Action Potential Duration, Rate of Stimulation, and Intracellular Sodium

In the first section of this short review the change of the cardiac action potential (APD) with the rate of stimulation under physiological conditions is described and mechanistically analyzed. A fast phase of adaptation is mainly caused by changes in gating characteristics of ionic currents, and rapid modulation of the Na⁺/Ca²⁺ exchanger. The slower phase is largely conditioned by incomplete recovery from inactivation of the late Na⁺ current (late I_Na) and changes in ion concentrations of [K⁺]_e, [Na⁺]_i, and [Ca²⁺]_i, which cause secondary changes in the permeation and the gating of ion channels and flux through transporters. In a second section, an analysis is presented of the rate dependence of APD in pathological conditions and its importance in the genesis of arrhythmias in hypertrophy, heart failure, congenital, and acquired LQT syndromes is summarized. The role of the late I_Na, Na⁺, and Ca²⁺ overload is emphasized. Special attention is given to the paradoxical transient lengthening of APD in LQT3 syndrome for the sudden increase in rate in this setting. The third section consists of a short commentary on Na⁺ and Ca²⁺ overload and drugs which block the late I_Na.     

Shortcomings of current models of glucose-induced insulin secretion

Glucose-induced insulin secretion by pancreatic β-cells is generally schematized by a 'consensus model' that involves the following sequence of events: acceleration of glucose metabolism, closure of ATP-sensitive potassium channels (K_ATP channels) in the plasma membrane, depolarization, influx of Ca²⁺ through voltage-dependent calcium channels and a rise in cytosolic-free Ca²⁺ concentration that induces exocytosis of insulin-containing granules. This model adequately depicts the essential triggering pathway but is incomplete. In this article, we first make a case for a model of dual regulation in which a metabolic amplifying pathway is also activated by glucose and augments the secretory response to the triggering Ca²⁺ signal under physiological conditions. We next discuss experimental evidence, largely but not exclusively obtained from β-cells lacking K_ATP channels, which indicates that these channels are not the only possible transducers of glucose effects on the triggering Ca²⁺signal. We finally address the identity of the widely neglected background inward current (Cl⁻ efflux vs. Na⁺ or Ca²⁺ influx through voltage-independent channels) that is necessary to cause β-cell depolarization when glucose closes K_ATP channels. More attention should be paid to the possibility that some components of this background current are influenced by glucose metabolism and have their place in a model of glucose-induced insulin secretion.     

The L-type Ca2+ channel is involved in microvesicle-mediated glutamate exocytosis from rat pinealocytes

Abstract: Pinealocytes, parenchymal cells of the pineal gland, secrete glutamate through microvesicle-mediated exocytosis upon depolarization by KC1 in the presence of Ca²⁺, which is involved in a novel paracrine-like intercellular signal transduction mechanism in neuroendocrine organs. In the present study, we investigated whether or not the L-type Ca²⁺ channel is involved in the microvesicle-mediated glutamate secretion from cultured rat pinealocytes. Nifedipine, a specific antagonist of the L-type Ca²⁺ channel, inhibited the Ca²⁺-dependent glutamate exocytosis by 48% at 20 uM. Other L-type Ca²⁺ channel antagonists, such as nitrendipine, showed similar effects. 1,4-Dihydro-2,6-dimethyl-5-nitro-4[2-(trifluoromethyl)-phenyl]-3-pyridinecarboxylic acid methyl ester (BAY K8644), an agonist of the L-type Ca²⁺ channel, at 1 uM, on the other hand, stimulated the glutamate exocytosis about 1.6-fold. Consistently, these Ca²⁺ channel antagonists inhibited about 50% of the Ca²⁺ uptake, whereas BAY K8644 increased the uptake 5.3-fold. An antibody against the carboxyl-terminal region of the rabbit L-type Ca²⁺ channel recognized polypeptides of pinealocytes with apparent molecular masses of 250 and 270 kDa, respectively, and immunostained the plasma membrane region of the pinealocytes. These results strongly suggested that the entry of Ca²⁺ through L-type Ca²⁺ channel(s), at least in part, triggers microvesicle-mediated glutamate exocytosis in pinealocytes.     

