Effect of apoptosis-related compounds on Ca2+ transport system in isolated rat liver nuclei.

The effect of various inhibitors of DNA topoisomerase II, which has been shown to induce apoptotic cell death, on Ca2+ transport in isolated rat liver nuclei was investigated. Ca2+ uptake and release were determined with a Ca2+ electrode. The presence of aurintricarboxylic acid (ATA; 10(-6) to 10(-4) M), etoposide (10(-4) M), genistein (10(-5) and 10(-4) M) or amsacrine (10(-4) M) in the reaction mixture caused a significant increase in Ca2+ release from the nuclei. Also, these compounds (10(-4) M) significantly inhibited Ca2+ uptake by the nuclei. However, the presence of ATA (10(-5) and 10(-4) M) in the enzyme reaction mixture did not significantly inhibit Ca2+-ATPase activity, which is involved in the nuclear Ca2+ uptake, in the liver nuclei, while etoposide (10(-4) M), genistein (10(-4) M) and amsacrine (10(-4) M) appreciably decreased the enzyme activity. Meanwhile, addition of Ca2+ clearly activated DNA fragmentation in the liver nuclei. The Ca2+ activated DNA fragmentation was significantly prevented by the presence of etoposide, genistein and amsacrine with the concentrations of 10(-5) and 10(-4) M in the reaction mixture, although ATA (10(-5) and 10(-4) M) had no effect. The present study demonstrates that some apoptosis inducible compounds used can influence on Ca2+ transport system in isolated rat liver nuclei, suggesting a decrease of nuclear Ca2+ level involved in nuclear functions.