VPAC receptors

VIP binds two receptors, VPAC1 and VPAC2, which it shares with its cousin PACAP. Both are G-protein receptors that raise cyclic AMP inside the cell. VPAC1 sits on gut, lung, liver and immune cells; VPAC2 on smooth muscle, the pancreas and the brain's clock. Cyclic AMP relaxes muscle, opens vessels and quiets immune cells.