Calcitonin gene-related peptide receptor independently stimulates 3′,5′-cyclic adenosine monophosphate and Ca2+ signaling pathways

Calcitonin gene-related peptide (CGRP) is a neuropeptide with diverse biological properties including potent vasodilating activity. Recently, we reported the cloning of complementary DNAs (cDNAs) encoding the human and porcine CGRP receptors which share significant amino acid sequence homology with the human calcitonin receptor, a member of the recently described novel subfamily of G-protein-coupled 7TM receptors. Activation of this family of receptors has been shown to result in an increase in intracellular cAMP accumulation and calcium release. In this study, we demonstrate that HEK-293 cells expressing recombinant CGRP receptors (HEK-293HR or PR) respond to CGRP with increased intracellular calcium release (EC50 = 1.6 nM) in addition to the activation of adenylyl cyclase (EC50 = 1.4 nM). The effect of CGRP on adenylyl cyclase activation and calcium release was inhibited by CGRP (8-37), a CGRP receptor antagonist. Both effects were mediated by cholera toxin-sensitive G-proteins, but these two signal transduction pathways were independent of each other. While cholera toxin pretreatment of HEK-293PR cells resulted in permanent activation of adenylyl cyclase, the same pretreatment resulted in an inhibition of CGRP-mediated [Ca2+](i) release. Pertussis toxin was without effect on CGRP-mediated responses. In addition, CGRP-mediated calcium release appears to be due to release from a thapsigargin-sensitive intracellular calcium pool. These results show that the recombinant human as well as porcine CGRP receptor can independently increase both cAMP production and intracellular calcium release when stably expressed in the HEK-293 cell line.