Evidence against Substance P as a neurotransmitter at the neuroepithelial junction in rat colonic mucosa

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Abstract
Substance P (SP) caused a concentration-dependent increase in short-circuit current of rat isolated colonic mucosal preparations (ED50 10 Nm). The SP antagonist [d-Arg1, d-Pro2, d-Trp7,9, Leu11]SP (50 μm) did not increase short-circuit current. Tetrodotoxin (3·1 μm) reduced the effect of a maximum concentration of SP (300 Nm). This reduction was increased when tetrodotoxin was given with [d-Arg1, d-Pro2, d-Trp7,9, Leu11]SP. Increases in short-circuit current produced by electrical field stimulation were not reduced by [d-Arg1, d-Pro2, d-Trp7,9, Leu11]SP. It is concluded that SP is not a transmitter at the neuroepithelial junction in rat colonic mucosa.