MEMBRANE POTENTIAL CHANGES ASSOCIATED WITH TACHYPHYLAXIS AND POTENTIATION OF THE RESPONSE TO STIMULATING DRUGS IN SMOOTH MUSCLE

Abstract

Conditions which affect the response of smooth muscle to repeated application of stimulating drugs have been investigated. In guinea‐pig taenia coli, tension changes were recorded simultaneously with membrane potential changes using the sucrose gap technique. Acetylcholine, histamine, and 5‐hydroxytryptamine caused depolarization and, after removal of the drug, hyperpolarization which was followed by a sequence of damped oscillations of the membrane potential. The average rate of depolarization decreased in the order acetylcholine > histamine > 5‐hydroxytryptamine. The readiness with which tachyphylaxis occurred increased in the order acetylcholine