Effects of nitro-L-arginine (L-NA) and iberiotoxin on smooth muscle hyperpolarization induced by substance P, NOR-1 and bradykinin in segments of intact porcine coronary arteries. 10 μM indomethacin (indo) was present throughout. (a) Typical trace showing hyperpolarizations induced by bolus application of substance P (SP), NOR-1 and bradykinin (BK) in the absence and presence of iberiotoxin (IbTX). (b) Graphical representation of data from four separate experiments of the types shown in (a) in which each column represents the membrane potential (m.p.),+or−s.e.mean, before and after exposure to bolus doses of substance P (SP; 1 nmol), NOR-1 (100 nmol) or bradykinin (BK; 300 pmol) calculated to give, transiently, the final bath concentrations indicated. Responses are shown before (control) or after exposure to 100 μM nitro-L-arginine and, in its continued presence, to 100 nM iberiotoxin.