Studies on calcium transport system in cardiac sarcoplasmic vesicles and its inhibition by dl-propranolol.

Fragmented sarcoplasmic reticulum was prepared from the rabbit heart. The function of vesicles was characterized by the activities of Mg++ and ATP-dependent 'Calcium-Binding' and Ca-ATPase. A fluorescence probe, 1-anilino-8-naphthalene sulfonate (ANS) was employed to examine the physicochemical changes in vesicular membranes. Chlorpromazine, dl-propranolol and lidocaine inhibited Calcium-Binding activity and increased ANS-fluorescence. There was a good correlation between the changes in two parameters. The potency of three drugs on both parameters decreased in the above-mentioned order. These drugs, however, induced no change in the ANS-fluorescence associated by serum albumin or lecithin. The drugs would act presumably at lipid-protein interfaces in vesicles to increase ANS-fluorescence. Both Ca-ATPase and Basic-ATPase were inhibited by dl-propranolol. These results suggest that the inhibitory action of dl-propranolol on the calcium transport system is ascribable to direct physicochemical effects on vesicular membranes.