Characterization of calcitonin gene-related peptide receptors and adenylate cyclase response in the murine macrophage cell line P388 D1.

Specific receptors for calcitonin gene-related peptide (CGRP) were identified and characterized on plasma membranes from the interleukin-1 secreting murine macrophage-like cells line P388 D1. The binding of [125I]-rat CGRP I was time-dependent, reversible and the rate of dissociation of [125I]-rat CGRP I increased in the presence of GTP. Scatchard analysis was consistent with a single class of binding sites, with an apparent dissociation constant of 1.76 nM and a maximal binding capacity of 85.48 fmol/mg protein. In competitive displacement studies, rat CGRP I, human CGRP I and human CGRP II were equipotent to inhibit the binding of [125I]-rat CGRP I (IC50 = 4 nM) while rat CGRP II and the synthetic analogue [tyr(o)]-human CGRP I were ten-fold less potent. Porcine calcitonin and VIP did not inhibit tracer binding. In the presence of GTP, CGRP stimulation of adenylate cyclase was dose-dependent and strongly correlated with receptor occupation. These results indicate that the P388 D1 macrophage-like cell line expresses CGRP specific receptors functionally coupled to adenylate cyclase, which may be involved in CGRP-mediated macrophage immune response.