Inhalation anaesthetics decrease calcium content of cardiac sarcoplasmic reticulum

In a Langendorff perfused rat heart model, caffeine was shown to have a negative inotropic effect similar to that of inhalation anaesthetics. Both inhalation anaesthetics and caffeine decreased calcium content of left ventricular muscle as measured by atomic absorption spectroscopy. Halothane 2.8% decreased left ventricular pressure by 75.4 (SEM 4.4)% and decreased the calcium content by 30%. Enflurane 5.1% decreased the pressure by 72.4 (6.0)% and decreased calcium content by 31%. Both halothane and enflurane decreased the calcium content of sarcoplasmic reticulum (SR) as measured by caffeine-induced calcium release. There was a high degree of correlation between the negative inotropic effect of inhalation anaesthetics and the decrease in calcium content of the SR (r = 0.95 for halothane, r = 0.91 for enflurane). These data suggest that inhalation anaesthetics increase the calcium permeability of cardiac SR, thereby decreasing the calcium content of SR, resulting in the negative inotropic effect.

Volatile anesthetics decrease calcium content of isolated myocytes

The calcium transient of myocytes was measured using a fluorescent dye, Fura-2. Caffeine, halothane, enflurane, and isoflurane increased the resting calcium level and decreased the calcium transient. The amount of caffeine-induced calcium release was suppressed if myocytes were pretreated with halothane. The amount of halothane-induced calcium release was suppressed if myocytes were pretreated with caffeine. Both halothane and caffeine were found to have similar effects on the sarcoplasmic reticulum (SR). The effect of 4 mM halothane (equivalent to 13.6% v/v) was approximately equivalent to that of 10 mM caffeine. Caffeine, halothane, enflurane, and isoflurane all decreased the total calcium content of myocytes by 10-70%. These data suggest that volatile anesthetics decrease the calcium content of the cardiac SR by increasing the calcium permeability of the SR, and that the mechanism of action of volatile anesthetics may be similar to certain actions of caffeine.

Protection of the heart from ischemia by a new oligomeric derivative of prostaglandin E1

A lipophilic oligomeric ester was synthesized from prostaglandin E1. The compound was found to protect a Langendorff perfused rat heart from ischemic insult. After 15 minutes cessation of perfusion, the flow was restarted, and the recovery of contraction was measured. In control experiments, the recovery was 16.1 +/- 7.3%. In the case of pre-ischemic addition of the compound (10 micrograms/ml at 10 minutes before ischemic insult), the recovery was 31 +/- 13.2% (n = 7; the difference was not significant). In post-ischemic addition (10 micrograms/ml), the recovery was 75.9 +/- 9.0% (n = 7; p less than 0.01). The compound was also effective in protecting rat heart myocytes against a 60 minutes anoxia/15 minutes reoxygenation injury as judged by the loss of "rod-shaped" intact myocytes. At a 10 micrograms/ml concentration, the compound protected against the loss of rod-shaped myocytes by 30% in pre-anoxia addition and 35% in post-anoxia addition. The levels of significance in these experiments were p less than 0.001. Possible mechanisms of action of this compound are discussed.

Prostaglandin derivatives inhibit the growth of malarial parasites in mice

New prostaglandin oligomeric derivatives, termed MR-256 and MR-356, were found to inhibit the growth of murine malarial parasites, P. chabaudi and P. vinckei, within red blood cells in vivo. When mice were infected with P. chabaudi, both MR-256 and MR-356 suppressed the growth of parasites, but MR-356 had a greater inhibitory effect than MR-256. With P. vinckei, MR-356 also inhibited the growth of parasites, and improved the survival rate. The effect of MR-256 was much less. A possible inhibitory mechanism of action of these drugs is discussed.

