Functional Calcitonin Gene-Related Peptide Subtype 2 Receptors in Porcine Coronary Arteries Are Identified as Calcitonin Gene-Related Peptide Subtype 1 Receptors by Radioligand Binding and Reverse Transcription-Polymerase Chain Reaction

• Published in: The Journal of pharmacology and experimental therapeutics 2001-12, Vol.299 (3), p.1086-1094
• Main Authors: Rorabaugh, B R, Scofield, M A, Smith, D D, Jeffries, W B, Abel, P W
• Format: Article
• Language: English
• Subjects: Animals; Calcitonin Gene-Related Peptide - metabolism; Calcitonin Receptor-Like Protein; Cells, Cultured; Coronary Vessels - physiology; Humans; Intracellular Signaling Peptides and Proteins; Iodine Radioisotopes; Kinetics; Membrane Proteins - genetics; Membrane Proteins - isolation & purification; Polymerase Chain Reaction; Radioligand Assay; Receptor Activity-Modifying Proteins; Receptors, Calcitonin - genetics; Receptors, Calcitonin - isolation & purification; Receptors, Calcitonin Gene-Related Peptide - physiology; RNA, Messenger - metabolism; Swine
• ISSN: 0022-3565; 1521-0103

Calcitonin gene-related peptide (CGRP) receptors are classified into CGRP subtype 1 (CGRP 1 ) and CGRP subtype 2 (CGRP 2 ) based on the affinity of the antagonist, human α (hα)-CGRP 8–37 . hα-CGRP 8–37 antagonizes CGRP 1 receptor-mediated responses with high affinity ( K B < 100 nM) and antagonizes CGRP 2 receptor-mediated responses with low affinity ( K B > 1 μM). CGRP 2 receptors have been previously reported to mediate relaxation of large porcine coronary arteries because this action is antagonized with low affinity by hα-CGRP 8–37 . In the present study, we used reverse transcription-polymerase chain reaction, radioligand binding, and values from our previously reported isolated tissue experiments to compare the CGRP receptor in porcine coronary arteries with the porcine CGRP 1 receptor stably expressed in human embryonic kidney (HEK) 293 cells. We identified calcitonin receptor-like receptor and receptor activity modifying protein 1 mRNA in coronary arteries. We also found that the ligand binding characteristics of the CGRP receptor in coronary arteries and the cloned CGRP 1 receptor were highly similar. K I values for hα-CGRP 8–37 were 6.6 and 5.7 nM in porcine coronary arteries and the cloned CGRP 1 receptor, respectively. The affinities ( K B ) of hα-CGRP 8–37 and five other antagonists were 22- to 707-fold lower in functional experiments measuring relaxation of coronary arteries than in radioligand binding experiments. Despite this difference in absolute affinity values, there was a high correlation of the rank order of affinity for the antagonists determined by the two methods. Thus hα-CGRP 8–37 antagonizes CGRP-induced relaxation of porcine coronary arteries with low affinity at the CGRP 1 receptor. Taken together, these data do not support the existence of the CGRP 2 receptor.