CHARACTERIZATION OF THE MUSCARINE RECEPTOR SUBTYPE ON SYMPATHETIC-NERVE ENDINGS IN THE RAT CAUDAL ARTERY

The prejunctional muscarine receptor on sympathetic nerves in the rat caudal artery was characterized using several selective antagonists. T he inhibitory response of carbachol on vasoconstriction elicited by sy mpathetic nerve stimulation was antagonized by benzhexol (trihexypheni dyl; pK(B) 7.1), heptane-1,7-bis(dimethyl-3'-phthalimidopropyl ammoniu m bromide) (C-7/3-phth; pK(B) 6.5) and hexahydrosiladifenidol (HHSiD; apparent pK(B) 6.0). These pK(B) values suggest that the receptor most closely resembles the muscarine M(2) receptor subtype rather than the muscarine M(1), M(3) or M(4) receptor subtypes.