A new type of functional VIP receptor has an affinity for helodermin in human SUP‐T1 lymphoblasts

Abstract
A new type of VIP receptor was characterized in human SUP‐T1 lymphoblasts. The order of potency of unlabeled peptides in the presence of [125I]helodermin, was: helodermin(1–35)‐NH2 = helodermin(1–27)‐NH2 > helospectin > VIP = PHI > [D‐Ser2]VIP > [D‐Asp3]VIP > [D‐His1]VIP ⩾ [D‐Ala4]VIP 2̆ secretin = GRF. This specificity was distinct from that of all VIP receptors described so far in that: (i) the affinity for helodermin (Kd = 3 nM) was higher than that of VIP (Kd = 15 nM) and PHI (Kd = 20 nM); and (ii) position 4 played an important role in ligand binding. The labeled sites were likely to be functional receptors as adenylate cyclase in crude lymphoblastic membranes (200‐10 000 × g pellets) was stimulated by peptides, in the presence of GTP, with the following order of potency: helodermin(1–35)‐NH2 > helo‐dermin(1–27)‐NH2 > helospectin = VIP = PHI.