Distinct receptors for cholecystokinin and gastrin on muscle cells of stomach and gallbladder.

A technique of receptor protection that enables selective preservation of one receptor type was used in conjunction with preferential antagonists of cholecystokinin (L364,718) and gastrin (L365,260) to characterize cholecystokinin (CCK) and gastrin receptors on isolated single muscle cells of the guinea pig stomach and gallbladder. In gastric muscle cells, CCK-8 and gastrin-17 were equipotent and the concentration causing 50% inhibition of response (IC50) values of both antagonists were independent of the agonist, whereas in gallbladder muscle cells, CCK-8 was more potent than gastrin-17 and the IC50 values of the antagonists were dependent on the agonist. In gastric muscle cells, CCK-8, gastrin-17, and L364,718 protected completely the response to CCK-8 or gastrin-17, and L365,260 protected partially but equally the response to both agonists. In gallbladder muscle cells, CCK-8 and L364,718 protected completely and gastrin-17 and L365,260 protected partially the response to CCK-8; conversely, gastrin-17 and L365,260 protected completely and CCK-8 and L364,718 protected partially the response to gastrin-17. The patterns of response in muscle cells from the two regions indicate the presence of one receptor type in gastric muscle cells that interacts equally with gastrin and CCK, and of two receptor types in gallbladder muscle cells, one of which interacts preferentially with CCK and the other preferentially with gastrin.