Tetracaine blocks the responses of isolated acinar cells from rat parotid to carbachol but not to substance P

Carbachol and substance P stimulated ⁴⁵Ca²⁺ flux changes, ⁸⁶Rb⁺ efflux, and amylase secretion from acinar cells isolated fromrat parotid. The local anesthetic tetracaine blocked all of these measured responsed to carbachol, but none of the responses to substance P. Tetracaine must act at either the cholinergic receptor or at a subsequent transducing step in the cholinergic stimulus-response sequence. If tetracaine acts at one of the transducing steps between cholinergic receptor occupation and the physiological responses then the action of tetracaine must be at a locus in the cholinergic reaction scheme not shared by substance P, because tetracaine did not block any response of the parotid to substance P.