ACTION OF SURUGATOXIN ON NICOTINIC RECEPTORS IN THE SUPERIOR CERVICAL GANGLION OF THE RAT

Abstract
Surugatoxin (SGTX, 0.1–2 μm) 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 μm respectively. SGTX (2 μm) did not reduce the depolarizing effects of (±)-muscarine, γ-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 μm SGTX. It is concluded that SGTX has a high and selective affinity for ganglionic nicotinic receptors.