose density gradient centrifugation, we have analyzed the mechanism of ATP-dependent acidification and ion permeability properties of the endosomal membrane. This procedure permitted the isolation of endosome fractions which were up to 200-fold enriched as indicated by the increased specific activity of ATP-dependent proton transport. Acidification was monitored using hepatocyte and total liver endosomes selectively labeled with pH-sensitive markers of receptor-mediated endocytosis (fluorescein isothiocyanate asialoorosomucoid) or fluid-phase endocytosis (fluorescein isothiocyanate-dextran). In addition, changes in membrane potential accompanying ATP-dependent acidification were directly measured using the voltage-sensitive fluorescent dye Di-S-C3(5). Our results indicate that ATP-dependent acidification of liver endosomes is electrogenic, with proton transport being accompanied by the generation of an interior-positive membrane potential opposing further acidification. The membrane potential can be dissipated by the influx of permeant external anions or efflux of internal alkali cations. Replacement externally of permeable anions with less permeable anions (e.g. replacing Cl- with gluconate) diminished acidification, as did replacement internally of a more permeant cation K+ with less permeant species (such as Na+ or tetramethylammonium). ATP-dependent H+ transport was not coupled to any specific anion or cation, however. The endosomal membrane was found to be extremely permeable to protons, with protons able to leak out almost as fast as they are pumped in. Thus, the internal pH of endosomes is likely to reflect a dynamic equilibrium of protons regulated by the intrinsic ion permeabilities of the endosomal membrane, in addition to the activity of an ATP-driven proton pump.

Plasmid-determined inducible efflux is responsible for resistance to cadmium, zinc, and cobalt in Alcaligenes eutrophus.

In Alcaligenes eutrophus CH34, resistance to chromate is plasmid determined, inducible, and based on decreased net accumulation of the metal anion. Plasmid-encoded resistances to zinc, cadmium, cobalt, and nickel are resulting from inducible, energy-dependent cation efflux systems.

Characterization of Putrescine Production in Nongrowing Vibrio parahaemolyticus Cells in Response to External Osmolality

Nongrowing Vibrio parahaemolyticus cells rapidly produced putrescine (Put) from added arginine when subjected to a low osmotic stress. This phenomenon was characterized in connection with a regulatory mechanism of the responsible enzymes, arginine decarboxylase (ADC) and agmatine ureohydrolase (AUH). NaCl, KCl, LiCl, sucrose, and glycerol were used as solutes to prepare the resuspending media with various osmolalities. Regardless of whether the solutes were electrolytes or non-electrolytes, exposure of cells to low osmolality brought about instantaneous increases in both intra- and extracellular Put contents without significant changes in the contents of other polyamines. This acceleration in Put production was accompanied by no increases in the specific activities of ADC and AUH. On the other hand, when cells were exposed to the osmolality equivalent to 2 or 5% NaCl, all solutes except for glycerol did not cause a remarkable variation in the intracellular Put content, while the amount of Put in the medium varied depending on the solute used; sucrose and glycerol still greatly prompted Put production, as judged by high Put contents in the media, even at the osmolality equivalent to 5% NaCl. The cation efflux from cells, measured as the K+ release, was observed whenever the increase in Put production occurred. Furthermore, in vitro experiments showed that NaCl and KCl inhibited ADC to a similar extent, about 70% inhibition being observed at 200 mM. However, AUH was not affected by these compounds. These results suggest that the reduction in the concentrations of Na+ and K+ predominantly present in cells may cause the increase in activity of the preexisting ADC, which leads to the enhancement of Put production.

A possible role for Na+,K+-ATPase in regulating ATP-dependent endosome acidification.

