Calcium Oscillations in Single Cultured Chinese Hamster Ovary Cells Stably Transfected with a Cloned Human Cholecystokinin (CCK)B Receptor
Keiko Akagi, Taku Nagao and Tetsuro Urushidani (*)
Laboratory of Pharmacology and Toxicology, Graduate School of Pharmaceutical
Sciences, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113, Japan
(*) To whom correspondence should be addressed.
Abstract: 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 A2 (PLA2) 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 PLA2 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 PLA2 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.
Keywords: CCKB/gastrin receptor, [Ca2+]i oscillation, Fura-2, Protein
kinase C, Phospholipase A2