Chronic stimulation of a predominantly fast skeletal muscle enhanced the expression of type I (slow muscle) Ca-ATPase and suppressed the expression of the type II (fast muscle) Ca-ATPase. Monoclonal antibodies IID and IIHI 1 against type I (slow) and type II (fast) isoxymes respectively, were used to type the Ca-ATPases of the isolated SR (sarcoplasmic reticulum) by Western blots, and the Ca-ATPases of the muscle fibers by immuno~st~h~s~y.Of the fibers from control muscles 8096 stained for the type II isoxyme and 20% for the type I isoxyme. Following chronic stimulation all fibers stained for type I isoxyme and none stained for type II isoxyme. Ca-ATPase isoxyme distribution in isolated SR confirmed this effect of chronic stimulation. The calcium uptake activities of homogenates of stimulated muscles were 22% of the control muscles. The Ca-ATPase and calcium-uptake activities of the isolated SR from stimulated muscles were, respectively, 32 and 45% of the control muscles.
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