Ca2+ influx mediates apoptosis induced by 4-aminopyridine, a K+ channel blocker, in HepG2 human hepatoblastoma cells

Apoptosis appears to be implicated in the pathogenesis and therapeutic appl ications of cancer. In this study we investigated the induction of apoptosi s by LF-aminopyridine (4-AP), a K+ channel blocker, and its mechanism in He pG2 human hepatoblastoma cells. 4-AP reduced cell viability and induced DNA fragmentation, a hallmark of apoptosis, in a dose-dependent manner. In add ition, 4-AP induced a sustained increase in intracellular Ca2+ concentratio n, which was completely inhibited by the extracellular Ca2+ chelation with EGTA. 4-AP also induced Mn2+ influx, indicating that the 4-AP-induced incre ased intracellular Ca2+ levels were due to activation of Ca2+ influx pathwa y. 4-AP also depolarized membrane potential that was measured by using di-O -C-5(3), a voltage-sensitive fluorescent dye. 4-AP-induced Ca2+ influx was significantly inhibited not by voltage-operative Ca2+ channel blockers (nif edipine or verapamil), but by flufenamic acid (FA), a known nonselective ca tion channel blocker. Quantitative analysis of apoptosis by the flow cytome try revealed that treatment with either FA or BAP-TA, an intracellular Ca2 chelator, significantly inhibited the 4-AP-induced apoptosis. Taken togeth er, these results suggest that the observed 4-AP-induced apoptosis in the H epG2 cells may result from Ca2+ influx through the activation of voltage-se nsitive Ca2+-permeable nonselective cation channels. These results further suggest that membrane potential change by modulation of K+ channel activity may be involved in the mechanism of apoptosis in human hepatoma cells. Cop yright (C) 2000 S. Karger AG, Basel.