Effects of hypertonicity on frog muscle contractures induced by quinine.

1. Frog sartorius and extensor longus digiti ("toe") muscles were used to investigate the effects of solutions of two (2T) and three (3T) times normal tonicity on the contractures elicited by quinine or by high-[K]O media, and on twitch and tetanic tension. 2. Solution 2T had no effect on the peak amplitude of quinine-induced contractures (PQ) of toe muscle but increased the PQ of sartorius muscle. Toe muscle PQ was significantly reduced by 3T. The quinine-induced contractures of sartorii bathed in 3T were slower than, but reached peak values not significantly different from, those obtained with control Ringer solution (1T). 3. The twitch and tetanic contractions of both sartorius and toe muscles were partially or totally blocked by 2T and were always abolished by solution 3T. 4. The maximal amplitude of K+-induced contractures (PK) of toe muscle was significantly reduced, but not abolished, by solutions 2T and 3T. The PK of sartorius muscle was greater at 2T than at 1T, but, in contrast to the transient tension recorded for 1T, the K+-induced contracture in solution 2T had a prolonged plateau. 5. The results suggest that hypertonicity affects the contractile apparatus as well as the excitation-contraction coupling process. The enhancement of quinine- and K+-induced contractures is ascribed to inhibitory effects of hypertonicity on Ca2+-sequestration by the sarcoplasmic reticulum.