A digital imaging fluorescence microscope was used to study the effect of a protein kinase inhibitor staurosporine on the antigen-dependent calcium signals in an individual rat basophilic leukemia cell (RBL-2H3). Although dose dependency of staurosporine was different from one cell to another, staurosporine inhibited, at low concentration, the calcium influx from the external medium into RBL-2H3 cells. At high concentration, however, it inhibited both the removal of calcium ion from internal stores and the calcium influx from the external medium. These results indicated that staurosporine is necessary for the inhibition of the calcium influx from the external medium and that a protein kinase (possibly protein kinase C) is involved in the calcium influx from the external medium into the cytoplasm.
