The possible involvement of Na+ ions in corticosterone-induced hypercontractility in the rat anococcygeus muscle.

The possibility that corticosterone-induced hypercontractility in the rat anococcygeus muscle might be due to an intramuscular redistribution of Na+ was investigated. 2 The contractility of the isolated muscle to noradrenaline (NA) was directly dependent on the Na+ concentration of the Krebs solution. 3 There was a linear relationship between the maximum contractile response of the muscle to NA and the Na+ concentration of the Krebs solution. 4 Muscle contractility was also increased by the presence of ouabain (10(-4)M) in the bathing medium. 5 Muscles from rats treated with corticosterone exhibited increases in both total and ouabain-sensitive ATPase activity. 6 The relationship between corticosterone, Na+ distribution, and muscle contractility is discussed.