Caspase inhibition failed to protect HCN cells from insulin withdrawal-induced cell death. (A) Z-VAD.fmk failed to prevent insulin withdrawal-induced HCN cell death. On the other hand, apoptotic cell death induced by etoposide (E, 20 μM) or staurosporine (STS, 0.5 μM) in I(+) was effectively blocked by Z-VAD.fmk. Insulin presence and withdrawal were denoted as I(+) and I(−), respectively. Cell death was measured by PI/Hoechst staining and quantitative data are presented as the mean ± SD (n = 3). Statistical significance was determined with an ANOVA test by comparing within each treatment group with and without Z-VAD.fmk in the same day ***p < 0.001. (B) Inhibition of caspase 3 activation by Z-VAD.fmk. E, etoposide; STS, staurosporine; C, control.