Cholecystokinin receptors on GH3 rat anterior pituitary cells have been characterised using radioligand binding and Ca2+ mobilisation. [125I]Bolton Hunter CCK-8s (BHCCK) bound dose dependently to GH3 cells (Kd 85 pM, Bmax 23 fmol/mg protein). Competition curves with CCK-8s (IC50 2.4 nM), pentagastrin (IC50 25 nM) and devazepide (IC50 820 nM), were consistent with a population predominantly of CCKB receptors. Binding of [125I]BHCCK to lysed cells was inhibited by 10 microM GTP-gamma-S and 10 microM GppNHp, suggesting the receptor was linked to a guanine nucleotide binding protein. Intracellular Ca2+ mobilisation was a functional consequence of CCKB receptor activation in GH3 cells using the fluorescent dye fura-2. CCK-8s (0.1 nM-1 microM) and the selective CCKB receptor agonist, pentagastrin, (0.1 nM-100 microM) 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) was dose dependently blocked by the CCKB receptor antagonist L-365,260. GH3 cells may therefore provide a useful model to study CCKB receptor coupling in a pituitary cell line.