| Abstract: | The effect of ethanol and other low molecular weight alcohols having an anaesthetic action, on the activity of Ca-ATPase (EC 3.6.1.38) as well as on the Ca2+ uptake and efflux and the functional efficiency of Ca-pump in rabbit skeletal muscle sarcoplasmic reticulum membranes was studied. It was found that some alcohols, especially when taken at low concentrations, specifically stimulate the activity of the Ca-pump and Ca-ATPase. The concentration (C) of the alcohol at which the maximum value of the Ca/ATP ratio is achieved, is well correlated with the value of the partition coefficient (P) for this alcohol in a two-phase water/octanol system. As the concentration of an alcohol rises, it primarily affects the release of Ca2+, but the Ca-pump still functions well and is able to compensate for the Ca2+ leakage up to a certain moment, after which the phospholipid bilayer structure changes crucially, and is beginning the denaturation of Ca-ATPase. Finally the increase in the concentration of either of the alcohols results in a complete loss of the Ca-ATPase activity. The specific effect of alcohols cannot be explained in terms of an unitary mechanism based on fluidity changes in the membrane. It is assumed that at low concentrations certain alcohols (or groups of related alcohols) are able to promote the specific transition of membrane proteins into the active state, whereas at higher concentrations all alcohols provide for the non-functional state of the proteins. |
