The effect of potassium on frog stomach muscle.

1 KCl relaxed strips of frog stomach muscle. Usually, the effect was biphasic, i.e. contraction followed by relaxation at a concentration of 137 mM. 2 The effect was mimicked by K2SO4. 3 Ouabain (5 and 10 micrograms/ml) blocked the relaxations and reversed them to contractions. The tension of strips was not affected. 4 Phenoxybenzamine (1 microgram/ml) and procaine (20 micrograms/ml) inhibited the relaxations, potentiated the contractile component and lowered the tone of the muscle. 5 The relaxation and the tone were inhibited by papaverine (5 micrograms/ml) but the contractile component was unaffected. 6 It is suggested that potassium-induced relaxations are mediated through the activation of the sodium pump.