Low concentrations of fatty acids can inhibit calcium efflux from sarcoplasmic reticulum vesicles

A low concentration of oleic acid (2 μM) can promote calcium uptake by skeletal and cardiac sarcoplasmic reticulum vesicles when the fatty acid is added to an ongoing calcium uptake reaction carried out at pH 6.8 in 120 mM KCl, 5 mM MgATP and 50 mM phosphate. This effect, which occurred when more than 95% of the added oleic acid became associated with the vesicles, is due primarily to marked inhibition of calcium efflux. The ability of low concentrations of free fatty acids to reduce the calcium permeability of these membranes supports the hypothesis that accumulation of lipid substances may influence cardiac function in pathological states such as myocardial ischemia.