An association between activity of the Na/K-pump and resistance of Schistosoma mansoni towards complement-mediated killing

The Na/K-pump or Na⁺/K⁺-ATPase (EC 3.6.1.37), couples the hydrolysis of ATP to the active transport of Na⁺ and K⁺ ions across the plasma membrane of virtually all animal cells. The relationship between activity of the Na⁺/K⁺-ATPase and the sensitivity of Schistosoma mansoni to immunological attack has been investigated. It has been observed that ouabain, the specific inhibitor of the pump, via a synergistic effect with specific antibody and complement, affects the average membrane potential causing depolarization and death of complement resistant parasites. Thus, apparently, there is association between the inhibition of the Na/K-pump and the lysis and death of the complement-resistant parasite.     

Modulation of Two Cloned Potassium Channels by 1-Alkanols Demonstrates Different Cutoffs

It is not known whether alcohols modulate ion channels by directly binding to the channel protein or by perturbing the surrounding membrane lipid. Cutoff describes the phenomenon where the potency of 1-alkanols monotonically increases with alkyl chain length until a loss of efficacy occurs. Determination of the cutoff for a variety of channels can be important, because similar and/or dissimilar cutoffs might yield information regarding the nature of ethanol's site of action. In this study, the two-electrode voltage clamp technique was used to determine the cutoffs for the 1-alkanol potentiation of cloned Ca²⁺-activated-K⁺ (BK) channels and for the inhibition of cloned Shaw2 K⁺ channels, expressed in Xenopus oocytes. Ethanol, butanol, hexanol, and heptanol reversibly enhanced BK currents, whereas octanol and nonanol had no effect. In contrast, Shaw2 currents were potently inhibited by both octanol and decanol, but not by undecanol. Taken together, data demonstrate that the modulation of K⁺ channels by long chain alcohols is channel-specific. Interestingly, ethanol was a less potent activator of BK currents in the intact oocyte in comparison with its effect on this channel in excised membrane patches. The decrease in potency could not be attributed to an ethanol-dependent change in Ca²⁺ influx through endogenous voltage-gated channels, an effect that would alter the concentration of Ca²⁺ available to activate BK channels.     

Na+/Ca2+ Exchanger Expression and Function in a Rabbit Model of Myocardial Infarction

Introduction: In general, sarcolemmal Na⁺/Ca²⁺ exchanger (NCX) protein and activity is increased in hearts with ventricular dysfunction. However, in a subset of studies, reduced activity of NCX has been reported. Left ventricular dysfunction (LVD) was induced in the rabbit eight weeks after an apical myocardial infarction.
Methods: Using single microelectrode voltage clamp to assess the NCX activity in isolated ventricular cells, a decrease in NCX activity by ∼30% was observed. Immunoblot analysis indicated increased NCX protein levels by ∼20% in the LVD group. The cause of this paradox is unknown. Overexpression of the protein sorcin increased the activity of NCX without affecting NCX protein levels.
Results: Sorcin protein (dimer) levels were significantly lower in the LVD group (0.67 ± 0.05 n = 15, P < 0.05) compared to sham (1.0 ± 0.16, n = 15). Sorcin monomer levels were not significantly different (sham: 1.0 ± 0.26, LVD: 0.83 ± 0.13). Mathematical modeling of NCX suggests that a reduction of NCX activity during diastole to that in LVD could be achieved by holding the diastolic membrane potential at −60 mV instead of −80 mV. Holding E_m at −60 mV decreased NCX-mediated Ca²⁺ efflux rates to values comparable to those seen in LVD and increased SR Ca²⁺ content and peak systolic [Ca²⁺] in sham and LVD cardiomyocytes.
Conclusions: In conclusion, reduced sorcin expression may be linked to the lower NCX activity in the rabbit model of LVD. Reduced NCX activity during diastole increases SR Ca²⁺ content and Ca²⁺ transient amplitude.     

pH-Regulated Na+ Influx into the Mammalian Ventricular Myocyte: The Relative Role of Na+-H+ Exchange and Na+-HCO3− Co-Transport

In the heart, intracellular Na⁺ concentration (Na⁺_i) is a controller of intracellular Ca²⁺ signaling, and hence of key aspects of cell contractility and rhythm. Na⁺_i will be influenced by variation in Na⁺ influx. In the present work, we consider one source of Na⁺ influx, sarcolemmal acid extrusion. Acid extrusion is accomplished by sarcolemmal H⁺ and HCO₃⁻ transporters that import Na⁺ ions while exporting H⁺ or importing HCO₃⁻. The capacity of this system to import Na⁺ is enormous, up to four times the maximum capacity of the Na⁺-K⁺ ATPase to extrude Na⁺ ions from the cell. In this review we consider the role of Na⁺-H⁺ exchange (NHE) and Na⁺-HCO₃⁻co-transport (NBC) in mediating Na⁺ influx into cardiac myocytes. We consider, in particular, the role of NBC, as so little is known about Na⁺ influx through this transporter. We show that both proteins mediate significant Na⁺ influx and that although, in the ventricular myocyte, NBC-mediated Na⁺ influx is less than through NHE, the proportions may be altered under a variety of conditions, including exposure to catecholamines, membrane depolarization, and interference with activity of the enzyme, carbonic anhydrase.     

