Generation of Cell Transfectants Expressing Cardiac Calcium Ion Channel and Calcium Indicator Protein Aequorin

Chinese hamster ovary (CHO) cells stably coexpressing cardiac calcium ion channel [L-type calcium channel or ryanodine receptor (RyR)] and the calcium- sensitive bioluminescent protein aequorin were generated by transfecting aequorin cDNA. In a selected clone, C1-17, carrying the L-type calcium channel, depolarization induced by high concentration of K+produces aequorin luminescence. In another clone, R3-7, carrying RyR, caffeine produces aequorin luminescence. In the presence of selective calcium ion channel blockers, the aequorin luminescence was inhibited in a dose-dependent manner. These results indicate that functionally expressed calcium ion channels in these transformants can be monitored through the activation of endogenous aequorin luminescence following a physiological signal similar to that of native calcium channel. Moreover, the aequorin system compared very well with Fura-2 measurements. Thus, the recombinant cell models, which expressed cloned calcium channel and aequorin, will contribute to the elucidation of Ca2+movement through the cell surface and intracellular calcium ion channels.