CGRP(2) receptor in the internal anal sphincter of the rat: implications for CGRP receptor classification.
The CGRP receptor mediating relaxation of the rat internal anal sphincter (IAS) has been characterized using CGRP analogues, homologues, the antagonist CGRP(8 - 37) and its analogues. In isolated IAS strips, the spontaneously developed tone was concentration-dependently relaxed by halpha CGRP, hbeta CGRP and rat beta CGRP (pEC(50) 8.1+/-0.2, 8.3+/-0.1 and 8.4+/-0.2, respectively; 100% maximum response). Vasoactive intestinal polypeptide (VIP) was around 7 fold more potent than halpha CGRP (pEC(50) 9.0+/-0.1; 100% maximum relaxation). [Cys(ACM(2.7))] halpha CGRP and salmon calcitonin were inactive (up to 10(-5) M). Halpha CGRP(8 - 37) (10(-5) M) antagonized responses to halpha CGRP (apparent pK(B) 5.7+/-0.3) and rat beta CGRP (apparent pK(B) 5.8+/-0.2), but not to VIP. Hbeta CGRP(8 - 37) (10(-5) M) was an antagonist against halpha CGRP (apparent pK(B) 6.1+/-0.1). Halpha CGRP(8 - 37) analogues (10(-5) M), with substitutions at the N-terminus by either glycine(8) or des-NH(2) valine(8) or proline(8), antagonized halpha CGRP responses with similar affinities (apparent pK(B) 5.8+/-0.1, 5.8+/-0.1 and 5.5+/-0.1, respectively). Peptidase inhibitors (amastatin, bestatin, captopril, phosphoramidon and thiorphan, 10(-6) M each) did not increase the agonist potency of either halpha CGRP or [Cys(ACM(2,7))] halpha CGRP, or the antagonist affinity of halpha CGRP(8 - 37) against halpha CGRP or rat beta CGRP. These data demonstrate for the first time a CGRP receptor in the rat IAS for which halpha CGRP (8 - 37) and its analogues have an affinity that is consistent with a CGRP(2) receptor. However, there is a marked species difference as the antagonist has a 100 fold lower affinity in the rat than in the same tissue of the opossum (Chakder & Rattan, 1991).
Wisskirchen
F M
FM
Department of Pharmacology, University College London, Gower Street, London WC1E 6BT.
Marshall
I
I
D001003:Anal Canal / Q000378:metabolism*; D000818:Animals; D015740:Calcitonin Gene-Related Peptide / Q000737:chemistry / Q000494:pharmacology*; D000077221:Calcitonin Gene-Related Peptide Receptor Antagonists; D004347:Drug Interactions; D006801:Humans; D008297:Male; D009893:Opossums; D010446:Peptide Fragments / Q000737:chemistry / Q000494:pharmacology; D010447:Peptide Hydrolases / Q000378:metabolism; D011480:Protease Inhibitors / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D018015:Receptors, Calcitonin Gene-Related Peptide / Q000819:agonists / Q000145:classification* / Q000378:metabolism; D013779:Tetrodotoxin / Q000494:pharmacology; D014649:Vas Deferens / Q000378:metabolism; D014660:Vasoactive Intestinal Peptide / Q000494:pharmacology
D000077221:Calcitonin Gene-Related Peptide Receptor Antagonists; D010446:Peptide Fragments; D011480:Protease Inhibitors; D018015:Receptors, Calcitonin Gene-Related Peptide; C058636:calcitonin gene-related peptide (8-37); D014660:Vasoactive Intestinal Peptide; D013779:Tetrodotoxin; D010447:Peptide Hydrolases; D015740:Calcitonin Gene-Related Peptide