Protein Synthesis and Enzyme Response to Contractile Activity in Skeletal Muscle

Abstract

IT was reported earlier¹ that increases in the specific creatine phosphokinase activity in the isolated frog sartorius muscle could be demonstrated in response to repeated isotonic contraction in vitro. A similar enzyme response has now been shown to take place when the frog sartorius muscle is made to contract isometrically once every 5 sec for 6 h at 18° C by stimuli of supramaximal intensity from a multi-electrode assembly of the type described by Hill². It is of interest that under conditions in which the creatine phosphokinase activity increased by 30 per cent to 40 per cent, no significant increase in tho ATPase of the whole homogenate could be demonstrated when it was measured in 2.5 mmolar ATP, 2.5 mmolar calcium chloride, 100 mmolar potassium chloride, arid 100 mmolar trans-hydrochloric acid, pH. 9.1. In these conditions of assay myosin is probably responsible for most of the ATPase activity, and so it can be concluded that the activity of this myofibrillar enzyme does not respond so readily to repeated contraction as do creatine phosphokinase and other sarcoplasmic enzymes. Preliminary experiments in which the frog sartorius was stimulated isometrically for up to 90 h at 2° C gave evidence of slight increases in the specific ATPase activity in the whole homogenate.