Interrelationship of brain edema, motor deficits, and memory impairment in rats exposed to focal ischemia

We investigated the relations of brain edema, ion shifts, motor performance, and memory impairment using a focal ischemia model in rats. Cortical infarction was produced by ligation of the middle cerebral artery and the ipsilateral common carotid artery combined with temporary occlusion of the contralateral common carotid artery for 1 hour. Water content and sodium, potassium, and calcium concentrations were measured until Day 14 after the ischemic insult. Significant edema formation was observed; it peaked on Day 3 (p less than 0.001) and then declined. The tissue sodium concentration changed in a manner similar to that of water content, but the tissue potassium concentration changed in an opposite fashion. Massive accumulation of calcium was detected as early as Day 1 after ischemia (almost four times the normal level). The increased calcium concentration was sustained even up to Day 14. Motor performance examinations performed on Day 3, including inclined plane, balance beam, and prehensile tests, demonstrated significantly reduced (p less than 0.001) motor ability that did recover even by Day 7. Passive avoidance learning was carried out on Day 2, followed by a memory retention test on Day 3. Significant memory dysfunction was observed in ischemic compared with sham-operated rats (p less than 0.001). A high correlation coefficient (r = 0.91, p less than 0.01, n = 13) was obtained between water content and calcium concentration on Day 3. Both the total motor score and the degree of disturbance of the passive avoidance reaction also correlated well with water content.

Inhibition of the in vitro formation of dense cells and of irreversibly sickled cells by charybdotoxin, a specific inhibitor of calcium-activated potassium efflux

Charybdotoxin, a specific inhibitor of the calcium-activated potassium channel, was found to inhibit the in vitro formation of irreversibly dehydrated cells and of irreversibly sickled cells, which occur as a result of repeated cycles of sickling and unsickling of sickle red blood cells. The degree of formation of dense cells was measured by Percoll-renografin density gradient centrifugation. 50% inhibition of the formation was achieved at a concentration of 30 nM of charybdotoxin. The approximate half-life of this compound in the circulation of the guinea pig was determined to be 4 h. Charybdotoxin did not inhibit the sickling of sickle cells under deoxygenation. The effects of charybdotoxin in preventing the irreversible changes of sickle cell membranes may be related to the inhibition of calcium-activated potassium efflux in sickle red blood cells.

Protection of rat spinal cord against contusion injury by new prostaglandin derivatives

Two prostaglandin oligomeric compounds, an acid-form compound and an ester-form compound, were synthesized from alprostadil (prostaglandin E1). They were found to provide significant protection to the rat spinal cord against contusion injury. After laminectomy at the T-11 segment of the spinal cord, a weight drop (10 g x 5 cm) caused a "dynamic" injury. The degree of recovery was estimated by several neurologic deficit indices; the Tarlov score, inclined plane test and hot plate test. In the control group (no drug), animals were still paralyzed 4 weeks after injury (Tarlov score 1 to 2). By administering these prostaglandin oligomers, either pre-injury (30 min before injury; one dose of 6 mg/kg i.p.) or post-injury (3 doses, each of 6 mg/kg i.p. at 30 min, 6 h, and 12 h after injury), the Tarlov scores recovered to 3.5 to 4.5 by 4 weeks, and animals were able to either support body weight or to walk with a slight deficit. Although both acid- and ester-forms of the compound demonstrated efficacy, the ester-form provided greater protection to the spinal cord. Other neurologic deficit indices also supported these observations.

Kidneys of chronic alcoholic rats are more vulnerable to ischemic insult

The effects of chronic ethanol ingestion on the rat kidney were studied. Rats were fed a liquid diet containing ethanol for 5 weeks to induce chronic alcoholism. Renal ischemia was introduced by clamping the renal artery and vein either for 10 or 20 min. The glomerular filtration rate (GFR) and the renal blood flow (RBF) were determined by using I125-iothalamate and I131-iodohippurate. In the absence of renal ischemia, there were no significant differences in the renal function between nonalcoholic rats (n = 5) and alcoholic rats (n = 5): 380 +/- 30 vs. 403 +/- 27 microliters/min/100 g body weight (BW) in GFR, and 3.1 +/- 0.1 vs. 3.1 +/- 0.2 ml/min/100 g BW in RBF. The recovery of GFR measured 2 h following 10-min renal ischemia in both groups was not significantly different; the values returned to 340 +/- 40 microliters/min/100 g BW (nonalcoholic rats) and 246 +/- 22 microliters/min/100 g BW (alcoholic rats), respectively. The changes of RBF following 10 min ischemia were also similar in both groups. However, the effects of alcoholism on the renal function became apparent when animals were subjected to more prolonged renal ischemia. In nonalcoholic rats (n = 5), GFR and RBF measured 2 h following 20 min renal ischemia were 245 +/- 51 microliters/min/100 g BW and 2.5 +/- 0.4 ml/min/100 g BW, whereas in alcoholic rats (n = 5) the GFR and RBF were significantly decreased to 93 +/- 15 microliters/min/100 g BW and 1.1 +/- 0.2 ml/min/100 g BW, respectively (p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

