Selectivity of cholecystokinin (CCK) receptor antagonists, MK-329 and L-365,260, for axonally-transported CCK binding sites on the rat vagus nerve.

The ability of the cholecystokinin (CCK) receptor antagonists, MK-329 and L-365,260, to selectively inhibit 125I-Bolton-Hunter-CCK8 binding to ligated rat vagus nerve in vitro was examined at concentrations ranging from 10(-10) M to 10(-6) M. Both antagonists inhibited binding to CCK binding sites accumulating proximal to ligatures on the cervical vagus. Incubation of nerve sections in the presence of both antagonists produced an additive effect, indicating that both CCK-A and CCK-B binding sites are transported towards the periphery. In contrast, CCK binding sites accumulating distal to the ligature possessed the pharmacological characteristics of the CCK-B receptor sub-type only.