Depolarization-induced ⁶⁵zinc influx into cultured cortical neurons

Toxic Zn²⁺ influx may be a key mechanism underlying selective neuronal death after transient global ischemia in rats. To identify routes responsible for neuronal Zn²⁺ influx, we measured the accumulation of ⁶⁵Zn²⁺ into cultured murine cortical cells under depolarizing conditions (60 mM K⁶) associated with severe hypoxia-ischemia in brain tissue. Addition of 60 mM K⁺ or 300 μM kainate substantially increased ⁶⁵Zn²⁺ accumulation into mixed cultures of neurons and glia, but not glia alone. ⁶⁵Zn²⁺ accumulation was attenuated by increasing concentrations of extracellular Ca²⁺ or trypsin pretreatment, but not by late trypsinization, and corresponded to an increase in atomic Zn²⁺. Confirming predominantly neuronal entry, K⁺-induced ⁶⁵Zn²⁺ accumulation was reduced by prior selective destruction of neurons with NMDA. K⁺-induced ⁶⁵Zn²⁺ influx was not sensitive to glutamate receptor antagonists, but was attenuated by Gd³⁺ and Cd²⁺ as well as 1 μM nimodipine; it was partially sensitive to 1 μM ω-conotoxin-GVIA, and insensitive to 1 μM ω-agatoxin-IVA. K⁺-induced, Gd³⁺-sensitive ⁴⁵Ca²⁺ accumulation but not ⁶⁵Zn²⁺ accumulation was sharply attenuated by lowering extracellular pH to 6.6.