Inhibitory effect of methylmercuric chloride on the contraction mediated by muscarinic receptor of intestinal smooth muscle of the guinea-pig.

Effects of methylmercuric chloride (MMC) on the contractile responses to nerve and drug stimulation in the guinea-pig taenia coli were examined. MMC (25-50 microM) severely reduced both responses to electrical and pharmacological (nicotine) stimulation of cholinergic nerves without affecting the responses to direct stimulation of muscles. MMC also suppressed markedly the response to acetylcholine (ACh), but did not change the maximum response to ACh. Dose-inhibition curve for MMC on the response to nerve stimulation was quite similar to that on the response to externally applied ACh. MMC only at a high concentration slightly reduced the response to histamine. MMC depolarized the membrane of the smooth muscle by about 8 mV with the sucrose-gap method. However, conditioning depolarization of the muscle strip by a 25 mM-K solution did not suppress the response to ACh. It was suggested that MMC-induced inhibition of the responses of the guinea-pig taenia coli to cholinergic nerve stimulation resulted from the inactivation of the muscarinic receptor of the smooth muscle.