Block of Na+,K+-ATPase and induction of hybrid death by 4-aminopyridine in cultured cortical neurons

K+ channel blockers such as 4-aminopyridine (4-AP) can be toxic to neurons; the cellular mechanism underlying the toxicity, however, is obscure. In cultured mouse cortical neurons, we tested the hypothesis that the toxic effect of 4-AP might result from inhibiting the Na+, K+-ATPase (Na+, K+-pump) and thereafter induction of a hybrid death of concomitant apoptosis and necrosis. The Na+, K+-pump activity, monitored as whole-cell membrane currents, was markedly blocked by 4-AP in concentration- and voltage-dependent manners in low millimolar ranges. At similar concentrations, 4-AP induced a neuronal death sensitive to attenuation by the caspase inhibitor Z-VAD-FMK (Z-Val-Ala-Asp(OMe)-fluoromethyl ketone) or Ca2+ chelator BAPTA-AM (1,2-bis(2-aminophenoxy) ethane-N, N, N', N'-tetraacetic acid-acetoxymethyl ester). Electron microscopy confirmed hybrid ultrastructural features of coexisting apoptotic and necrotic components in same cells. We suggest that 4-AP is a potent antagonist of the Na+, K+-ATPase and an inducer of the hybrid death of central neurons.