Calcium oscillations in single cultured Chinese hamster ovary cells stably transfected with a cloned human cholecystokinin (CCK)(B) receptor

In Chinese hamster ovary cells stably expressing the cloned human cholecystokinin (CCK)(B)/gastrin receptor, cholecystokinin octapeptide (CCK-8) evoked increases in [Ca2+](i) monitored by digitized video imaging of fura-2 fluorescence ratios. At concentrations around 10 pM, CCK-8 elicited [Ca2+](i) oscillations, which were blocked by elimination of extracellular Ca2+, by a phospholipase C inhibitor, U-73122, by a protein kinase C inhibitor, H7, as well as by phospholipase A(2) (PLA(2)) inhibitors, ONO-RS-082 and aristolochic acid. At higher concentrations, CCK-8 induced a single biphasic [Ca2+](i) rise consisting of a large peak followed by a lower sustained plateau, while the response turned into [Ca2+](i) oscillation when the extracellular Ca2+ was eliminated or a PLA(2) inhibitor was included. CCK-8 stimulated the release of arachidonic acid, and this was inhibited by aristolochic acid. Arachidonic acid caused an increase in [Ca2+](i) which was dependent upon extracellular Ca2+. These results suggest that the activation of PLA(2) might be involved, at least in part, in the Ca2+ influx that maintains the sustained plateau phase of [Ca2+](i) as well as the [Ca2+](i) oscillation when CCKB receptors are stimulated.