Energetics of the Na+ Pump in the Heart

Movement of ions across the cell membrane is driven by the free energy released from ATP hydrolysis. Here we will briefly review the chemistry of Na⁺, K⁺-ATPase reaction; we will also review some recent results defining the relationship between the energetic driving force and Na⁺ efflux by the Na⁺ pump in the normal myocardium and then discuss this relationship for pathophysiologic states in the heart.     

Studies of Red-Cell Membrane Function in Heterozygous β Thalassaemia and Other Hypochromic Anaemias

Red-cell membrane function in normal individuals has been compared with that of a group of patients with either heterozygous β thalassaemia, irondeficiency anaemia or sideroblastic anaemia. The metabolic abnormalities in β-thalassaemic red cells were very similar to those observed in other forms of hypochromic anaemia. The hypochromic cells showed a marked increase in osmotic resistance after incubation for 24 hr which was corrected by buffered glucose but not by D-xylose. Maximal inhibition of the Na ⁺ K-⁺ membrane pumps by 10^-4 ouabain and 10^-3 M ethacrynic acid caused a significant increase in osmotic resistance of both normal and thalassaemic cells. The Na⁺ and K⁺ concentrations of 'young' and 'old' thalassaemic cell populations separated by centrifugation did not differ from normal. There was an increased rate of K⁺ flux across the membrane of both thalassaemic and iron-deficient red cells, with a net increase in the rate of K⁺ loss from the cells. The rate of movement of Na⁺ in and out of the cells was normal in all the hypochromic anaemias studied. The rates of glucose utilization and lactate production were increased in normal and thalassaemic 'young' cells but there was no increase in the 'old' populations of thalassaemic cells with increased K⁺ fluxes. ATP levels were normal in all the abnormal cells studied. It is concluded that all the forms of hypochromic anaemia examined are characterized by increased K⁺ fluxes and excessive loss of K⁺ from the cells. The possible relationship between red-cell haemoglobin content and membrane function is discussed.     

Increase in Beating Rate of Cultured Chick Cardiac Myocytes by Ethanol and Inhibition of the Increase by Antiarrhythmic Drugs

Drinking alcohol sometimes causes cardiac arrhythmia, but the precise mechanism remains unknown. To study the mechanism, we investigated the effects of ethanol exposure on the beating rate of cultured chick cardiac myocytes. Primary cultures of cardiac myocytes were prepared from the ventricles of 14-day-old chick embryos and then treated with ethanol which, in the range of 0.3 to 1.5 vol%, increased the beating rate in a dose-dependent manner. Ethanol (0.6 vol%) caused an increase in the beating rate, but disopyramide (5 μ g/ml) and procainamide (10 μ g/ml), Na⁺ and K⁺ channel blockers, inhibited the increase in the beating rate significantly. Neither lidocaine (5 μ g/ml) nor mexiletine (2 μ g/ml), Na⁺ channel blockers, nor calcium antagonist verapamil (5 ng/ml) inhibited the increase. However, tetraethylammonium chloride (ranging from 15 to 30 mmol/1), a K⁺ channel blocker, inhibited the increase. These findings indicate that ethanol increases the beating rate of cultured chick cardiac myocytes via the activation of the K⁺ channel. This experimental model may be useful in studying the effect of ethanol on the K⁺ channel.     