Endosomes maintain a slightly acidic internal pH, which is directly responsible for their ability to ensure proper sorting of incoming receptors and ligands during endocytosis. At least two distinct subpopulations of endosomes can be distinguished, designated "early" and "late" on the basis of their kinetics of labeling with endocytic tracers. The subpopulations differ not only in their functions (rapid receptor recycling and transport to lysosomes, respectively) but also in their capacities for acidification in intact cells and in vitro. To investigate the possible basis for pH regulation in endosomes, we have studied the transport properties and ion permeabilities of early and late endosomes isolated from Chinese hamster ovary cells. Using endosomes selectively labeled with pH-sensitive endocytic tracers, we found that ATP-dependent acidification is electrogenic, being accompanied by the generation of an interior-positive membrane potential which opposes further acidification. While membrane potential and, consequently, acidification was controlled by the influx of permeant anions and efflux of protons and alkali cations, acidification was further modulated in Na+ and K+-containing buffers by the ouabain- and vanadate-sensitive Na+,K+-ATPase, which appears to be a functional component of the endosomal membrane. The data suggest that electrogenic Na+ transport due to Na+,K+-ATPase activity contributes to the interior-positive membrane potential, thereby reducing ATP-dependent H+ transport. Importantly, inhibition of acidification by Na+,K+-ATPase activity was found only in early endosomes, consistent with their limited acidification capacity relative to late endosomes and lysosomes.

Mechanisms of fusicoccin action: evidence for concerted modulations of secondary K+ transport in a higher plant cell

Fusicoccin (FC) has long been known to promote K(+) uptake in higher plant cells, including stomatal guard cells, yet the precise mechanism behind this enhancement remains uncertain. Membrane hyperpolarization, thought to arise from primary H(+) pumping stimulated in FC, could help drive K(+) uptake, but the extent to which FC stimulates influx and uptake frequently exceeds any reasonable estimates from Constant Field Theory based on changes in the free-running membrane potential (V m) alone; furthermore, unidirectional flux analyses have shown that in the toxin K(+) ((86)Rb(+)) exchange plummets to 10% of the control (G.M. Clint and E.A.C. MacRobbie 1984, J. Exp. Bot.35 180-192). Thus, the activities of specific pathways for K(+) movement across the membrane could be modified in FC. We have explored a role for K(+) channels in mediating these fluxes in guard cells ofVicia faba L. The correspondence between FC-induced changes in chemical ((86)Rb(+)) flux and in electrical current under voltage clamp was followed, using the K(+) channel blocker tetraethylammonium chloride (TEA) to probe tracer and charge movement through K(+)-selective channels. Parallel flux and electrical measurements were carried out when cells showed little evidence of primary pump activity, thus simplifying analyses. Under these conditions, outward-directed K(+) channel current contributed appreciably to charge balance maintainingV m, and adding 10 mM TEA to block the current depolarized (positive-going)V m; TEA also reduced(86)Rb(+) efflux by 68-80%. Following treatments with 10 μM FC, both K(+) channel current and(86)Rb(+) efflux decayed, irreversbly and without apparent lag, to 10%-15% of the controls and with equivalent half-times (approx. 4 min). Fusicoccin also enhanced(86)Rb(+) influx by 13.9-fold, but the influx proved largely insensitive to TEA. Overall, FC promotednet cation uptake in 0.1 mM K(+) (Rb(+)), despite membrane potentials which were 30-60 mVpositive of the K(+) equilibrium potential. These results tentatively link (chemical) cation efflux to charge movement through the K(+) channels. They offer evidence of an energy-coupled mechanism for K(+) uptake in guard cells. Finally, the data reaffirm early suspicions that FC alters profoundly the K(+) transport capacity of the cells, independent of any changes in membrane potential.

Effects of pH, potential, chloride and furosemide on passive Na+ and K+ effluxes from human red blood cells.

Ouabain-resistant effluxes from pretreated cells containing K+/Na+ = 1.5 into K+ and Na+ free media were measured. Furosemide-sensitive cation effluxes from cells with nearly normal membrane potential and pH were lower in NO3- media than in Cl- media; they were reduced when pH was lowered in Cl- media. When the membrane potential was positive inside furosemide increased the effluxes of Na+ and K+ (7 experiments). With inside-positive membrane potential the furosemide-insensitive effluxes were markedly increased, they decreased with decreasing pH at constant internal Cl- and also when internal Cl- was reduced at constant pH. The correlation between cation flux and the membrane potential was different for cells with high or low internal chloride concentrations. The data with chloride greater than or equal to 47 mM showed a better fit with the single-barrier model than with the infinite number-of-barriers model. With low chloride no significant correlation between flux and membrane potential was found. The data are not compatible with pure independent diffusion of Na+ and K+ in the presence of ouabain and furosemide.