A prostaglandin oligomeric derivative inhibits activities of phospholipase and protease: a possible mechanism of membrane protection during ischemia

A prostaglandin oligomeric derivative was synthesized by alkaline treatment of prostaglandin E1. This compound protected the perfused rat heart from global ischemia. This compound was found to inhibit several lipolytic and proteolytic enzymes in vitro. When phospholipase A2 from Naja naja venom was used as an enzyme and phosphatidylcholine was used as a substrate, 50 per cent inhibition was achieved at 50 microM of the prostaglandin derivative. When trypsin and casein were used as enzyme and substrate, 50 per cent inhibition was obtained at 80 microM. A possible mechanism of beneficial effect of this compound in protecting membranes during ischemia is discussed.

Chlorpromazine protects rat spinal cord against contusion injury

The protective effect of chlorpromazine on rat spinal cord injury was investigated using a dynamic impact model. A 10 g weight was dropped 5 cm on an impounder placed on the exposed spinal cord at the T-11 level. Changes in potassium concentration on the epidural surface of the injured spinal cord were measured using a combined impounder-K+ electrode assembly. Recovery of motor performance was estimated using the modified Tarlov score. In the injury control (no treatment) group, the recovery was slow. Animals were still paralyzed 4 weeks after injury and none of them could walk; the Tarlov score was 1.88 +/- 0.78 (S.D.). In contrast, the chlorpromazine-treated group (20 mg/kg i.p. 30 min prior to injury) recovered significantly in 4 weeks. Animals could either support body weight or walk with some deficit; the Tarlov score was 4.0 +/- 0.35. Chlorpromazine inhibited potassium efflux from the spinal cord after contusion. Possible mechanisms of protection of neural cells by chlorpromazine are discussed.

Detection of malignant hyperthermia susceptibility using a spin label technique on red blood cells

Using spin labelled red blood cells and electron paramagnetic resonance spectroscopy (EPR), we observed that halothane 3 mmol litre-1 produced a much greater decrease in the rotational correlation time of red blood cells from individuals who were at risk for malignant hyperthermia (MH), compared with normals. Subsequently we performed blind tests on 14 individuals whose MH susceptibility status had been determined on the basis of in vitro contracture studies. When compared with the results of the in vitro contracture studies, the EPR studies predicted correctly the patients' status in 13 of the 14 individuals.

Halothane induced disorder of red cell membranes of subjects susceptible to malignant hyperthermia

Membrane fluidity of red blood cells drawn from malignant hyperthermic pigs and humans was studied using spin-probes and electron paramagnetic resonance technique. The order parameter and rotational correlation time were determined with 12-doxylstearate and 16-doxylstearate, respectively. It was found that halothane decreased both parameters, but that the decrease of these parameters in subjects susceptible to malignant hyperthermia was much greater than that in normal subjects. The differences were most pronounced at 3 mM halothane. A possibility of using blood for a non-invasive screening for malignant hyperthermia is discussed.

Is Ca2+ -activated potassium efflux involved in the formation of ischemic brain edema?

A possible role of Ca2+ -activated potassium efflux in brain ischemia was studied using a rat focal cortical infarction model. Three days after ischemic insult, tissue contents of water, sodium, potassium and calcium ions were measured. Charybdotoxin, a specific inhibitor of Ca2+ -activated potassium efflux, was found to reduce the formation of ischemic brain edema when a dosage of 0.15 mg/kg was given by i.v. 20-30 min prior to the onset of ischemic insult.

Charybdotoxin improves motor recovery of the rat after spinal cord injury

Charybdotoxin, a highly specific inhibitor of calcium-activated potassium efflux, was found to protect rat spinal cord against dynamic impact injury. In a control (nontreated) group, a weight drop of 10 gram X 5 cm on the T-11 segment of the rat spinal cord paralyzed hindlimbs, and recovery was slow. After 4 weeks, Tarlov scores (a behavioral index) were 1 to 2; the hind legs could not support body weight. In contrast, with animals pretreated 30 minutes prior to the injury by 0.12 mg charybdotoxin/kg (IP), Tarlov scores increased to 3.5-4.5 by three weeks after injury; animals could walk with some deficit. A possible mechanism for the protective effect of this drug is discussed.

