Pharmacological and biochemical evidence for the simultaneous expression of CCK(B)/gastrin and CCK(A) receptors in the pig pancreas

1. In the pig, the secretory response of the pancreas is not inhibited by the antagonist MK329 suggesting that cholecystokinin(A) (CCK(A)) receptors are not involved. 2. Membranes were isolated from the pancreas of 6 Large White pigs to characterize their CCK receptors. 3. The binding of [(125)I]-BH-[Thr, Nle]CCK-9 was dependent on pH, maximal after a 90 min incubation period, saturable and reversible. Saturation analysis of the binding demonstrated a single class of high affinity sites (K(d)=0.22±0.02 nM) and a binding capacity, B(max)=110.64±12.50 fmol mg(−1) protein. 4. Competition binding by agonists and antagonists of CCK(A) and CCK(B)/gastrin receptors demonstrated the presence of two distinct binding components, sites presenting a high affinity for [Thr, Nle]CCK-9, gastrin, PD 135158, L-365,260 and a low affinity for MK329, SR 27897, and sites presenting a high affinity for [Thr, Nle]CCK-9, MK329, SR 27897 and a low affinity for gastrin, PD 135158, L-365,260. 5. These pharmacological data demonstrate the presence of both CCK(A) and CCK(B)/gastrin receptors in the pig pancreas, the latter being predominant. 6. Two distinct membrane proteins (50 and 85–100 kDa, respectively) display pharmacological features of CCK(B)/gastrin and CCK(A) receptors. 7. In pigs, as in calves and humans, CCK(B)/gastrin receptors are predominant in the pancreas