Specific labelling by [125I]helodermin of high‐affinity VIP receptors in rat liver membranes

Abstract
Helodermin, a newly isolated peptide from Gila Monster venom, is structurally related to VIP and secretin. When used as radioligand, [125I]helodermin bound rapidly and reversibly to crude rat liver membranes, the dissociation being accelerated by GTP. Competition binding curves of [125I]helodermin and [125I]VIP with unlabelled peptides showed the following order of decreasing affinity: VIP > helodermin > secretin > hpGRF(1–29)‐NH2. The shape of binding curves and of concurrent adenylate cyclase activation is compatible with the specific labelling, by [125I]helodermin, of a class of high‐affinity VIP receptors that is capable to stimulate adenylate cyclase.

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