CCK-B receptor-mediated stimulation of polyphosphoinositide turnover in GH3 pituitary cells in response to cholecystokinin and pentagastrin.
CCK-B receptor-mediated polyphosphoinositide (PPI) turnover in GH3 pituitary cells has been examined and comparisons are made with Ca2+ mobilisation and receptor binding data, previously described. Sulphated cholecystokinin octapeptide (CCK-8s) and the CCK-B-selective agonist pentagastrin dose-dependently stimulated PPI turnover in GH3 cells with similar maximal increases of 3.0 fold and 3.3 fold, respectively, in production of [3H]inositol phosphates over control. Responses, measured over 30min periods in the presence of 10mM LiCl, were generally maximal for both agonists at 100nM. Consistent with their [125]Bolton Hunter CCK-8s (BHCCK) binding affinities and with effects on Ca2+ mobilisation, CCK-8s was slightly more potent than pentagastrin in stimulating PPI turnover (EC50s 1.3nM and 3.9nM respectively). Both peptides showed higher potency in the PPI assay than in Ca2+ studies. 100nM pentagastrin-induced PPI turnover was dose-dependently inhibited by the CCK-B receptor-selective antagonist L-365,260 (IC50 470nM) whilst the CCK-A receptor antagonist, devazepide, only produced weak partial inhibition (18% at 10,000nM). Antagonists alone were observed to depress control activity in PPI turnover but not in Ca2+ mobilisation assays. The selectivity of L-365,260 compared to devazepide was similar in binding studies to that for both 100nM pentagastrin-induced functional responses. Schild analysis of antagonism of PPI turnover by L-365,260 yielded a line with slope close to unity (1.07) and a pKB of 8.27+/-0.05.
Smith
A J
AJ
Merck, Sharp and Dohme Research Laboratories, Neuroscience Research Centre, Essex, UK.
Freedman
S B
SB
D000818:Animals; D002118:Calcium / Q000378:metabolism; D002478:Cells, Cultured; D003164:Competitive Bidding; D004305:Dose-Response Relationship, Drug; D006168:Guinea Pigs; D010418:Pentagastrin / Q000494:pharmacology*; D018129:Phosphatidylinositol Phosphates / Q000378:metabolism*; D010902:Pituitary Gland / Q000187:drug effects* / Q000378:metabolism; D043887:Receptor, Cholecystokinin B; D011949:Receptors, Cholecystokinin / Q000187:drug effects*; D012844:Sincalide / Q000494:pharmacology*
D018129:Phosphatidylinositol Phosphates; D043887:Receptor, Cholecystokinin B; D011949:Receptors, Cholecystokinin; D010418:Pentagastrin; D012844:Sincalide; D002118:Calcium