PROPERTIES OF THE PITUITARY ADENYLATE CYCLASE-ACTIVATING POLYPEPTIDE-I AND POLYPEPTIDE-II RECEPTORS, VASOACTIVE INTESTINAL PEPTIDE(1), AND CHIMERIC AMINO-TERMINAL PITUITARY ADENYLATE CYCLASE-ACTIVATING POLYPEPTIDE VASOACTIVE INTESTINAL PEPTIDE(1) RECEPTORS - EVIDENCE FOR MULTIPLE RECEPTOR STATES

We analyzed the functional and binding properties of the ''normal'' pi tuitary adenylate cyclase-activating polypeptide (N-PACAP) type l, PAC AP type II/vasoactive intestinal peptide (VIP)(1), and chimeric N-PACA P/VIP1 receptors expressed in Chinese hamster ovary cells. The binding properties of the three receptors were investigated using three radio iodinated tracers: I-125-VIP, I-125-PACAP-27, and I-125-PACAP-29 (I-12 5-PACAP-27-Gly28,Lys29-amide). The three tracers labeled very differen t receptor densities; I-125-PACAP-29 labeled more receptors than eithe r I-125-VIP Or I-125-PACAP-27 in the three cell lines. Analysis of the competition curves suggested that the three tracers labeled in a diff erent manner three PACAP I receptor states, two PACAP II/VIP1 receptor states, and three chimeric N-PACAP/VIP1 receptor states in transfecte d Chinese hamster ovary cells. The previously described PACAP(1A) and PACAP(1B) receptors, which differ by their affinities for PACAP-27 and PACAP-38, actually correspond to different PACAP I receptor states. T he three receptors were able to increase adenylate cyclase activity wh en activated by PACAP-38, PACAP-27, or VIP. In contrast with the two p arent receptors, the chimeric N-PACAP/VIP1 receptor was activated by P ACAP-38 at lower concentrations than PACAP-27, suggesting that the ami no-terminal and core receptor domains influence each other and that th e conformation of one or both domains was altered in the chimeric comp ared with wild-type receptors. Comparison of the binding and functiona l properties of three clones expressing different chimeric N-PACAP/VIP 1, receptors densities indicated that I-125-PACAP-29 was necessary to correctly estimate the receptor number and that I-125-PACAP-27 or I-12 5-VIP labeled only a fraction of the functional receptors. We suspect (but could not demonstrate) that this might also be true for PACAP I a nd PACAP II-VIP1 receptors.