Two functionally distinct forms of guanosine cyclic 3',5'-phosphate stimulated cation channels in a bovine rod photoreceptor disk preparation

Cyclic nucleotide stimulated efflux of 22Na+ and 45Ca2+ from a purified bovine rod outer segment disk preparation was measured on the 25-100-ms time scale by a novel rapid superfusion method. Activation of cation efflux by 8-bromoguanosine cyclic 3',5'-phosphate (8-Br-cGMP) was maximal within 25 ms. Over a wide range of concentrations of 8-Br-cGMP, the kinetics of termination of efflux precisely conformed to the sum of two exponential decay processes: a rapid phase (decay constant of 200 ms) and a slower phase (decay constant of 1.6 s). The kinetics of the biphasic decay of efflux cannot be explained by depletion of a pool of releasable 22Na but appear to reflect an intrinsic process for inactivation of the channels. 8-Br-cGMP-stimulated release of actively accumulated 45Ca exhibited identical biphasic decay kinetics. The maximum rate of Ca release [5 nmol.(mg of disk protein)-1.min-1] may be sufficient to produce a 1 microM change in local cytoplasmic [Ca] within 20 ms. The Ca:Na selectivity ratio is approximately 0.5:1 for both decay phases. 8-Br-cGMP demonstrated a lower potency (EC50 of 8.4 microM vs 2.8 microM) but a higher degree of cooperativity in its activation of the rapid vs the slower decay phase of 22Na efflux. The slower phase of decay was selectively inhibited by 25 microM l-cis-diltiazem, a relatively weak inhibitor of the rapid decay phase. Sodium ion (5-10 mM) selectively inhibited the rapid decay phase of 8-Br-cGMP-stimulated 45Ca release. These two kinetically and pharmacologically distinct phases of decay are hypothesized to represent two functionally distinct forms of cGMP-stimulated cation channels.

Influence of amphotericin B on the transport of phosphate, sulphate and potassium ions across the human erythrocyte membrane.

Some effects of the clinically important fungicidal antibiotic amphotericin B on the transport of phosphate, sulphate and potassium ions across the membrane of the human erythrocyte were investigated. In general, amphotericin B inhibited the transport of the anions to about the same degree and stimulated the transport of the cation. At low concentrations, the inhibition of both phosphate and sulphate ion transport was concentration-dependent. A plateau was reached at 47 and 52% transport for phosphate and sulphate, respectively, beyond which no further inhibition was obtained. In contrast, the initial rate of potassium ion release from erythrocytes was stimulated. This effect was also concentration-dependent. The observed stimulatory effect on cation efflux was attributed to penetration of the antibiotic into the membrane of the erythrocyte, leading to the formation of specific channels. The inhibition of transport of anions, however, was attributed to alteration in the fluidity of the lipid bilayer consequent to channel formation.

Nonexclusive solute transport thru protein channels model of the Na,K ATPase complex and similar channels as general transport routes

In earlier work this author put forward a model of the Na,K ATPase complex as a general transport channel. Detailed treatment was limited to anion and monovalent cation transport. Here the functional mechanisms of the Na,K ATPase and similar protein channels as transport routes for all ionic fluxes and also amino acid, sugar and other solutes are presented. Anions, monosaccharide -OH groups and amino acid carboxyls bind to common arginyls and lose hydration water. They combine with cations which bind to adjacent side chain carboxyls, forming neutral ion pairs or positively charged complexes which have minimums in size, hydration and free polar groups. The smaller size and polarity facilitate entry into the tight, structured water channel of some 8–10 A outer bore. Solute fluxes depend on membrane redox activity which maintains channel sulfhydryls in reduced state required for proper transport. ATP binding at channels contributes to transport conformation while ATP hydrolysis gives high efflux of Na +, H + and Ca 2+ as phosphate ion pairs. This cation efflux current clears cations from inner membrane sites, increases negative potential and provides Na + and H + about the outer combining sites, while maintaining their inward gradients. Binding of many agents widens the outer bore to give larger, less selective influx.

