VIP and PACAP potentiation of nicotinic ACh-evoked currents in rat parasympathetic neurons is mediated by G-protein activation

The effects of vasoactive intestinal polypeptide (VIP) and pituitary adenyl ate cyclase-activating polypeptide (PACAP27 and PACAP38) on isolated parasy mpathetic neurons of rat intracardiac and submandibular ganglia were examin ed under voltage clamp using whole-cell patch-clamp recording techniques. V IP and PACAP (less than or equal to 10 nm) selectively and reversibly incre ased the affinity of nicotinic acetylcholine receptor channels (nAChRs) for their agonists resulting in a potentiation of acetylcholine (ACh)-evoked w hole-cell currents at low agonist concentrations. VIP-induced potentiation was observed with either ACh or nicotine as the cholinergic agonist. The VI P- but not the PACAP-induced potentiation of ACh-evoked currents was inhibi ted by [Ac-Tyr(1), D-Phe(2)]-GRF 1-29, amide (100 nm), a selective antagoni st of VPAC(1) and VPAC(2) receptors; whereas the PACAP38- but not the VIP-i nduced potentiation was inhibited by 100 nm PACAP6-38, a PAC(1) and VPAC(2) receptor antagonist. The signal transduction pathway mediating VIP- and PA CAP-induced potentiation of nicotinic ACh-evoked currents involves a pertus sis toxin (PTX)-sensitive G-protein. Intracellular application of 200 mu m GTP gamma S or GDP beta S inhibited VIP-induced potentiation of ACh-evoked whole-cell currents. GTP gamma S alone potentiated ACh- and nicotine-evoked currents and the magnitude of these currents was not further increased by VIP or PACAP. The G-protein subtype modulating the neuronal nAChRs was exam ined by intracellular dialysis with antibodies directed against alpha(o), a lpha(i-1,2), alpha(i-3) or beta G-protein subunits. Only the anti-G alpha(o ) and anti-G beta antibodies significantly inhibited the effect of VIP and PACAP on ACh-evoked currents. The potentiation of ACh-evoked currents by VI P and PACAP may be mediated by a membrane-delimited signal transduction cas cade involving the PTX-sensitive G(o) protein.