The Effect of Ethanol on the Membrane Permeability to Sodium and Potassium Ions in Frog Muscle Fibres

Toxic myopathies

Toxic myopathies may occur with a variety of prescribed medications, illicit drug abuse, or other toxins. The article discusses an overview of some of the compounds that may cause myopathy, the clinical and laboratory features, histology, mechanisms of action, and potential risk factors of myopathy. The ability to recognize these syndromes is essential to avoid unnecessary tests and to avoid delay in treatment, especially in critically ill patients or patients with other neuromuscular diseases.

Creatine kinase release from isolated EDL muscles in chronic ethanol-treated rats

Chronic ethanol abuse has been shown to cause damage to skeletal muscle in animals and patients as reflected by elevated serum levels of cytosolic enzymes and histological examination. The present study investigated the hypothesis that elevated serum creatine kinase levels in ethanol-treated animals vs. sucrose control animals may result from increased enzyme release or efflux from muscle. Creatine kinase release was measured from extensor digitorum longus (EDL) muscles isolated from rats chronically treated for 28 weeks with ethanol and from sucrose fed controls. The in vitro cumulative release of creatine kinase over a 2-h period was significantly higher in the ethanol-treated animals. Consistent with an increased release of enzyme into the bath, creatine kinase levels in muscle homogenates at the end of the incubation period were lower in the ethanol-treated animals. Creatine kinase levels in serum obtained from trunk blood samples were statistically higher in the ethanol-treated animals compared to sucrose controls. These findings demonstrate increased enzyme release from fast-twitch skeletal muscle in chronic ethanol-treated rats.

Chronic alcohol intake induces reversible disturbances on cellular Na+ metabolism in humans: its relationship with changes in blood pressure

The effect of chronic alcohol consumption on Na(+)-K+ ATPase, Na(+)-Li+ countertransport, outward Na(+)-K(+)-Cl- cotransport system and the Na+ leak was investigated in red blood cells from 18 normotensive subjects with a daily alcohol intake of more than 150 g. The study was repeated after 3 months of alcohol withdrawal, and results were compared with a group of 20 healthy normotensive teetotalers. Maximal efflux rate (Vmax) and apparent dissociation constant for internal Na+ (KNa) of the Na(+)-K+ pump and the Na(+)-Li+ countertransport were significantly higher in alcohol consumers. A positive correlation between daily alcohol intake and Vmax of both transport systems (p less than 0.05) was observed. These values significantly decreased after alcohol withdrawal. A simultaneous stimulation of the Na(+)-K(+)-Cl- cotransport system after alcohol withdrawal was also observed. Blood pressure values were higher in alcoholics (133.7/82.3) than in abstainers (121.4/75 mmHg) and significantly decreased (128.5/76.9 mmHg) after withdrawal. A positive correlation between the stimulation of the Na(+)-K(+)-Cl- cotransport and the decrease of blood pressure after withdrawal was observed. In conclusion, chronic alcohol intake induces disturbances on red blood cell Na+ metabolism that dissipate with the cessation of drinking. Similar abnormalities also reported in humans and animals with primary hypertension have been associated in the pathogenesis of essential hypertension. Therefore, the pressor effect of chronic alcohol intake could be mediated through these changes in cellular Na+ metabolism.

The mode of inhibition of the Na+-K+ pump activity in mast cells by calcium

1 The inhibition by calcium of the Na(+)-K+ pump in the plasma membrane of rat peritoneal mast cells was studied in pure populations of the cells by measuring the ouabain-sensitive uptake of the radioactive potassium analogue, 86rubidium (86Rb+). 2 Exposure of the cells to calcium induced a time- and concentration-dependent decrease in the ouabain-sensitive K+(86Rb+)-uptake of the cells without influencing the ouabain-resistant uptake. The development of the inhibition required the presence of potassium in the medium in the millimolar range (1.5-8.0 mM), and it did not occur at a concentration of potassium (0.24 mM) that is probably rate limiting for the pump activity. In the presence of 1 mM calcium full inhibition developed almost immediately and was not readily reversed. The inhibition was not significantly reduced by 15 min incubation with 1.2 mM EGTA. 3 The inhibitory action of calcium did not develop when the mast cells were incubated in a potassium-free medium, which is known to block Na(+)-K+ pump activity and allow accumulation of sodium inside the cells. Likewise, increasing the sodium permeability of the plasma membrane by monensin abolished the inhibition of the pump activity. In both cases, incubation of the cells with 4.7 mM potassium and tracer amounts of 86Rb+ resulted in a very large uptake of K+ (86Rb+) into the cells (up to 2 nmol per 10(6) cells min-1), indicating a high activity of the Na(+)-K+ pump. 4. These observations support the view that long-term incubation of rat peritoneal mast cells in a calcium-free medium increases the permeability of the plasma membrane to sodium, and the consequent increase in the intracellular concentration of sodium causes an increase in the activity of the pump. Addition of calcium to the cell suspension decreases the sodium permeability, and hence the pump activity. This hypothesis is supported by the stimulation of pump activity produced by monensin, which is not inhibited by calcium. The enhancement of pump activity after exposure of calcium-deprived cells to EGTA might be the result of a further increase in the sodium permeability of the plasma membrane.

