[Ca²⁺]_i transients in CD9-expressing CHO cells. (A) Control CHO cells (trace 2), CD9-expressing CHO cells (trace 1), and CD9-expressing CHO cells that were given a CD9-specific sense (trace 3) or antisense oligonucleotide (trace 4) were exposed to IL-16 (bar) followed by ionomycin (arrows), and the intracellular levels of calcium were determined. Data from Fluo-4–loaded CHO cells typical of 2 to 10 cells from at least 3 separate cultures are shown. (B) CD9-expressing CHO cells were sequentially exposed to xestospongin C (Xe C) (first bar), IL-16 (second bar), and then ionomycin (arrow). The same population of CD9-expressing CHO cells was used in the experiments that led to the data presented in panels A and B. The experiments were carried out on the same day. Thus, the noninhibitor control for the xestospongin C data presented in panel B is trace 1 of panel A. (C) CD9-expressing CHO cells were sequentially exposed to wortmannin (first bar), IL-16 (second bar), and then to ionomycin (arrows, trace 2). The positive control cells for this experiment (trace 1) were CD9-expressing cells that did not encounter wortmannin before they were exposed to IL-16 and then ionomycin.