PITUITARY ADENYLATE CYCLASE-ACTIVATING POLYPEPTIDE (PACAP) VASOACTIVE-INTESTINAL-PEPTIDE (VIP) RECEPTOR SUBTYPES IN RAT-TISSUES - INVESTIGATION OF RECEPTOR-BINDING, A NOVEL VIP RECEPTOR ANTAGONIST AND CHEMICAL CROSS-LINKING

Receptors for pituitary adenylate cyclase-activating polypeptide (PACAP) have been subdivided into type I receptors and II receptors. Using rat brain stem as a tissue containing type I receptors and rat lung as a tissue containing type II receptors, we investigated the binding of I-125-labelled PACAP, vasoactive intestinal peptide (VIP) and the related peptide, helodermin to these and, by chemical cross-linking, the relative molecular weight of the receptors. Type I receptors showed an M(r) of 58,000 and type II an M(r) of 54,000. After deglycosylation type I receptors showed an M(r) of 49,000 and type II receptors an M(r) of 41,000 demonstrating a high degree of glycosylation of both subtypes. This compares with the predicted (unglycosylated) M(r)'s of the recently cloned rat brain type I receptor and rat lung type II receptor of 56,000 and 49,000, respectively. We also studied a hybrid VIP receptor antagonist (VIP-neurotensin) and showed it was unable to displace I-125-PACAP from type I receptors (K-i>10 mu M) but was effective at type II receptors and propose that this peptide could be used to differentiate between PACAP effects at the two receptor subtypes.