[Histochemical study of the skeletal muscle in chronic alcoholism]

Twenty-two chronic alcoholic patients were assessed by neurologic examination and muscle biopsy. The patients manifested proximal muscular weakness to a variable extent. One case presented as an acute bout of myopathy, according to the Manual Muscle Test, MMT. The most prominent histologic feature observed was muscle atrophy (95.3%) better evidenced through the ATPase stain with the predominance of type II A fibers (71.4%). Lack of the mosaic pattern (type grouping) seen in 76% of the cases and an important mitochondrial proliferation with intrasarcoplasmatic lipid accumulation in 63% of the patients. In case of acute presentation of muscle weakness the pathological substrate is quite different, i.e. presence of myositis mainly interstitial characterized by lymphoplasmocytic infiltrate and several spots of necrosis like Zencker degeneration. Based on histologic criteria, our data suggest that: the main determinant of muscle weakness seen in chronic alcoholic patients is neurogenic in origin (alcoholic polyneuropathy); the direct toxic action of ethanol under the skeletal muscle is closely related to the mitochondrial metabolism; the so-called acute alcoholic myopathy has probably viral etiology.

Clinical features, pathogenesis and management of drug-induced rhabdomyolysis

Striated musculature is considered unusually tolerant to all kinds of injuries, and rhabdomyolysis associated with drug overdose or chronic drug intake is a rare event. This may be because striated musculature, in contrast to other tissues such as liver and kidney, shows little affinity for most drugs. Several different types of drug-induced rhabdomyolysis may be distinguished, and the clinical features of the condition may vary widely, from moderate myalgia to involvement of groups of muscles to involvement of the total skeletal musculature. In clinically asymptomatic rhabdomyolysis, early diagnosis is only made if routine laboratory tests include determination of serum creatine kinase. Determination of myoglobin in serum and urine is more sensitive and allows earlier diagnosis of muscle necrosis. Myoglobinaemia may lead to toxin-induced tubular necrosis, and impairment of renal function or even acute renal failure. About 10% of all cases of acute renal failure are due to rhabdomyolysis. Fulminant rhabdomyolysis may be associated with excessive hyperkalaemia and hypocalcaemia which may induce further life-threatening complications. Therefore, early diagnosis of rhabdomyolysis is most important for prevention of its potentially life-threatening sequelae. Therapy of rhabdomyolysis consists of supportive and specific measures. Early diagnosis may help to prevent life-threatening sequelae like acute renal failure, electrolyte imbalance and shock. Withdrawal of the incriminated drug or detoxification in drug overdose should be followed by supportive measures including infusion therapy and correction of dehydration and electrolyte imbalances. Forced diuresis with sodium bicarbonate may protect the kidney function from acidosis and precipitation of myoglobin in tubules. Elimination of myoglobin from plasma may be enhanced by plasmapheresis. In patients with acute renal failure, haemodialysis is necessary. In malignant hyperthermia, immediate infusion of dantrolene sodium is required. This drug also seems to have a beneficial effect in neuroleptic malignant syndrome. The repair mechanisms of striated musculature function extremely well. The prognosis of muscular atrophy after the acute stage of rhabdomyolysis is excellent. The same is true for the prognosis of acute renal failure. However, the extent of complications or survival of the acute stage of rhabdomyolysis strongly depend on early diagnosis and start of adequate therapy.

Disturbances in Na+ transport systems induced by ethanol in human red blood cells

The effects of ethanol on fluxes catalyzed by four Na+ transport systems (ouabain-sensitive Na+, K+ pump, bumetanide-sensitive Na+, K+ cotransport system, Na+:Li+- countertransport and anion carrier) and on Na+ and K+ leaks were investigated in human red blood cells. Ethanol concentrations higher than 32 mM were required in order to significantly modify erythrocyte Na+ transport function. The observed changes can be summarized as follows: (a) stimulation of Na+ efflux through the Na+, K+ pump (by 21-32% at 160-400 mM) and Na+:Li+ countertransport (by 34-59% at 160-400 mM); (b) inhibition of outward Na+, K+ cotransport (by 23-34% at 160-400 mM) and LiCO3- influx through the anion carrier (by 17-21% at 64-400 mM); and (c) increase in Na+ and K+ leaks (by 13-16% at 64-400 mM). The effects of ethanol on the Na+,K+ pump and Na+,K+ cotransport system resulted from changes in maximal rates of Na+ efflux (increased and decreased, respectively) without any significant effect on the apparent affinities for internal Na+. Erythrocytes preincubated for 1 hr with 160 mM ethanol, washed and further incubated in flux media, recovered a normal Na+ transport function. In conclusion, high concentrations of ethanol induced reversible perturbations of fluxes catalyzed by erythrocyte Na+ transport systems. The observed effects may reflect disturbances in Na+ transport function associated with severe intoxication.

