Abstract
Caleitonin-gene related peptide (CGRP) receptors en porcine aorta endothelium(PAE) membranes and on porcine coronary artery smooth muscle (PCASM) membranes were labeled with 125I-[His10] -h-αCGRP. h aCGRP bound to a single class of binding sites in these t issues with Ki values of 0.88 nM and 0.36 nM, respectively. The antagonist h-αCGRP(8 - 37) bound to high- and low-affinity sites in both tissues with Ki values of 2.9 nM and 83 nM in 2AE and 1.7 nM and 68 nM in PCASM. In isolated ring segments of porcine left circumflex coronary arteries studied in vitro; h-αCGRP completely relaxed KCl-induced tone with an ECSC of 3.6 nM. The petency of h-αCGRP was r.ot altered by removal of the endothelium, :ncubat:on with indomethacin (10-5 M) or NG-nitro-L-arginine (10-4 M). The affinity of h-αCGRp (8-37) in blocking h-o-CGRP relaxation, calculated from Schild regressions, was 1.3 μM. These results show that haCGRP-induced relaxation of pig coronary arteries is independent of the endothelium and suggest r hat the low affinity CGRP receptor is linked to relaxation. The function of the endothelial CGRP receptors is unknown.