Kinetics of calcium transport by fragmented sarcoplasmic reticulum.

Calcium transport by sarcotubular vesicles (fragmented sarcoplasmic reticulum) from skeletal muscle of rats, rabbits, and humans follows Michaelis-Menten kinetics when studied in systems containing oxalate and low ratios of calcium to vesicle protein. Under these conditions different preparations of vesicles are characterized by their calcium concentrating ability, i.e. the constant level to which they lower the calcium concentration of the medium. K,,, and V,,, values for calcium transport by rat and human vesicles are now established, and the rates at which calcium leaks from vesicles at equilibrium are detied with the use of two different methods of studying exchange at equilibrium. Chlorpromazine, quinine, and quinidine are competitive inhibitors of calcium transport. Reduction of calcium to Michaelis-Menten kinetics should facilitate comparison of the calcium transport system in vesicles from various types of muscle.