Ouabain-Sensitive and Oligomycin-Sensitive Adenosine-triphosphatase Activities of Normal Human Lymphocytes

S ummary . Homogenates of highly purified normal human lymphocytes contained two different adenosinetriphosphatase (ATPase) activities. One of these activities was present in a supernatant fraction of the lymphocyte homogenates, possibly related to mitochondria. This activity was independent of the presence of monovalent cations, was insensitive to ouabain, but was inhibited by oligomycin and stimulated by 2,4 dinitrophenol. Exchange of Mg⁺⁺ with Ca⁺⁺, or addition of sodium fluoride completely inhibited this ATPase activity. A K_m-value for the substrate ATP was determined to be 0.83 m m . The specific activity of the oligomycin-sensitive, supernatant ATPase was 0.31 ± 0.13 (SD) μmoles P_i per mg protein per 30 min.
The other ATPase activity was activated by Na⁺ and K⁺ and was inhibited by ouabain. This ATPase activity was only found in the pellet fraction after centrifugation, possibly associated with the cell membranes. The specific activity of this ATPase was 0.25 ± 0.09 (SD) μmoles P_i per mg protein per 30 min. The effect of ouabain in various cation combinations of the assay is reported. Optimal ouabain-sensitive ATPase activity was found at 100 m m Na⁺, 15 m m K⁺ and 6 m m Mg⁺⁺.
Only the oligomycin-sensitive ATPase activity increased after short time stimulation of the lymphocytes by phytohaemagglutinin (PHA), and this could be inhibited by puromycin.
The increased ATPase activity of normal lymphocytes caused by the non-specific mitogen PHA suggest the possibility that the increased ATPase activity of lymphocytes from patients with malignant tumours could be due to a stimulation of the lymphocytes by tumour specific antigens in vivo.     

Early afterdepolarizations: mechanism of induction and block. A role for L-type Ca2+ current

Early afterdepolarizations (EADs) are a type of triggered activity found in heart muscle. We used voltage-clamped sheep cardiac Purkinje fibers to examine the mechanism underlying EADs induced near action potential plateau voltages with the Ca2+ current agonist Bay K 8644 and the effect of several interventions known to suppress or enhance these EADs. Bay K 8644 produced an inward shift of the steady-state current-voltage relation near plateau voltages. Tetrodotoxin, lidocaine, verapamil, nitrendipine, and raising [K]o abolish EADs and shift the steady-state current-voltage relations outwardly. Using a two-pulse voltage-clamp protocol, an inward current transient was present at voltages where EADs were induced. The voltage-dependence of availability of the inward current transient and of EAD induction were similar. The time-dependence of recovery from inactivation of the inward current transient and of EAD amplitude were nearly identical. Without recovery of the inward current transient, EADs could not be elicited. The inward current transient was enhanced with Bay K 8644 and blocked by nitrendipine, but was not abolished by tetrodotoxin or replacement of [Na]o with an impermeant cation. These results support a hypothesis that the induction of EADs near action potential plateau voltages requires 1) a conditioning phase controlled by the sum of membrane currents present near the action potential plateau and characterized by lengthening and flattening of the plateau within a voltage range where, 2) recovery from inactivation and reactivation of L-type Ca2+ channels to carry the depolarizing charge can occur. Our results suggest an essential role for the L-type Ca2+ "window" current and provide a framework for understanding the role of several membrane currents in the induction and block of EADs.     

The enzymatic basis for the rat liver 6-hydroxymelatonin sulfotransferase activity

Abstract: Understanding 6-hydroxymelatonin (6HM) sulfation is deemed impor-tant to explaining normal and oncostatic actions of the pineal gland. Here we identify the enzymatic basis for this sulfation in rats. First, a quantitative assay was designed for measuring hepatic 6HM sulfotransferase (6HMST) activity. The as-say was then used to identify a male dominant sexual dimorphism wherein liver from males contains double the 6HMST per g or per 100 g body weight seen in fe-males. Examination of other rat tissues showed that most in vivo 6HM sulfation was likely to occur in liver. In addition, DEAE-Sephadex chromatography of liver cytosol indicated that 80–90% of the 6HMST activity in both sexes was due to an enzyme we named 6HMST II. A minor 6HM sulfotransferase (6HMST I) eluted from the columns prior to the main enzyme. 6HMST II, purified additionally, was shown to convert 6HM to a product that appeared to be 6HM sulfate (6-sulfa-toxymelatonin). The enzyme was inhibited by Na⁺, K⁺, Zn²⁺, and Cd²⁺. Its pH op-timum was 7.80 ± 0.30. Comparisons are made between 6HMST II, dopamine sulfotransferase II, and aryl sulfotransferase IV.     

