Effects of drugs on depolarized plain muscle

Abstract

Smooth muscle preparation of diverse origins immersed in Ringer''s solutions in which Na is replaced by K retain their responsiveness to drugs. When immersed in K-Ringer''s solution (KCl or K2SO4), smooth muscle preparations contract and subsequently relax. Membrane potentials of smooth muscle cells from chick amnion were recorded with intracellular micro-electrodes, but none could be recorded after transferring the preparation to K2SO4- Ringer''s solution. After smooth muscle preparations have relaxed in K-containing solutions, they contract in response to acetylcholine and relax again when the drug is removed. Responses to electrical stimula- tion are greatly reduced in K-Ringer''s solution and the conducted response to a mechanical stimulus is abolished. These results suggest that stimulant and inhibitory drugs as well as drug antagonists may activate the contractile elements of muscle without the mediation of membrane depolarization.