The effect of ethanol on spontaneous contractions and on the contraction produced by periarterial nerve stimulation and by acetylcholine in the rat isolated ileum

1. The effect of ethanol (0.01-1000 mg.ml-1) on tone, contractility, and the contractions produced by periarterial nerve stimulation and by acetylcholine was studied in the rat isolated ileum. 2. In low concentrations, ethanol reduced the spontaneous contractions by 60 +/- 1.5% and in high concentrations, it produced a marked contraction in the muscle (3.2 +/- 0.3 g, mean +/- SE, n = 6). 3. In the presence of adrenergic, histaminergic, serotonin and prostaglandin antagonists, ethanol (1.8 mg.ml-1) reduced the contractions produced by periarterial nerve stimulation, at 1-100 Hz with 20 V and 0.2 msec pulse duration, by 80 +/- 3.4%. Ethanol also reduced the contractions produced by acetylcholine (0.001-1 microgram.ml-1), the mean EC50 values were 0.1 +/- 0.01 microgram.ml-1, control, and 0.96 +/- 0.1 microgram.ml-1, in ethanol, respectively. 4. Although the mechanism of action of ethanol at the gut smooth muscle is not clear, it is known that it may block conduction, depolarize the cell membrane and cause release of intracellular calcium, which is, in part, responsible for the contraction produced by ethanol in the rat ileum.

Ethanol effects on voltage-dependent membrane conductances: comparative sensitivity of channel populations in Aplysia neurons

The study of ethanol (EtOH) action is interesting because of its clinical relevance and for the insights it provides into structure-function relationships of excitable membranes. This paper describes the concentration dependencies of various parameters of four currents in Aplysia cells. ICa is the most sensitive of the currents studied. There was a significant reduction of ICa at concentrations of 50 mM EtOH. At low concentrations, the reduction of amplitude was the primary effect of ethanol, with the kinetics and voltage dependency of activation not affected. INa and IA were also affected, but at EtOH levels higher than those which altered ICa. The primary effect of EtOH on INa was a reduction in its amplitude, although the time to peak current flow was increased by EtOH. The effects of EtOH on IA were cell specific and, for the purposes of this paper, we examined the giant metacerebral cell (MCC). In MCC, the primary effect of EtOH on IA was an increase in the time course of inactivation. The time to peak IA was also increased by high concentrations of EtOH, but its amplitude was unaffected even at high concentrations. The delayed rectifier current, IK, was the most EtOH resistant of the currents examined. High EtOH concentrations augmented the amplitude of IK, although even at 600 mM concentrations, the percentage change was only 30%. Our results indicate that the calcium channel is very susceptible to the influence of ethanol and is a serious candidate to be the primary target of EtOH action in the nervous system. The differential sensitivity of voltage-dependent currents and individual components of a given current suggests further experiments to probe the relationship between membrane structure and channel function in excitable membranes.

Effects of low concentrations of ethanol on the embryonic development of Bufo arenarum

The effects of low concentrations of ethanol on embryos of Bufo arenarum were studied. Embryos maintained continuously (from stage 3 on) in 0.84-3.34 microM ethanol showed concentration dependent effects: delay in the development rate and on eclosion, loss of equilibrium, arrhythmic contractions, swimming in atypical positions and high death rate. At lower concentrations the anomalies were concentration independent. Embryos treated continuously with 0.002 and 0.21 microM ethanol until stages 19, 20 and 21 showed an important and selective increase in their Na content. When the embryos were incubated discontinuously in 0.002 and 0.21 microM ethanol, from stage 3 to stages 12-13 and then transferred to Holtfreter solution, only a few of the above mentioned anomalies were observed; they were transient and the embryos recovered rapidly. Treated embryos did not exhibit ultrastructural changes in their ectodermal cells.