Single cell laser light scattering spectroscopy in a flow cell: repeated sickling of sickle red blood cells

We performed dynamic laser light scattering measurements of hemoglobin aggregates in single, sickle erythrocytes. Sickle erythrocytes were attached to the poly-(L-lysine)-coated surface of a flow cell. They were exposed to several oxygenation-deoxygenation cycles by repeatedly changing the flowing solution. The rate of cycling was found to be a determining factor for the formation of irreversible morphologic alterations as well as irreversible hemoglobin aggregates. In slow cycling, the sickle erythrocytes took an irreversible, irregular, rounded shape, and hemoglobin aggregates were observed even in the oxygenated state after 20 cycles. In the fast cycling, however, these changes did not take place even after 60 cycles.

Calcium ionophoretic activity of chemically synthesized oligomeric derivatives of prostaglandin B1

Chemically synthesized dimers, trimers and tetramers of 15-dehydroprostaglandin B1 and 16,16'-dimethyl-15-dehydroprostaglandin B1 facilitate the release of Ca2+ from isolated rat liver mitochondria. The parent monomeric prostaglandins had no significant activity. The rate of release was stimulated by exogenous K+ or Na+, suggesting an antiport exchange of monovalent cations for intra-mitochondrial Ca2+. The activity depended upon the presence of ruthenium red, which prevented recycling of Ca2+; comparison of the activity with A23187 and carbonyl cyanide p-trifluoromethoxyphenylhydrazone indicated that the prostaglandin B1 oligomers were functioning as ionophores and the release of Ca2+ was not caused by an uncoupling of oxidative phosphorylation. The oligomers caused a major decrease in the membrane potential but only when the mitochondria were preloaded with exogenous Ca2+, and even then, the Ca2+ efflux was completed before the membrane potential decreased to less than 90 mV. The oligomeric molecules were able to form supramolecular aggregates in the presence of Ca2+ as detected by light scattering. They extracted Ca2+ into an organic phase, and translocated Ca2+ from one aqueous domain to another across an organic barrier; K+ and Na+ modulated these processes. The prostaglandin B1 derivatives also translocated Rb+ from one aqueous phase to another across an organic barrier when Ca2+ was translocated.

Effects of halothane, caffeine, dantrolene and tetracaine on the calcium permeability of skeletal sarcoplasmic reticulum of malignant hyperthermic pigs

Preparing skeletal sarcoplasmic reticulum from both normal and malignant hyperthermia susceptible pigs, the effects of various drugs on the passive calcium permeability of these sarcoplasmic reticulum preparations were studied. It was found that, in the absence of halothane, the permeability of heavy sarcoplasmic reticulum prepared from malignant hyperthermia susceptible pigs was much higher than that of normal pigs. It was observed that halothane, at concentrations above 10 microM (well below anesthetic concentrations, which are on the order of 1 mM), increased the permeability of sarcoplasmic reticulum. The Hill coefficient of the effect of halothane ranged from 1.96 to 2.25, suggesting that some kind of cooperativity was involved in this reaction. The effects of caffeine were similar to those of halothane. Inhibitors, such as tetracaine and ruthenium red inhibited both the calcium permeability and the halothane-induced increment. The Hill coefficient of the effect of tetracaine was 1.75. The mode of inhibition suggests that tetracaine directly binds with the calcium channel to inhibit the calcium efflux. On the contrary, dantrolene did not affect the calcium permeability of the sarcoplasmic reticulum. However, it inhibited the halothane-induced and caffeine-induced increments of the permeability. The Hill coefficient of inhibition by dantrolene ranged from 2.3 to 3.9, suggesting that several molecules of dantrolene may interact cooperatively with one calcium release channel to inhibit the effect of halothane. These results suggest that dantrolene has a unique inhibitory action, which may be related to its efficacy in ameliorating the syndrome of malignant hyperthermia.

