Effect of stretch on contractility and ionic contents of the sartorius muscle of Rana pipiens.

KAPOPORT, STANLEY I., AND JEANNETTE M. BIDINGER. Eject of stretch on contractility and ionic contents of the sartorius muscle of Rana pipiens. Am. J. Physiol. 226(Z) : 452-457’ 1974.-When sartorius muscles of frogs are soaked in Ringer at room temperature, they gain Na, lose K, and lose contractility with time. These changes are retarded by stretching the muscles to ZO-30Y0 of their rest length. Conditions which inhibit the Na pump, such as soaking muscles in ouabain, K-free, or cold Ringer, abolish the differences in ionic contents and contractility between stretched and unstretched muscles. However, ouabain and K-free Ringer accelerate and cold retards the changes that occur in unstretched muscles in Ringer at room temperature. The results suggest that stretch stimulates the Na pump, either directly or indirectly through its effect on general metabolism. Contractility lasts longer in those muscles whose K contents are increased either by stretch or by different conditions of soaking.