Changes in enzyme activities in smooth muscle after contractile activity in vitro

Abstract 1. 1. The effects of contractile activity in vitro on the activities of hcxokinase, glucose-6-phosphatc dehydrogenase, 6-phosphogluconate dehydrogenase, pyruvate kinase, lactate dehydrogenase, fumarasc, malate dehydrogenase, and cytochrome oxidase were investigated in the smooth muscle taenia coli from the guinea-pig. 2. 2. The muscles were stimulated to contractile activity for 3 hours by either high potassium medium or carbachol, followed by a hours recovery. 3. 3. The activities of hexokinase, glucose-6-phosphate dehydrogenase, and 6-phosphogluconate dehydrogenase were not affected by the stimulation. 4. 4. The contractile activity caused by the high-potassium medium increased the activities of pyruvate kinase, malatc dehydrogenase, and cytochrome oxidase, whereas carbachol stimulation also increased the activities of lactate dehydrogenase and fumarase. 5. 5. It is suggested that the increase in enzyme activities reflects an increased demand on energy metabolism caused by the induced contractile activity.