Multiple signal pathways coupling VIP and PACAP receptors to calcium channels in hamster submandibular ganglion neurons

The Vasoactive intestinal polypeptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP) are two novel neuropeptides which produce particular biological effects caused by interaction with G-protein-coupled receptors. We have shown in a previous study where VIP and PACAP 38 inhibit voltage-dependent calcium channel (VDCC) currents (ICa) via G-proteins in hamster submandibular ganglion (SMG) neurons. In this study, we attempt to further characterize the signal transduction pathways of VIP-and PACAP 38-induced modulation of ICa. Application of 1 microM VIP and PACAP 38 inhibited ICa by 33.0 +/- 3.1% and 36.8 +/- 2.6%, respectively (mean +/- S.E.M., n = 8). Application of strong voltage prepulse attenuated PACAP 38-induced inhibition of ICa. Pretreatment of cAMP dependent protein kinase (PKA) activator attenuated VIP-induced inhibition, but not the PACAP 38-induced inhibition. Intracellular dialysis of the PKA inhibitor attenuated the VIP-induced inhibition, but not the PACAP 38-induced inhibition. Pretreatment of protein kinase C (PKC) activator and inhibitor attenuated VIP-induced inhibition, but not the PACAP 38-induced inhibition. Pretreatment of cholera toxin (CTX) attenuated PACAP 38-induced inhibition of ICa. These findings indicate that there are multiple signaling pathways in VIP and PACAP 38-induced inhibitions of ICa: one pathway would be the VPAC1/VPAC2 receptors-induced inhibition involving both the PKA and PKC, and another one concerns the PAC1 receptor-induced inhibition via Gs-protein betagamma subunits. The VIP-and PACAP 38-induced facilitation of ICa can be observed in the SMG neurons in addition to inhibiting of ICa.

Constitution of calcium channel current in hamster submandibular ganglion neurons

The submandibular ganglion (SMG) neuron has been well established as the parasympathetic ganglion that innervates the submandibular and sublingual salivary glands. Thus this neuron plays a key role in salivary secretion. In a previous study, we reported that SMG possessed T-, L-, N-, P/Q- and R-type voltage-dependent calcium channels (VDCCs). In this study, we analyzed the contribution of the distinct subtypes of VDCCs currents (ICa) using the whole-cell configuration of the patch clamp technique in SMG neurons. In addition, we also investigated the effects of a strong voltage prepulse on the contributions of the subtypes of VDCCs. In SMG neuronal ICa without a prepulse, the mean percentages of L-, N-, P-, Q- and R-type were 39.7, 31.5, 10.6, 7.1 and 7.9%. In SMG neuronal ICa with prepulse, the mean percentages of L-, N-, P-, Q- and R-type were 37.2, 34.0, 14.0, 7.6 and 7.0%. Thus, these results showed that SMG possess multiple types of VDCCs and that N- and P-type VDCCs are facilitated by a prepulse in SMG neurons.