Properties of receptors for gastrin and CCK on gastric smooth muscle cells.

Previous studies have demonstrated that cholecystokinin (CCK), gastrin, and structurally related peptides can interact with various types of receptors that can be distinguished by their relative affinities for agonists and antagonists. In the present study we examined the effect of gastrin, the COOH-terminal octapeptide of CCK (CCK-8), and the tetrapeptide of CCK (CG-4) on contraction of dispersed gastric smooth muscle cells from guinea pig and tested the ability of various CCK receptor antagonists to affect agonist-induced muscle cell contraction. For purposes of comparison we tested the effect of each antagonist on CCK-stimulated amylase secretion by pancreatic acini from guinea pig. On gastric smooth muscle cells, CCK-8, gastrin, and CG-4 were all full agonists. CCK-8 and gastrin were equipotent and CG-4 was 6,000-fold less potent. Each antagonist caused inhibition of CCK-stimulated contraction with relative potencies (IC50): L364,718 (4 microM) = CBZ-CCK-(27-32)-NH2 (3 microM) greater than proglumide analogue 10 (90 microM). Inhibition by each of the antagonists was competitive in nature, specific for CCK peptides, and each had the same IC50 whether contraction was stimulated by CCK-8, gastrin, or CG-4. Relative potencies (IC50) of the three antagonists for inhibiting CCK-stimulated amylase release from pancreatic acini were L364,718 (3 nM) greater than proglumide analogue 10 (200 nM) greater than CBZ-CCK-(27-32)-NH2 (3 microM). These results demonstrate that gastric smooth muscle cells possess receptors that differ from CCK receptors on pancreatic acini in terms of affinities for both agonists and certain antagonists.(ABSTRACT TRUNCATED AT 250 WORDS)