A kinetic study of cation transport in erythrocytes from uremic patients

We previously described in red blood cells (RBCs) from uremic patients on dialysis a reduction in sodium (Na) efflux through the Na, potassium (K) cotransport system (Na,K CoT) while Na efflux through the Na,K pump was normal. We then examined Na efflux in fresh cells and in cells loaded to obtain one level of intracellular sodium (Nai) concentration at about 25 mmol/liter cell. In the present study we used similar cation flux methodology to examine the kinetics of cation efflux through the Na,K pump and Na,K CoT in uremic patients on dialysis. RBCs were Na-loaded to attain five different levels of Nai concentration over a range of 5 to 50 mmol/liter cells using the ionophore nystatin. At each level of Na-loading, the Nai achieved was similar in RBCs from controls and patients. Ouabain-sensitive Na efflux through the Na,K pump showed no difference in rate between normals and dialysis patients. When the kinetic parameters of this transport pathway were considered, the apparent affinity (K0.5) for sodium was not significantly different between controls and patients (18.4 +/- 2.3 vs. 20.0 +/- 2.6 mmol/liter cell) and the maximal velocity of efflux (Vmax) was also not different between controls and patients (9.6 +/- 0.7 vs. 8.5 +/- 1.2 mmol/liter cell/hr). Comparison of Nai-activated Na versus K efflux rates through the Na,K CoT in normal subjects demonstrated similar saturation kinetics, (K0.5 15.8 +/- 3.3 vs. 12.2 +/- 2.8 mmol/liter cell, Vmax 0.81 +/- 0.1 vs. 0.78 +/- 0.1 mmol/liter cell/hr) consistent with the known stoichiometric ratio of 1 Na:1 K:2 Cl described for this mechanism.(ABSTRACT TRUNCATED AT 250 WORDS)

The Membrane Potential in a Cytochrome-deficient Species of Bacteroides: Its Magnitude and Mode of Generation

The lipophilic cations butyltriphenylphosphonium (BTPP+), tetraphenylphosphonium (TPP+) and triphenylmethylphosphonium (TPMP+) were taken up into cells of Bacteroides amylophilus H18 under anaerobic conditions. Uptake was dependent on the presence of maltose together with both HCO− 3 and Na+; it was at a maximum at concentrations of ≥ 20 mm-HCO− 3 and ≥2 mm-Na+. The addition of 2-(n-heptyl)-hydroxyquinoline-N-oxide (HpHOQnO) or of an uncoupler of oxidative phosphorylation, or air, resulted in efflux of the lipophilic cations. From the binding behaviour and the physiological effects of the lipophilic cations, a membrane potential (Δψ) of 140 mV was estimated. There was no detectable ΔpH at an external pH of 6·7. The cytoplasmic Na+concentration was estimated to be 0·2 mm, indicating that B. amylophilus can maintain a Na+concentration gradient equivalent to at least 150 mV. Variation in the external Na+concentration (2 to 180 mm) had little influence on Δψ. High external concentrations of the fermentation products acetate, formate and succinate had little effect on the growth rate and the Δψ. The cytoplasmic ATP concentration decreased rapidly on addition of HpHOQnO oxide or of an uncoupler. The maximum internal ATP concentration was only maintained at an external concentration≥2mm-Na+. The NADH: fumarate reductase activity of vesicles of B. amylophilus was associated with alkalization of the suspension medium. The amount of H+taken up was in excess of the expected amount of scalar H+and was partially sensitive to uncoupler. It is concluded that the Δψ was generated via H+translocation driven primarily by the cytochrome-deficient NADH: fumarate reductase system. The transmembrane Na+gradient could be supported via the action of a Na+/2 H+antiporter.

