Action of surugatoxin on nicotinic receptors in the superior cervical ganglion of the rat.

Surugatoxin (SGTX, 0.1-2 muM) reversibly depressed orthodromic transmission and antagonized the depolarizing action of carbachol on the isolated superior cervical ganglion of the rat. The apparent dissociation equilibrium constant against carbachol-induced depolarization (measured in the presence of hyoscine) was 58 and 76 nM determined at 0.2 and 2 muM respectively. SGTX (2muM) did not reduce the depolarizing effects of (+/-)-muscarine, gamma-aminobutyric acid or angiotensin, but did reduce that to 5-hydroxytryptamine. Release of [3H]-acetylcholine following repetitive (10 Hz) preganglionic sympathetic stimulation was maintained in the presence of 2 muM SGTX. It is concluded that SGTX has a high and selective affinity for ganglionic nicotinic receptors.