Demonstration of Central Nervous System Tolerance to Ethanol in Mice: Consequent Effects on Smooth Muscle in Vitro

Mice were given ethanol (9 g/kg) or saline (57 ml/kg) daily in three divided doses for periods of 1 and 4 days to study the effects of such ethanol (ETOH) exposure on central nervous system (CNS) and peripheral smooth muscle (vasa deferentia) function. After 1 day, ETOH-treated mice were functionally tolerant to the hypothermic (3 g/kg, intraperitoneal), but not to the hypnotic (3.25 g/kg, intraperitoneal) effect of ETOH. Functional tolerance to both CNS effects of ETOH was demonstrated in mice after the 4-day ETOH exposure. Norepinephrine (NE) and high K⁺-depolarizing solutions each elicited dose-dependent contractions in the mouse vasa deferens preparation in vitro that consisted of a phasic and tonic component. The tonic components of the NE and K⁺ responses were more dependent upon extracellular Ca²⁺ (Ca²⁺_ext) than the phasic components. Addition of ETOH (120 to 480 mM) or the Ca²⁺ channel-antagonist nifedipine (1× 10+ to 3 × 10⁻-⁷ m) to the preparation selectively inhibited the tonic component of the NE and K⁺ responses, suggesting that both agents acted to inhibit the responses by interfering with the translocation of Ca²⁺_ext. Vasa deferentia isolated from ETOH-treated mice did not exhibit altered reactivity to NE in the phasic or tonic comp nent of the response. The isolated smooth muscle from mice centrally tolerant to ETOH did not appear to be tolerant to the inhibitory effect of ETOH or cross-tolerant to the inhibitory effect of nifedipine on stimulant-induced contractions.     

Acute Ethanol Effects on Focal Cerebral Ischemia in Nonfasted Rats

Focal cerebral ischemia was induced in a rat model of middle cerebral artery occlusion. Three groups of adult male Sprague-Dawley rats, given food and water ad libitum, were subjected to 4 hr of middle cerebral artery occlusion. All were given vehicle control and ethanol pretreatments intraperitoneally 1 hr before. Mean ipsilateral brain water content in the control, 2 g/kg ethanol, and 2 g/kg ethanol + insulin-treated groups showed ischemia core: 81.1%, 82.5%, and 80.9%; intermediate zone: 81.0%. 81.9%, and 80.3%; and outer zone: 80.3%, 81.3%. and 80.1%, respectively. Brain Na⁺ and K⁺ content in these groups paralleled the water content. In addition to significantly ( p < 0.05) more brain edema, the 2 g/kg ethanol-treated animal group also had significant hyperglycemia. In contrast, the 2 g/kg ethanol + insulin-treated animals were normoglycemic and had ischemic, intermediate, and outer zone Na⁺, K⁺, and CI⁻ levels comparable with the control group ( p > 0.05). These results stress the importance of measuring and controlling plasma glucose levels in the in vivo studies of the neurotoxic effects of acute ethanol.     

Protective effect of melatonin on Ca2+ homeostasis and contractility in acute cholecystitis

Abstract:  Impaired Ca²⁺ homeostasis and smooth muscle contractility co-exist in acute cholecystitis (AC) leading to gallbladder dysfunction. There is no pharmacological treatment for this pathological condition. Our aim was to evaluate the effects of melatonin treatment on Ca²⁺ signaling pathways and contractility altered by cholecystitis. [Ca²⁺]_i was determined by epifluorescence microscopy in fura-2 loaded isolated gallbladder smooth muscle cells, and isometric tension was recorded from gallbladder muscle strips. Malondialdehyde (MDA) and reduced glutathione (GSH) contents were determined by spectrophotometry and cycloxygenase-2 (COX-2) expression was quantified by western blot. Melatonin was tested in two experimental groups, one of which underwent common bile duct ligation for 2 days and another that was later de-ligated for 2 days. Inflammation-induced impairment of Ca²⁺ responses to cholecystokinin and caffeine were recovered by melatonin treatment (30 mg/kg). This treatment also ameliorated the detrimental effects of AC on Ca²⁺ influx through both L-type and capacitative Ca²⁺ channels, and it was effective in preserving the pharmacological phenotype of these channels. Despite its effects on Ca²⁺ homeostasis, melatonin did not improve contractility. After de-ligation, Ca²⁺ influx and contractility were still impaired, but both were recovered by melatonin. These effects of melatonin were associated to a reduction of MDA levels, an increase in GSH content and a decrease in COX-2 expression. These findings indicate that melatonin restores Ca²⁺ homeostasis during AC and resolves inflammation. In addition, this indoleamine helps in the subsequent recovery of functionality.     

