Pharmacological and biochemical evidence for the simultaneous expression of CCKB/gastrin and CCKA receptors in the pig pancreas

1 In the pig, the secretory response of the pancreas is not inhibited by the antagonist MK329 suggesting that cholecystokininA (CCKA) 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 [M125I]‐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 (Kd = 0.22 ± 0.02 nM) and a binding capacity, Bmax= 110.64±12.50 fmol mg−1 protein. 4 Competition binding by agonists and antagonists of CCKA and CCKB/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 CCKA and CCKB/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 CCKB/gastrin and CCKA receptors. 7 In pigs, as in calves and humans, CCKB/gastrin receptors are predominant in the pancreas.