4-aminopyridine causes apoptosis and blocks an outward rectifier K+ channel in malignant astrocytoma cell lines
✍ Scribed by Lawrence S. Chin; Charles C. Park; Kevin M. Zitnay; Manoj Sinha; Arthur J. DiPatri Jr.; Pablo Perillán; J. Marc Simard
- Book ID
- 101244442
- Publisher
- John Wiley and Sons
- Year
- 1997
- Tongue
- English
- Weight
- 86 KB
- Volume
- 48
- Category
- Article
- ISSN
- 0360-4012
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✦ Synopsis
Among the ion channels and pumps activated by growth factor stimulation, K 1 channels have been implicated in the growth and proliferation of several cancer cell lines. The role of these channels in central nervous system tumors, however, has not been described. This study used the 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 with wild-type p53 but not in A172 cells with mutant p53 (24-hr incubation with 4 mM 4-AP). In patch clamp experiments, we identified two types of K 1 currents in both cell lines, a charybdotoxin-sensitive Ca 21 -activated K 1 channel and a 4-AP-sensitive outward rectifier K 1 current. The outward rectifier current was blocked by 4-AP in a dose-dependent manner, with half-maximal block occurring at 3.9 mM. The blocking effect of 4 mM 4-AP was noticeable at potentials as low as 265 mV and was statistically significant at 260 mV and above, suggesting that 4-AP-sensitive current is active at physiological potentials. By contrast, charybdotoxin (1 µM) and tetraethylammonium • Cl (2 mM) blocked the Ca 21activated K 1 channel in both cell lines but had no appreciable effect on cell growth. Our findings reveal that 4-AP inhibits proliferation and the outward rectifier K 1 channel in both U87 and A172 cells. More studies are needed, however, to describe the mechanism by which K 1 channels influence proliferation and induce apoptosis.