Abnormal membrane properties of the sarcoplasmic reticulum of pigs susceptible to malignant hyperthermia: modes of action of halothane, caffeine, dantrolene, and two other drugs

The role of sarcoplasmic reticulum (SR) in malignant hyperthermia (MH) was studied using the heavy microsomal fraction prepared from semitendinosus muscles of both normal and genetically MH-susceptible pigs. In the presence of ATP, SR was loaded with 70 nmol Ca2+/mg SR protein. Under these conditions, MH-SR demonstrated Ca2+-induced Ca2+ release (Ca-ICaR) and halothane-induced Ca2+ release (halothane-ICaR; halothane concentrations as low as 10 microM). Normal SR did not demonstrate these release phenomena. Dantrolene inhibited the halothane-ICaR, but did not inhibit the Ca-ICaR. Ruthenium red and tetracaine inhibited both types of Ca2+ release. From the measurement of passive Ca2+ efflux, it was shown that dantrolene did not affect the Ca2+ permeability of the SR itself, but suppressed only the halothane-induced increment of the permeability. The membrane order parameter of the SR, as measured by the spin-probe EPR technique, indicated that halothane disordered the lipid bilayer of MH-SR to a greater extent than it did of normal SR. This halothane disordering effect on MH-SR was antagonized by dantrolene. Ruthenium red and tetracaine did not antagonize the halothane disordering effect. These results raise the possibility that halothane could disturb the structure of the lipoprotein complex in MH-SR in such a way that it could open the Ca2+-release channels. The Ca2+ thus released further opens the channel through the Ca-ICaR mechanism in a positive feedback fashion, thus triggering the MH syndrome. The efficacy of dantrolene in ameliorating the MH syndrome might be related to the inhibition of this halothane effect.

Effect of ethanol on tropomyosin in solution and in reconstituted thin filaments

The effects of ethanol at concentrations below 10% on the conformation of tropomyosin, its end-to-end polymerization, its binding to F-actin, and its effects on actomyosin ATPase activity were studied. Ethanol stabilized the tropomyosin conformation by shifting the helix thermal unfolding profile to higher temperatures, and increased the end-to-end polymerization of tropomyosin. Ethanol-induced changes in the excimer fluorescence of pyrene-tropomyosin indicated that its conformation was stabilized by ethanol both free and bound to F-actin. Effects of tropomyosin and tropomyosin-troponin on actomyosin ATPase activity were measured under conditions for which tropomyosin binding to F-actin increases the activity. Under conditions for which the binding of tropomyosin to F-actin is optimum, in the presence of tropomyosin, the actomyosin ATPase activity decreased as the ethanol concentration increased, further indicating that ethanol induces a structural change in the tropomyosin-F-actin complex. Under conditions for which the binding of tropomyosin to F-actin is weak (low salt or high temperature), addition of ethanol increased the ATPase activity due to increased binding of tropomyosin to F-actin. Thus, ethanol appears to modify actomyosin ATPase activity by increasing the binding of tropomyosin to F-actin and affecting the structure of tropomyosin in the tropomyosin-F-actin filament.

The mechanism of in vitro formation of irreversibly sickled cells and modes of action of its inhibitors

When red blood cells from sickle-cell patients were exposed to repeated cycles of deoxygenation and reoxygenation (one cycle was 5 min), dehydration of the cells was observed after several cycles of the sickling-desickling process. These dehydrated cells still maintained a biconcave form after 1 h of such cycling, but they started to take the form of irreversibly sickled cells after several hours. If red cells were simply kept deoxygenated for 16 h, neither dehydrated cells nor irreversibly sickled cells were formed. The formation of dehydrated cells was inhibited either by elimination of Ca2+ from the medium, or by the increase of K+ concentration in the medium. Under conditions in which dehydrated cells were not formed, i.e., deoxygenation incubation (either in the absence or presence of Ca2+) or the deoxygenation-reoxygenation cycling in the absence of Ca2+, 15-25% of cellular K+ leaked out during 4 h of incubation. When dehydrated cells were formed in deoxygenation-reoxygenation cycling in the presence of Ca2+, 40-50% of K+ was lost in 4 h. Two different types of inhibitor were found. The first type includes inhibitors of the Ca2+-activated K+ efflux, such as quinine, quinidine or tetraethylammonium chloride. These compounds suppressed both the K+ efflux and the formation of dehydrated cells. The second type includes calmodulin-interacting drugs. For example, chlorpromazine (20 microM) inhibited the formation of dehydrated cells almost completely, even though it did not inhibit the K+ efflux remarkably. Several other calmodulin-binding drugs were found to inhibit the formation of dehydrated cells similarly, and the potency of these drugs to inhibit the formation seems to be related to the binding affinity of these drugs to calmodulin.