General anaesthetics: effects on transmitter release

In this report, the physiological effects, observations and events leading to transmitter release in both central nervous system and peripheral synapses are discussed. The presynaptic modulation of transmission at the central nervous system and at the neuromuscular junction was investigated using electrophysiological and neurochemical techniques. It was concluded that various general anaesthetics may affect the presynaptic mechanism of transmission, but these effects were controversial. For example, terminal excitability, which is taken as an index for presynaptic activity, could either be reduced or increased by general anaesthetics. Similar conflicting effects have been reported for the action of general anaesthetics on spontaneous and evoked release of ACh, uptake and release of intracellular Ca2+, and choline transport into the presynaptic nerve terminals.

The harmful effects of ethanol on ion transport and cellular respiration

The deleterious effects of ethanol on a variety of tissues may result largely from altered ion permeabilities and transport. Clinically relevant ethanol concentrations in blood increase the sodium permeability of the plasma membrane and depress active sodium transport by suppressing Na, K-ATPase activity. As a result, intracellular sodium concentration increases. The total tissue content of calcium increases. Important transport mechanisms deranged by ethanol probably include those regulating calcium-sodium and hydrogen-sodium exchange at the plasma membrane and calcium uptake by the sarcoplasmic reticulum. A modest decline in magnesium content of muscle occurs after chronic exposure to ethanol. This also has been associated with accumulation of calcium. After days to weeks of sustained ethanol intake, sodium pump activity, active sodium transport and tissue oxygen consumption increase. The cell membrane potential, initially lowered by alcohol, increases to supraphysiological levels. This is likely an electrogenic effect of increased sodium transport in response to a sodium leak. Eventually the earlier derangements in tissue composition, including retention of sodium, chloride, and calcium, and reductions in magnesium, potassium, and phosphate, slowly undergo correction. This biphasic response of injury and adaptation appears to depend upon adequate nutrition and the absence of other factors that can adversely affect cell function. That the Na, K-ATPase activity and oxygen consumption remain elevated suggests an ongoing sodium leak of the sarcolemmal membrane. Chronic ethanol-induced cell necrosis may be related to the increased intracellular calcium that accompanies the increase in sodium permeability. Conceivably, critically elevated concentrations of calcium in the cytoplasm may activate autolytic enzymes that in turn may be responsible for structural damage to the cell.

The effects of alcohol on blood pressure and electrolytes

The interaction between alcohol abuse, changes in blood pressure, and electrolyte abnormalities is complex. Some effects of alcohol are seen only with acute ingestion, some during withdrawal, and some only in chronic drinkers. Careful attention to the interactions between the metabolism of various electrolytes can prevent unnecessary morbidity and mortality in alcoholic patients.

Effect of ethanol on stretch response of muscle receptors in cats

The response of muscle spindles and tendon organs to steady and sinusoidal muscle stretch was investigated at different blood alcohol concentrations (BAC). After initial anesthesia (pentobarbital), cats were spinalized, the lumbar ventral roots cut and the gastrocnemius muscles of one hindleg prepared for controlled stretching. The animals were paralyzed and artificial respiration was applied. Action potentials from isolated Ia/Ib/II afferent fibers could be recorded. Under steady stretch conditions, all fibers responded to an increasing BAC with an increase in firing rate. This could be observed already at 0.8 mg/ml BAC. The increase in discharge rate reached at the most 80 imp/s. During intoxication the regularity of firing was higher than in the no-alcohol situation. At blood alcohol concentrations higher than 5 mg/ml, the neuronal activity suddenly dropped to zero, exhibiting an irregular impulse pattern. The increase in discharge rate at steady stretch is regarded to be of minor significance in the explanation of the impairment of motor performance under ethanol. When sinusoidal stretch was applied, the increase in the mean discharge rate was smaller than at steady stretch conditions. Up to about 10 mg/ml BAC the periodical modulation of firing rate during sinusoidal stretch of a large amplitude remained mainly unchanged. After the discharge rate had dropped to zero for the steady stretch condition at high BAC, elicitation of action potentials was always possible using dynamic stretch.

Effects of ethyl alcohol on the directly recorded standing potential of the human eye

The effects of ethanol on the human standing potential (SP) were studied with a recently developed method, which allows direct SP recordings by means of a suction contact lens, temperature stabilized calomel electrodes and d.c. amplification. It is well known that the human SP oscillates with a frequency of about 2/hour in response to a sudden change in illumination. In the present paper marked cyclic variations of the SP, resembling damped oscillations, were provoked by a small oral dose of ethyl alcohol. A first maximum was reached after about 10 min. The difference in amplitude between the peak and the trough of the first oscillation was of the order of 4 mV. The oscillatory frequency was about 2/hour. The length of a cycle varied between 25 and 34 min in different volunteers, being fairly constant in the same subject on different occasions. The SP response to ethanol was similar both under scotopic and photopic conditions. The results correlate well with earlier findings of 2/hour oscillations in c-wave amplitude in response to ethanol, as may be expected considering the partly common origin of the c-wave and the SP.