Secretin receptors in the neuroglioma hybrid cell line NG108‐15

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Abstract
Secretin receptors in membranes from the neuroblastoma-glioma hybrid cell line NG108-15 were investigated by 125I-secretin binding and adenylate cyclase activation. On both parameters the corresponding relative potencies of parent peptides were, respectively: secretin > helodermin > peptide histidine isoleucinamide = vasoactive intestinal peptide. With secretin analogs and secretin fragments, the order of potency for binding was: secretin = [Val5]secretin > [Ala2]secretin = [Ala11]secretin > [Ala4,Val5]secretin > [Ala4]secretin > [D-Phe4]secretin > [D-Phe2]secretin = secretin (2-27) > secretin (3-27) > secretin (7-27). Also, on adenylate cyclase, [D-Phe4]secretin, [D-Phe2]secretin, secretin (2-27) and secretin (3-27) were partial agonists while secretin (7-27) was ineffective. The differentiating agent N6,2''-O-dibutyryladenosine 3'',5''-monophosphate (1 mM) increased the density of secretin receptors and secretin-stimulated adenylate cyclase activity after a lag period of 4 h. After incubation for 24 h, receptor number and enzyme activity were increased 4- and 3-fold, respectively. These effects were inhibited totally by 1 .mu.g/ml cycloheximide and halved by 5 .mu.g/ml actinomycin D. They were mimicked by 1 mM sodium butyrate but were not reproduced by either 8-bromoadenosine 3'',5-monophosphate or the phosphodiesterase inhibitor rac-4-(3-Butoxy-4-methoxybenzyl)-2-imidazolidinone.