4-AMINOPYRIDINE CAUSES APOPTOSIS AND BLOCKS AN OUTWARD RECTIFIER K-LINES( CHANNEL IN MALIGNANT ASTROCYTOMA CELL)

Among the ion channels and pumps activated by growth factor stimulatio n, K+ channels have been implicated in the growth and proliferation of several cancer cell lines. The role of these channels in central nerv ous system tumors, however, has not been described. This study used th e malignant astrocytoma cell lines U87 and A172, 4-Aminopyridine (4-AP ) inhibition of proliferation was dose dependent, and assessment using a TUNEL in situ assay revealed that apoptosis occurred in U87 cells w ith wild-type p53 but not in A172 cells with mutant p53 (24-hr incubat ion with 4 mM 4-AP). In patch clamp experiments, we identified two typ es of K+ currents in both cell lines, a charybdotoxin-sensitive Ca2(+) -activated K+ channel and a 4-AP-sensitive outward rectifier K+ curren t. The outward rectifier current was blocked by 4-AP in a dose-depende nt manner, with half-maximal block occurring at 3.9 mM. The blocking e ffect of 4 mM 4-AP was noticeable at potentials as low as -65 mV and w as statistically significant at -60 mV and above, suggesting that 4-AP -sensitive current is active at physiological potentials. By contrast, charybdotoxin (1 mu M) and tetraethylammonium . CI (2 mM) blocked the Ca2(+)-activated K+ channel in both cell lines but had no appreciable effect on cell growth. Our findings reveal that 4-AP inhibits prolife ration and the outward rectifier K+ channel in both U87 and A172 cells . More studies are needed, however, to describe the mechanism by which K+ channels influence proliferation and induce apoptosis. (C) 1997 Wi ley-Liss, Inc.