Enzyme activities in skeletal muscle after contractile activity in vitro

Abstract 1. 1. Changes in muscle enzyme activities following isometric and isotonic contractile activity of electrically stimulated plantaris longus from frog were studied in vitro . The effect of contractile activity under hypoxic conditions and the time-course of changes in enzyme activities after exercise were also investigated. 2. 2. Isometric contractile work caused decreased activities in creatine phosphokinase, phosphorylase and phosphofructokinase and increased activities in hexokinase and cytochrome oxidase. The activity levels of glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, pyruvate kinase, lactate dehydrogenase and fumarase were not significantly different from control values. 3. 3. After isotonic contraction no significant changes in creatine phosphokinase, phosphorylase and phosphofructokinase activities were seen. Besides hexokinase and cytochrome oxidase, fumarase, glucose-6-phosphate dehydrogenase and 6-phosphogluconate deh ydrogenase activities were also increased. 4. 4. There were no significant differences between the enzyme response obtained after isometric contractions in deoxygenated or oxygenated medium. 5. 5. After a recovery period for 5 hours following isometric work the activities of hexokinase, the hexose monophosphate shunt dehydrogenases, fumarase and cytochrome oxidase showed increased activities. These declined to control values after 20 hours recovery except for hexokinase and 6-phosphogluconate dehydrogenase. The activity levels of creatine phosphokinase, phosphorylase and phosphofructokinase were progressively decreased during the recovery period. Pyruvate kinase and lactate dehydrogenase also showed decreased activity values after 20 hours recovery.