[Causative factor of Ca2+ transport reduction by sarcoplasmic reticulum fragments under the action of acetylcholine].

The uncoupling of Ca2+ uptake and ATP hydrolysis by acetylcholine (ACh) and choline has been demonstrated on fragmented sarcoplasmic reticulum (FSR) isolated from femoral muscles of Rana ridibunda. The uncoupling depends on the content of oxalate in the incubation medium. An increase in the Ca/ATP ratio caused by serum albumin observed at low oxalate concentrations is indicative of participation of free fatty acids in the uncoupling effect of ACh and choline. The effects of ACh and choline are especially well-pronounced in the case of FSR preparations pretreated with a fatty acid. ACh and choline have no effect on FSR from femoral muscles of Rana temporaria at all oxalate concentrations studied, which may be due to the absence of free fatty acids in these preparations. A pronounced uncoupling effect of ACh is observed after FSR incubation with a fatty acid; the activity of choline is pronounced in a much lesser degree. It is concluded that a decrease in the Ca/ATP ratio in the presence of ACh is due to the enhancement of the uncoupling effects of endogenous free fatty acids.