[Effect of cholesterol on the cooperativeness of the Ca-ATPase of the sarcoplasmic reticulum in rabbit skeletal muscle].

Cooperative properties of Ca-ATPase of the sarcoplasmic reticulum (SR) of rabbit skeletal muscles were examined in health and hypercholesterolemia. As the concentration of ATP was raised (from 50-100 microM to 5 mM) the Hill ratio (Nh) for ATP increased from 0.4 to 3.2. It is assumed that increased cooperative interaction between Ca-ATPase polymers led to a rise in the efficacy of Ca-pump work. Under the conditions described the Nh for UTP increased from 0.43 to 1.0. During hypercholesterolemia (1 g/kg cholesterol for 1, 3 and 6 months), the maximal values of the Nh for ATP did not exceed 2.0, whereas those for UTP 1.0.