CALCIUM UPTAKE IN MITOCHONDRIA AND VESICLES OF HEART AND SKELETAL MUSCLE IN PRESENCE OF POTASSIUM SODIUM K-STROPHANTHIN AND PENTOBARBITAL

45Ca++ uptake in mitochondria and vesicles of heart and skeletal muscle was measured in the presence of a low concentration of calcium. The following results were obtained. (1) In mitochondria there was a rapid and brief Ca++ uptake if succinate was present; when ATP was added, Ca++ uptake was slow and prolonged; cyanide prevented the rapid Ca++ accumulation and azide inhibited the slow Ca++ uptake. In vesicles ATP was required for Ca++ uptake and this was increased by oxalate, phosphate, or an ATP regenerating system. (2) k-Strophanthin (10-8-10-4M) had no significant effect on Ca++ uptake in mitochondria or vesicles. (3) Pentobarbital (1-6 mM) inhibited Ca++ uptake in mitochondria of heart and white and red skeletal muscle but had no effect on Ca++ uptake in vesicles. (4) The K+:Na+ ratio in the incubation medium had an effect on Ca++ uptake in mitochondria and vesicles of heart muscle and in mitochondria of red skeletal muscle. In mitochondria Ca++ uptake was minimal at the K+:Na+ ratio of 1, and raising the K+: Na+ ratio up to 10 approximately doubled Ca++ uptake. In vesicles the substitution of Na+ for K+ in the incubation medium diminished Ca++ uptake, if Ca++ uptake was not increased by oxalate, phosphate, or an ATP regenerating system. © 1969.