Figure 1.

VIP/PACAP ligand/receptor interactions. (A) IUPHAR and gene names are indicated in standard text and italics respectively. PAC₁ receptors are highly selective for PACAP and are generally only responsive to PACAP. VPAC₁ and VPAC₂, on the other hand, serve as physiological receptors for either PACAP or VIP, depending on the specific neuropeptide released from nearby cells or axon terminals. (B) General interaction of PACAP and VIP with their cell surface receptors. Each of the receptors is a seven-transmembrane GPCR coupled primarily via Gs to adenylate cyclase. Other pathways can be activated via βγ subunits, and by alternative coupling of the receptors to other G-proteins such as Gi and Gq (see text).