Preparation of sarcoplasmic reticulum with high calcium-sensitive ATPase and stable calcium transport function from rat skeletal muscle.

A method was developed for the isolation from rat skeletal muscle of sarcoplasmic reticulum vesicles in which the calcium transport function does not decay during storage. High initial and maximum uptake of calcium and calcium-dependent ATPase activity were obtained for membranes isolated from mixed muscles or pure red fibers. Unstable vesicles resulted when 2 mM EDTA was included in the isolation medium. The calcium uptake activity was lost upon ageing at 0 degrees C, probably due to conversion of the calcium-dependent ATPase to a calcium-independent form. Addition of Ca2+ counteracted the affects of EDTA, suggesting their involvement in maintaining the structure of the calcium transport system. This is supported by the fact that different structural states of the ATPase in stable and unstable vesicles were detected by DEAE-cellulose column chromatography.