Pharmacological and biochemical characterization of cholecystokinin/gastrin receptors in developing rat pancreas

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Abstract
Cholecystokinin/gastrin receptors in the pancreas of newborn (3‐day‐old) rats are of type A, as in control mature rats, revealed by pharmacological analysis of specific 125I‐Bolton‐Hunter‐reagent‐labelled [Thr34,Ahx37]cholecystokinin(31–39) (Ahx, aminohexanoic acid) binding. Also, by 1 day post‐partum, pancreatic cholecystokinin receptors were shown to be coupled to guanine‐nucleo‐tide‐binding regulatory (G) proteins. Scatchard analysis of 125I‐Bolton‐Hunter‐reagent‐labelled [Thr34,Ahx37]cholecystokinin(31–39) binding to pancreatic membranes from rats at different times after birth showed a slight increase in the binding capacity of cholecystokinin receptors between days 3 and 14 and a sixfold increase in 21‐day‐old rats, with no change in receptor affinity during development. SDS/PAGE analysis of pancreatic membranes affinity labelled with the photoactivable ligand 125I‐[2‐(p‐azidosalicylamido)‐1,3′‐dithiopropionate]‐labelled [Thr34,Ahx37]cholecystokinin‐(31–39) identified cholecystokinin receptors of 100–135 kDa in 3‐day‐old rats, 96–130 kDa in 7‐day‐old rats, 90–125 kDa in 10‐day‐old rats and 85–100 kDa in 14‐day‐old and 21‐day‐old rats, as found in control adult rats. Endo‐β‐N‐acetylglucosaminidase F treatment yielded a core protein of 42 kDa in all developmental stages. These findings are consistent with an age‐related postnatal expression of distinct glycoforms of pancreatic cholecystokinin receptors. Furthermore, it was observed that the period 2–3 weeks after birth, characterized by stabilization of the mass of the cholecystokinin receptor, precedes the dramatic increase in the receptor number.

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