Neurokinin A depolarizes neurons of the guinea pig inferior mesenteric ganglia

Neurokinin A (NKA) applied either by superfusion (0.1-10 microM) or by pressure ejection evoked a slow membrane depolarization in neurons of the inferior mesenteric ganglia in vitro. The NKA-induced depolarization which was not significantly affected by reducing the Ca concentration or by tetrodotoxin was associated in most cases by a small-to-moderate increase in membrane resistance; however, conditioning hyperpolarization increased rather than decreased the response. The depolarization elicited by NKA was eliminated in the presence of substance P (SP) and the depolarization by SP in the presence of NKA. The results suggest that the actions of NKA on prevertebral neurons are similar to that of SP and that these two peptides may act on the same receptors or share similar ionic channels.