Abstract
Abstract Cholecystokinin (CCK) receptors are currently divided into at least two subtypes: a CCK-A subtype, responsive to the sulfated form of cholecystokinin octapeptide (CCK-8) and selectively antagonized by L-364,718, and a CCK-B subtype, which shares equal affinities for gastrin and CCK-8. In the present study the receptor subtype that mediates guinea pig ileal secretion by evaluating the potencies of CCK- and gastrin-related peptides to evoke increases in transmucosal short-circuit current was characterized. The antagonist potencies of L-365,260 (CCK-B selective) and L-364,718 (CCK-A selective) against CCK-8 were also determined. Both CCK-8 and cerulein, when added to the serosal side of the tissue, evoked increases in the short-circuit current, having EC 50 values of 0.8 and 0.2 nmol/L, respectively. Desulfated (SO 3 ) CCK-8, CCK-4, gastrin 17 -I, pentagastrin, gastrin 17 -II, and gastrin 13 -I were relatively weak agonists (EC 50 > 1000 nmol/L. Cholecystokinin octapeptide-induced short-current responses were competitively antagonized by L-364,718 (pA 2 , 10.3) and L-365,260 (pA 2 , 7.4). The high selectivity of the tissue for sulfated CCK-8 suggests that the secretory effect of CCK-8 on guinea pig ileal electrolyte transport is mediated by a CCK-A receptor. The potent effect of L-364,718 against CCK-8 is also consistent with an action at the A-subtype receptor.
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