Mrak R E
Department of Pathology, University of Arkansas for Medical Sciences, Little Rock.
Neurotoxicology. 1989 Fall;10(3):445-54.
Ethanol, in vitro, decreases muscle fiber twitch tension by a mechanism unrelated to the electrical events of the motor end-plate or muscle surface membranes, an effect which may be attributable to a primary ethanol effect on the calcium release process of the sarcoplasmic reticulum. In this study, ethanol was found to progressively decrease a form of calcium release from isolated sarcoplasmic reticulum vesicles seen after calcium loading in high-phosphate media (spontaneous calcium release). Elevated extravesicular free calcium concentrations are known to inhibit spontaneous calcium release, and the ability of sarcoplasmic reticulum to achieve and maintain submicromolar extravesicular free calcium concentrations in the presence of ethanol was therefore determined. Ethanol had no effect on the low extravesicular free calcium concentrations achieved by isolated sarcoplasmic reticulum, and had no effect on residual ATPase activity remaining after cessation of calcium pumping. This latter result suggests that efflux of vesicular calcium and persistent calcium reaccumulation do not occur in the presence of ethanol. These results suggest that ethanol-induced depression of spontaneous calcium release is not attributable to ethanol effects on sarcoplasmic reticulum membrane calcium leakage or on sarcoplasmic reticulum calcium pumping. Ethanol inhibition of spontaneous calcium release from isolated sarcopasmic reticulum may reflect an effect of ethanol on the calcium release process in intact muscle fibers responsible for ethanol-induced decreases in muscle fiber twitch tension.
在体外，乙醇通过一种与运动终板或肌肉表面膜的电活动无关的机制降低肌肉纤维的抽搐张力，这种效应可能归因于乙醇对肌浆网钙释放过程的直接作用。在本研究中，发现乙醇可逐渐降低在高磷酸盐培养基中钙加载后从分离的肌浆网囊泡中观察到的一种钙释放形式（自发钙释放）。已知细胞外游离钙浓度升高会抑制自发钙释放，因此测定了在乙醇存在下肌浆网实现并维持亚微摩尔细胞外游离钙浓度的能力。乙醇对分离的肌浆网所达到的低细胞外游离钙浓度没有影响，对钙泵停止后剩余的残余ATP酶活性也没有影响。后一个结果表明，在乙醇存在下不会发生囊泡钙外流和持续的钙再积累。这些结果表明，乙醇诱导的自发钙释放抑制并非归因于乙醇对肌浆网膜钙泄漏或肌浆网钙泵的影响。乙醇对分离的肌浆网自发钙释放的抑制可能反映了乙醇对完整肌肉纤维中钙释放过程的影响，这一过程导致了乙醇诱导的肌肉纤维抽搐张力降低。
