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Figure 1 (A) Histochemical determination of cell viability and apoptotic myocytes. Cardiac myocytes were treated with serum-free DMEM alone (a and e), 10^–6 mol/l of doxorubicin (b and f), 10^–6 mol/l of doxorubicin in the presence of 10^–6 mol/l of amlodipine (c and g), or 10^–6 mol/l of doxorubicin in the presence of 10^–6 mol/l of nifedipine (d and h) for 14 h. The cells were then labeled with calcein acetoxymethyl ester and ethidium homodimer-1 (a–d) or stained with Hoechst 33258 (e–h) and visualized by fluorescence microscopy, as described in the Methods section. Photomicrographs are representative of at least three experiments for each experiment (acetoxymethyl ester and ethidium homodimer-1: magnification x 200; Hoechst 33258: magnification x 400). (B) The effect of calcium channel antagonists on myocyte apoptosis. Myocytes were treated with 10^–6 mol/l of doxorubicin in the presence or absence of either amlodipine (10^–9 to 10^–5 mol/l) or nifedipine (10^–6 mol/l) for 14 h. Fluorescent-stained nuclei of apoptotic myocytes were analyzed morphologically and expressed as the percentage of total nuclei, as described in Methods. Control myocytes were incubated in serum-deprived DMEM without any chemicals (n = 6). *p < 0.0001 vs. control. p < 0.0001 vs. doxorubicin.