Chloride currents inChara—A patch-clamp study

Ionic current steps were recorded with the patch-clamp technique from algal cells that had been prepared without enzyme treatment. Inward current steps with different conductance levels occurred, the lowest level being 7 pS. There were complex transitions between levels indicating either a lack of independence between single channels, or sublevels of a much larger conductance unit. The reversal potential was consistent with the permeant ion being Cl−. Furthermore, when a different concentration of Cl− was used in the patch electrode the reversal potential of the inward current shifted in a manner consistent with a Nernstian change in the Cl− reversal potential. The frequency of the current steps was voltage dependent and suggestive of the hyperpolarization-activated Cl− currents reported in voltage-clamp studies. Outward current steps, with conductances of 38 pS, were recorded when the membrane patch was depolarized by more than +120 mV. Their amplitude and frequency increased at more positive potentials. The current was probably carried by an efflux of cations through a different set of channels. The resting membrane potential, measured unambiguously without contamination from the tonoplast, was −190±5 mV.

Effects of high hydrostatic pressure on ‘passive’ monovalent cation transport in human red cells

The effects of high hydrostatic pressure (up to 400 ATA) on the 'passive' (defined as ouabain + bumetanide + EGTA-insensitive) influx and efflux of radiotracer cations (K+ Rb+, Na+, Cs+) has been studied in human red cells suspended at different medium tonicities giving altered cell volumes. Under all conditions studied, cation permeability was raised at pressure, and at least two distinct components were found to comprise this flux. Thus, increasing pressure caused a generalized increase in cation permeability which was unaffected by the anion present, demonstrated linear concentration dependence, and was reduced with cell swelling, and stimulated a specific KCl pathway which was Cl- dependent, demonstrated saturation kinetics with raised [K]0 and was increased with cell swelling. High hydrostatic pressure caused a significant alteration to red cell morphology from the normal biconcave disc to cup-shaped forms and it is proposed that this is associated with the unmasking of the volume-sensitive KCl system.

Spatial structures in mitochondrial suspension induced by cation efflux

The formation of spatial structures in a thin unstirred layer of a mitochondrial suspension has been studied. It is shown that the structure formation depends on the state of the ion-transporting systems of mitochondria and that pattern development coincides with the activation of cation efflux from preloaded mitochondria. Spatial structure formation is an energy-dependent process and is suppressed by respiratory chain inhibitors. Patterning is also inhibited by EGTA, EDTA and ruthenium red, reflecting the requirement for divalent cation translocation in mitochondria for the studied phenomenon.

Active extrusion of potassium in the yeast Saccharomyces cerevisiae induced by low concentrations of trifluoperazine.

Trifluoperazine (TFP), the antipsychotic drug, induces substantial K+ efflux, membrane hyperpolarization and inhibition of H+-ATPase in the yeast Saccharomyces cerevisiae. Investigations on the mechanism of these effects revealed two different processes observed at different incubation conditions. At an acidic pH of 4.5 and an alkaline pH of 7.5, K+ efflux was accompanied by substantial proton influx which led to intracellular acidification and dissipation of delta psi formed by cation efflux. The results indicated nonspecific changes in membrane permeability. Similar results were also observed when cells were incubated at pH 5.5-6.0 with higher concentrations of TFP (above 75 microM). On the other hand, low concentrations of TFP (30-50 microM) at pH 5.5-6.0 caused marked membrane hyperpolarization and K+ efflux unaccompanied by the efflux of other cations and by H+ influx. Our experiments indicate that under these conditions K+ efflux was an active process. (1) K+ efflux proceeded only in the presence of a metabolic substrate and was inhibited by metabolic inhibitors. (2) When 0.3-0.9 mM-KCl was present in the medium at pH 6.0, the concentration of K+ within the cells (measured at the end of the incubation with TFP) was much lower than the theoretical concentration of Kin+ if the distribution of K+ between medium and cell water was at equilibrium (at zero electrochemical gradient). (3) Valinomycin decreased the net K+ efflux and decreased the membrane hyperpolarization induced by TFP, probably by increasing the flux of K+ into the cells along its electrochemical gradient. (4) Conditions which led to active K+ efflux also led to a marked decrease in cellular ATP level. The results indicate that under a specific set of conditions TFP induces translocation of K+ against its electrochemical gradient.

