Separation of active and inactive (nonphosphorylating) Ca2+‐ATPase in sacroplasmic reticulum subfractions from low‐frequency‐stimulated rabbit muscle

Abstract
Chronic low‐frequency stimulation elicits in rabbit fast‐twitch muscle a partial inactivation of the sarcoplasmic reticulum (SR) Ca2+‐ATPase and Ca2+‐uptake activities. Inactive Ca2+‐ATPase was enriched in a light microsomal fraction by sucrose density gradient centrifugation after calcium oxalate loading in the presence of ATP. This fraction showed a reduced specific activity and phosphoprotein formation of the Ca2+‐transport ATPase. These results suggest that the inactivation of the Ca2+‐ATPase as induced by increased contractile activity, is confined to a specific SR vesicle population.

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