Characterization and regulation of high affinity calcitonin gene-related peptide receptors in cultured neonatal rat cardiac myocytes.

Previous studies have shown that stimulation of cultured beating cardiac myocytes with calcitonin gene-related peptide (CGRP) produces increased beating frequency, increased cellular cAMP concentration, and a homologous desensitization of the cAMP-elevating action of CGRP. In the present study, the characteristics and regulation of [125I]CGRP binding sites in cultured cardiac myocytes were investigated. Binding of [125I] CGRP to membranes prepared from these cells was selective, saturable, and of high affinity. Scatchard transformation of the saturation isotherm generated a linear plot suggesting the existence of a homogeneous population of binding sites with an equilibrium binding constant of 41 ± 7 pM and maximum binding capacity of 31 ± 5 fmol/mg protein. Binding of [125I]CGRP to membranes was inhibited completely by guanosine 5′-(3-Othio) triphosphate (250 μM), suggesting association of the binding sites with a G protein. Consistent with the saturation binding data, association kinetic studies indicat...