NONMUSCARINIC STIMULATION AND BLOCK OF A SYMPATHETIC GANGLION BY 4-(m-CHLOROPHENYLCARBAMOYLOXY)-2-BUTYNYLTRIMETHYLAMMONIUM CHLORIDE (McN-A-343)

¹ Department of Pharmacology, Tulane University School of Medicine, New Orleans, Louisiana

Ganglionic firing produced by 4-(m-chlorophenylcarbamoyloxy)-2-butynyltrimethylammonium chloride (McN-A-343) in the cat superior cervical ganghion had two components: a late-occurring response that was prevented by atropine and an early-occurring response that was resistant to blockade by either hexamethonium (C₆) or atropine. The discharge was accompanied by a sustained depolarization. Whereas small doses of McN-A-343 enhanced transmission, large doses caused ganglionic blockade. Atropine had no effect on the blocking actions of McN-A-343. Although the blockade by McN-A-343 was antagonized by tetanic pregangiionic stimulation, the block was not frequency-dependent. Ganglionic firing by KCl, acetylcholine or tetramethylammonium was enhanced at a time when transmission was blocked. Furtrethonium and its 5-methyl derivative have ganglionic actions identical to those of McN-A-343. It was concluded that these compounds stimulate two distinctive types of ganglionic receptors and cause a blockade of transmission by a mechanism different from that of C₆.