FIGURE 4.

Ca²⁺ is necessary but not sufficient by itself for agonist-evoked ATP release. A, cells were preincubated for 20 min with vehicle (Ctrl), 1 μm thapsigargin (Tg), or 10 μm BAPTA-AM (BAPTA), and ATP concentrations were measured off-line, 5 min following the addition of vehicle or 30 nm thrombin. Ebselen (30 μm) and βγ-metATP (300 μm) were added to cells 5–10 min prior addition of vehicle/thrombin. The data represent the mean ± S.E. of at least six separate experiments performed in quadruplicate. B, cells were incubated with vehicle, 30 nm thrombin, or 100 μm UTP, and ATP concentrations were measured as above. C, myo-[³H]inositol-labeled cells were incubated for 20 min with the indicated drugs, and the resulting [³H]inositol phosphates were separated and quantified as in Fig. 1D. Results are from four independent experiments performed with quadruplicate samples. D, cells were loaded with Fura-2-acetoxymethyl ester for 30 min and stimulated with 30 μm thrombin or 100 μm UTP. Fluorescence from 30–40 cells was acquired as described under “Experimental Procedures.” Representative tracings are illustrated; similar results were obtained in six independent experiments.