The effect of Ca2+, temperature and sucrose upon potassium contracture of the isolated rat right ventricle.

Potassium (100 mM KC1) contracture of the isolated rat right ventricle was lower in Tyrode solution (37 mM Na) than on substituting sucrose (270 mM) for NaC1 and was biphasic in 70% of the experiments. As in slow (tonic) skeletal muscle, the maximum contracture value persisted as long as a raised KC1 concentration was maintained. Even after complete potassium depolarization it changed when Ca was altered. At 37 degrees C, the second phase of potassium contracture was higher than at 34 degrees C (p less than 0.01). The effect of K+ and Ca2+ was inhibited if the ions were added after adding sucrose to the Tyrode solution. Contracture of the rat ventricle resembled contracture of slow (tonic) skeletal muscle.