Abstract
1. The nature of KCl-induced relaxations of the rat anococcygeus muscle was investigated. 2. The relaxations were mimicked by other K+ salts, but not by NaCl. 3. The muscle was more susceptible to the relaxant effects of KCl than the contractile effects. 4. Addition of ouabain (100 micron) had no effect on the relaxations. 5. The relaxations were abolished by tetrodotoxin (5 microgram/ml), procaine (500 micron), and by section of the inhibitory nerves. 6. The results suggest that KCl-induced relaxations are due to stimulation of the inhibitory nerves by K+.