CALCITONIN-GENE-RELATED PEPTIDE RECEPTORS IN HUMAN GASTROINTESTINAL EPITHELIA

1 The secretory responses to calcitonin gene-related peptide (CGRP) re ceptor agonists have been characterized in two human adenocarcinoma ce ll lines, namely HCA-7 and Colony-29 (Col-29) epithelia. These cells f orm polarized epithelial layers when grown on permeable supports and a llow changes in electrogenic ion transport in response to agonists to be monitored continuously. 2 alpha-CGRP (rat and human sequences), rat beta-CGRP and human [Tyr(0)]CGRP applied to the basolateral surface w ere found to be full agonists, causing prolonged increases in short-ci rcuit current. Concentration-response curves exhibited EC(50) values o f 0.6-1.5 nM in HCA-7 cells. The same agonists were less effective in Col-29 epithelia, the EC(50) values ranging from 1 to 10 nM in these c ells. [Cys(ACM)2,7]CGRP was effective in both cell lines and was more potent in HCA-7 cells. 3 CGRP receptors were preferentially located on the basolateral surface in both cell types. Addition of r alpha-CGRP to the apical domain produced significantly smaller secretory response s (8.1% in HCA-7 and 29.2% in Col-29) compared with those produced fol lowing basolateral application (100%). 4 In both cell lines r alpha-CG RP-elevated short-circuit current was inhibited by the loop diuretic p iretanide (200 mu M) and by somatostatin (100 nM). Pretreating epithel ia with the cyclo-oxygenase inhibitor, piroxicam (5 mu M) had no signi ficant effect upon CGRP responses in either cell line. 5 Rat alpha-CGR P (0.2 nM) responses in HCA-7 epithelia were inhibited by the C-termin al fragment CGRP(8-37) (1 mu M). Pretreatment of Col-29 cells with CGR P(8-37) did not, however, alter the size or profile of responses to r alpha-CGRP (1 nM). 6 We conclude that high-affinity CGRP receptors exi st on the basolateral surface of both cell lines, however they differ in their sensitivity to CGRP(8-37) and agonist orders of potency. Thus different CGRP receptor subtypes appear to predominate in these two e pithelial cell types.