Light-scattering study of depolymerization kinetics of sickle hemoglobin polymers inside single erythrocytes

The time course of intracellular depolymerization of hemoglobin S aggregates is directly observed by using microscope laser light-scattering spectroscopy in single sickle erythrocytes upon slow reoxygenation. From the correlation functions of the light intensity scattered from a single cell, we determine the average diffusion coefficient as well as the fraction of hemoglobin aggregates that have intracellular mobility. The oxygen saturation of the hemoglobin of the same cell is measured by single-cell absorption spectrophotometry. Combining the results obtained with these techniques and information on the cellular morphology, we propose a model for the depolymerization process of hemoglobin inside single erythrocytes as they transform from the fully sickled to the normal biconcave shape upon reoxygenation.

Nitrendipine, nifedipine and verapamil inhibit the in vitro formation of irreversibly sickled cells

Nitrendipine, nifedipine and verapamil inhibit the in vitro formation of irreversibly sickled cells. Using a method of forming both dehydrated cells and irreversibly sickled cells in vitro by repeated cycles of sickling and unsickling, the effects of several drugs in inhibiting the formation of these cells were studied. Drugs known as Ca2+ channel antagonists, such as nitrendipine, nifedipine and verapamil were found to inhibit these reactions. Other types of calcium channel blockers, such as lanthanum and zinc, did not inhibit the formation of these cells. The potency of drugs to inhibit irreversibly sickled cell formation was related to the potency of inhibition of calmodulin-activated phosphodiesterase.

Effect of ethanol on troponin calcium binding

The Chelex resin method was found to be suitable for studying drug effects on Ca2+ binding of proteins. In comparison to conventional dialysis techniques, the Chelex method has the following advantages: Ca2+-EGTA buffer is not necessary, free Ca2+ concentration as low as 10(-9) M can be determined directly, and the reaction is complete in 30 min, thus creating fewer problems with protein denaturation at elevated temperatures. Methods to cope with problems inherent to this assay, such as the excluded volume effect of the resin and protein adsorption by the resin are described. The validity of the method was confirmed by the measurements of Ca2+ binding of troponin in the presence and absence of Mg2+. Using this method, it was demonstrated that ethanol concentration as high as 25% does not influence the Ca2+ binding of troponin.

Action of ADP and ethanol on muscle proteins in vitro

The effects of ADP and ethanol on Ca2+ binding of troponin and the superprecipitation of actomyosin were studied. Ca2+ binding of troponin-tropomyosin complex bound to polystyrene particles (Lytron) was increased by ADP, and this increase was inhibited by ethanol. However, Ca2+ binding of the complex as measured by equilibrium dialysis and by the chelex resin method was not influenced by either ADP or ADP plus ethanol. Ca2+ binding of the thin filament, myosin-ghost myofibrils and myofibrils was also not inhibited. Superprecipitation of actomyosin was augmented in the presence of ADP, and the enhancement was inhibited by ethanol. However, this effect of ADP or ethanol was not observed in the presence of an inhibitor of myokinase, p1, p5-di (adenosine-5') pentaphosphate (Ap5A). In the presence of Ap5A, superprecipitation of actomyosin was enhanced when small amounts of ATP (10 microM) and ADP (100 microM) were added 5 min prior to the addition of 2 mM ATP to start the reaction. The enhancement of superprecipitation of actomyosin by ADP may be caused by nuclei produced by a low concentration of ATP which is produced from ADP by contaminating myokinase activity. These data suggest that ADP and ethanol influence Ca2+ binding of the troponin-tropomyosin complex bound to a solid phase, but their effects on superprecipitation may not necessarily reflect muscle contraction in vivo.

Chronic alcohol ingestion alters the calcium permeability of sarcoplasmic reticulum of rat skeletal muscle

Heavy sarcoplasmic reticulum (SR) was prepared from skeletal muscle of control and chronic alcoholic rats, and the effect of in vitro addition of ethanol on the passive Ca2+ permeability was studied. The SR was loaded with Ca2+ in the absence of ATP. Then efflux was initiated by adding an EGTA solution to decrease the extravesicular Ca2+ concentration. The decrease of Ca2+ content of the SR was measured by an optical method using an encapsulated metallochromic indicator (calcein). The Ca2+ permeability of alcoholic rat SR was higher than that of control rats, especially at low external Ca2+ concentrations (below 1 microM). An in vitro (acute) exposure of SR to ethanol increased the Ca2+ permeability of the SR. However, the degree of increase in alcoholic rat SR was smaller than that in control rat SR.