Mucosal gastrin receptor. IV. Binding specificity.

We used membrane preparations of rat oxyntic gland mucosa to test the binding of various gastrin analogues to the gastrin receptor. Using [125I]15-Leu G-17 as a marker, a concentration of 4 X 10(-9) M unlabeled G-17 inhibited binding 50%. The tetra-, penta-, and hexapeptides of gastrin caused similar 50% inhibitions of binding at concentrations of 1 X 10(-7) M, 3 X 10(-8) M, and 7 X 10(-9) M, respectively. The heptapeptide caused only slightly less inhibition than G-17, whereas the decapeptide was equivalent in potency. Neither the G-17 nor G-34 that had the active tetrapeptide removed caused 50% inhibition of binding. When compared to G-17, these analogues produced only a 25% inhibition of binding at concentrations of 10(-8) M. We also failed to inhibit binding more than 25% when we used an analogue that had the amide removed from the C-terminal phenylalanine. Atropine, metiamide, and mepyramine did not alter the binding of gastrin to receptor. The results of binding specificity approximate the changes in biological potency associated with these compounds. This study adds further support that the gastrin receptor in question is responsible for the physiological effects of the hormone.