Fig. 4.

ATP levels in cell supernatant and effect of apyrase on necrotic RPTC supernatant-induced renal fibroblast death. The supernatant from necrotic RPTC (2 × 10⁵) were incubated in the presence or absence of apyrase (6 and/or 12 U/ml) in culture medium (1 ml) without cells for 6 h (A) or with NRK-49F for 20 h (B). The concentration of ATP was measured as described in materials and methods (A), or cell viability was assessed by the MTT assay (B). NRK-49F cells were treated with ATP for 20 h at the concentrations as indicated, and cell viability was assessed by the MTT assay (C), or 1 mM ATP and cells were harvested for immunoblot analysis of active PARP-1 and caspase-3 (D). Values are means ± SD of 3 independent experiments and expressed as the percentage of control. Bars with different letters (a–c) are significantly different from one another (P < 0.05).