Calcium uptake and release by skeletal-muscle mitochondria

THE EGTA - ruthenium red quench technique was used to obtain initial-velocity plots of Ca²⁺ uptake by skeletal-muscle mitochondria. The K_m was 5 μM and the Hill coefficient 1.9 at both 0° and 10°C. Inorganic phosphate stimulated and Mg²⁺ inhibited initial rates of transport. In experiments on Ca²⁺ release, the Na⁺ Ca²⁺ exchange was demonstrated. Factors influencing Ca²⁺ release during anaerobiosis include phosphate concentration and extent of Ca²⁺ loading. The results are discussed in relation to the possible participation of mitochondria in the calcium-ion regulation of muscle.