Effects of N-ethylmaleimide on ouabain-insensitive cation fluxes in human red cell ghosts

In red cells of several species, the sulfhydryl reagent N-ethylmaleimide activates a Cl −-dependent, ouabain-resistant K + transport pathway. Here we report our attempts to demonstrate ouabain-resistant Cl −-dependent K + fluxes stimulated by N-ethylmaleimide in resealed human red cell ghosts using Rb + as a K + analogue. In contrast to intact cells, the rate constants of the base level Rb + efflux in ghosts were similar in NaNO 3 and NaCl (° k Rb = 0.535 ± 0.079 h −1 and 0.534 ± 0.085 h −1, respectively), while 1 mM N-ethylmaleimide stimulated Rb + efflux strongly in NaNO 3 (° k Rb = 14.26 ± 1.32 h −1) and moderately in NaCl (° k Rb = 2.73 ± 0.54 h −1). This effect was dependent on the presence of internal ATP. Stimulation of Rb + efflux was observed in the presence of ⩾ 0.2 mM N-ethylmaleimide and increased at pH values approaching 8.0, consistent with titration of SH groups. N-Ethylmaleimide-stimulated Rb + efflux was approx. 50% inhibited by 100 μM quinine sulfate whereas 1 μM bumetanide had no effect. In NaCl the N-ethylmaleimide-stimulated efflux saturated with initial internal ghost Rb + concentration, but rates increased linearly in NaNO 3. Replacement of external Na + with glucamine or choline decreased the N-ethylmaleimide-stimulated Rb + efflux, suggesting a role for external Na +. N-Ethylmaleimide-stimulated Rb + efflux was greater in buffers with lipophilic anions such as SCN − or NO 3 − than in solutions with Cl − or acetate. However, the conclude that the effect of N-ethylmaleimide on ouabain-resistant cation effluxes of human red cell ghosts is very different from the selective action of N-ethylmaleimide on Rb + influxes in intact red cells.

Myocardial metabolism: Summary

In planning this session on the in relation to sudden cardiac death , I deliberately chose the title vulnerable myocardium because it is a concept that does not seem to be considered widely. The development of primary ventricular fibrillation may not be so chancey or as unexpected as Dr. James has suggested . If ischemia sets the stage for propagation of inhomogeneous diffusion of conduction, the actors on the stage are the substrates and the electrolytes. There can no longer be any doubt that an energy crisis occurs regionally in the during acute ischemia and , at least theoretically , it should be correctable . Catecholamine-induced peripheral lipolysis can beprofound and , depending on the concentration of stored lipid (mostly in the form of triglyceride and long chain acyl CoA esters) , myocardial lipolysis may also be profound . Glycogenol ysis may be poor in diseased tissue, and glycolysis not sustained or depressed . Fundamental metabolic changes like these must alter the regulation of oxidative phosphorylation which influences, among other things, membrane integrity and, in its tum, the efflux and influx of cation s. There are problems in the study of the myocardium, and these relate to the artificiality of models of

The effect of the energy state of mitochondria on the kinetics of unidirectional cation fluxes

Unidirectional fluxes of triphenylmethylphosphonium and of Cs + as its valinomycin complex were studied using trace concentrations of the cations. The rate constants of influx and efflux were estimated mainly at 0 °C from the uptake kinetics in respiring mitochondria and the in/out ratios in the steady state. The efflux rate constants in the energized state were also measured after dilution of the mitochondrial suspension in the steady state, and in deenergized mitochondria from the efflux rates of cations after inhibition of respiration. It was found that the energy state of mitochondria had little effect on the rate constants of efflux, while the rate of influx was strongly stimulated by respiration. The former finding is not readily explained by the classical chemiosmotic theory, since a transmembrane potential, negative on the inside, formed on energization would be expected to strongly inhibit the efflux of cations. The data may be explained by a pump-and-leak model in which localized electrical fields in hydrophobic domains of the membrane are coupled to the pumping of hydrophobic cations against an electrochemical gradient, while leaks would effect efflux.