The uptake of Ca 2+ and Sr 2+ by fractions from lobster muscle

Abstract

1. 1. Vesicles isolated by the differential centrifugation of homogenates of lobster muscle can accumulate Ca 2+, lowering the Ca 2+ concentrations in the external solution to below 10 −7 M. 2. 2. The uptake of Ca 2+ by the vesicles requires an energy source, like ATP, and is potentiated by oxylate—just like the preparations from mammalian muscle. 3. 3. Vesicles isolated from lobster muscle can accumulate Sr 2+. 4. 4. A model is proposed to account for the kinetics of divalent cation accumulation. Uptake at 0°C is by a first-order transport mechanism with a rate constant of about 0·6/min mg protein at 0°C. The divalent cation accumulated in the vesicles diffuses back to the external solution with a rate constant of about 1·2×10 3/min mg protein. 5. 5. The results are discussed with regard to the role of divalent cations in the production of action potentials in crustacean muscle fibers and the part played by the sarcoplasmic reticulum in excitation-contraction coupling.