CHARACTERIZATION OF CCKB RECEPTORS ON GH(3) PITUITARY-CELLS - RECEPTOR ACTIVATION IS LINKED TO CA2+ MOBILIZATION

Cholecystokinin receptors on GH(3) rat anterior pituitary cells have b een characterised using radioligand binding and Ca2+ mobilisation. [I- 125]Bolton Hunter CCK-8s (BHCCK) bound dose dependently to GH(3) cells (K-d 85 pM, B-max 23 fmol/mg protein). Competition curves with CCK-8s (IC50 2.4 nM), pentagastrin (IC50 45 nM), L-365,260 (IC50 25 nM) and devazepide (IC50 820 nM), were consistent with a population predominan tly of CCKB receptors. Binding of [I-125]BHCCK to lysed cells was inhi bited by 10 mu M GTP-gamma-S and 10 mu M GppNHp, suggesting the recept or was linked to a guanine nucleotide binding protein. Intracellular C a2+ mobilisation was a functional consequence of CCKB receptor activat ion in GH(3) cells using the fluorescent dye fura-2. CCK-8s (0.1 nM-1 mu M) and the selective CCKB receptor agonist, pentagastrin, (0.1 nM-1 00 mu M) dose dependently increased intracellular Ca2+ with a similar maximal increase of 2.85-fold and 2.77-fold respectively. Response to a submaximal dose of the CCKB receptor agonist pentagastrin (100 nM) w as dose dependently blocked by the CCKB receptor antagonist L-365,260. GH(3) cells may therefore provide a useful model to study CCKB recept or coupling in a pituitary cell line.