Kinetics of calcium uptake in normal and dystrophic sarcoplasmic reticulum

Abstract

Fragmented sarcoplasmic reticulum from chicken muscle is known to accumulate calcium in the presence of adenosine triphosphate, and the uptake is augmented by oxalate. Comparison of the kinetics obtained from normal and dystrophic vesicles suggests tthat dystrophic SR can transport calcium at a faster initial rate. The model proposed by Van der Kloot is used to account for the kinetics of calcium accumulation. Uptake at room temperature and 0°C appears to follow a first-order transport mechanism with rate constants of 13.8/min/mg protein for normal vesicles and 28.5/min/mg protein for dystrophic vesicles at room temperature. At 0°C a rate constant of 0.5/min/mg protein is obtained for dystrophic vesicles. Diffusion of accumulated calcium ions back into the external solution occurs with a rate constant of 3.2 × 10 −3/min/mg protein in normal vesicles at room temperature and at 3.4 × 10 −3/min/mg protein at 0°C. The diffusion rate constant for dystrophic vesicles is 1.4 × 10 −3/min/mg protein at room temperature and approximately 6.4 × 10 −3/min/mg protein at 0°C. The increase in initial rate of calcium uptake by dystrophic vesicles is discussed with regard to the stage of the disease.