Bencyclane as an anti-sickling agent

A vasodilating Ca²⁺ channel blocker, bencyclane, was used in 18 patients with homozygous sickle cell anaemia (SCD) to test the possible anti-sickling effect. With bencylane intervention the Na⁺-K⁺ ATPase activity increased from 256±29 to 331±37 nmol Pi/mg protein/h ( P <0.0001) and the Ca²⁺-Mg²⁺ ATPase level increased from 172±12 to 222±44 nmol Pi/mg protein/h ( P <0.0001). The intracytoplasmic Ca²⁺ concentration reduced from 3.5±0.6 to 2.7±0.25 μmol/l ( P <0.0001). The patient's blood contained fewer irreversibly sickled cells (ISCs) (a reduction from 21.4% to 14.4%) ( P <0.05). At the same time MCHC of the erythrocytes decreased from 34.5 to 33.0 g/dl ( P <0.05). Bencyclane appears to be a promising anti-sickling agent that can be used orally in SCD.     

Electrophysiologic Changes in Ischemic Ventricular Myocardium: I. Influence of Ionic, Metabolic, and Energetic Changes

Myocardial Ischemia. Myocardial ischemia leads to significant changes in the intracellular and extracellular ionic milieu, high-energy phosphate compounds, and accumulation of metabolic by-products. Changes are measured in extracellular pH and K⁺ and intracellular pH, Ca²⁺, Na⁺ Mg²⁺, ATP, ADP, and inorganic phosphate. Alterations of membrane currents occur as a consequence of these ionic changes, adrenergic receptor stimulation, and accumulation of lactate, amphipathic compounds, and adenosine. Changes in the volume of the extracellular and intracellular spaces contribute further to the ultimate perturbations of active and passive membrane properties that underlie alterations in excitability, abnormal automaticity, refractoriness, and conduction. These characteristic changes of electrophysiologic properties culminate in loss of excitability and failure of impulse propagation and form the substrate for ventricular arrhythmias mediated through abnormal impulse formation and reentry. The ability to detail the changes in ions, metabolites, and high-energy phosphate compounds in both the extracellular and intracellular spaces and to correlate them directly with the simultaneously occurring electrophysiologic changes have greatly enhanced our understanding of the electrical events that characterize the ischemic process and hold promise for permitting studies aimed at developing interventions that may lessen the lethal consequences of ischemia.     

Effects of Chronic Alcohol Consumption on Enzyme Activities and Active Methionine Absorption in the Small Intestine of Pregnant Rats

The present study evaluates the effect of chronic alcohol intake on the intestinal transport of methionine during pregnancy. For this purpose, we have used an in vitro technique that allows measurement of the unidirectional influx of the amino acids across the brush-border membrane of the rat mid-jejunum, and the basolateral membrane enzyme Na⁺,K⁺-ATPase was also evaluated in the duodenum and jejunum. For chronic alcohol treatment, the rats were fed a liquid diet containing ethanol (36% of calories) or an isocaloric diet (pair-fed control) for 5 weeks before and during pregnancy. Animals were killed at 21 days of gestation. Results from the kinetic analysis revealed that chronic ethanol treatment reduces the maximum transport (J_m) of methionine uptake when compared with controls. Further experiments performed in the presence and absence of sodium have shown that ethanol selectively inhibited Na⁺-dependent methionine transport. At the same time, this treatment significantly reduced the levels of Na⁺,K⁺-ATPase in ethanol-fed rats compared with the controls. Alterations in methionine intestinal transport in pregnant alcohol-fed rats may contribute to the ethanol-induced fetal growth abnormalities.     

Co-ordinated Increase of Sodium Leak and Sodium Pump in Hereditary Spherocytosis

The presence of an increased sodium leak into hereditary spherocytes up to three times normal has been confirmed from measurement of ²²Na⁺ influx into red cells. ²²Na⁺ influx was not identical to the net inward leak of Na⁺ but the two kept a constant relationship since influx was about double the net Na⁺ gain in both normal and abnormal cells incubated with ouabain. The intracellular concentration of Na⁺ ions in fresh cells from hereditary spherocytes was identical to that in normal red cells. Hereditary spherocytes showed increased maximal activity of a membrane ATP-ase inhibited by ouabain and the Na⁺ concentration giving half-maximal activation of this ATP-ase was the same for spherocytes and normal cells. When the ²²Na⁺ influx into red cells from nine patients with hereditary spherocytosis was compared with maximal activity of cation pump ATP-ase in the same cells a significant correlation was obtained ( r = 0.78, P > 0.01). The results indicate some linkage between the increase in the Na⁺ leak and functional number of active cation pumps in the membrane of hereditary spherocytes.