Zn2+ influx is critical for some forms of spreading depression in brain slices.
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Spreading depression (SD) is wave of profound depolarization that propagates throughout brain tissue and can contribute to the spread of injury after stroke or traumatic insults. The contribution of Ca(2+) influx to SD differs depending on the stimulus, and we show here that Zn(2+) can play a critical complementary role in murine hippocampal slices. In initial studies, we used the Na(+)/K(+) ATPase inhibitor ouabain and found conditions in which SD was always prevented by L-type Ca(2+) channel blockers; however, Ca(2+) influx was not responsible for L-type effects. Cytosolic Ca(2+) increases were not detectable in CA1 neurons before SD, and removal of extracellular Ca(2+) did not prevent ouabain-SD. In contrast, cytosolic Zn(2+) increases were observed in CA1 neurons before ouabain-SD, and L-type channel block prevented the intracellular Zn(2+) rises. A slow mitochondrial depolarization observed before ouabain-SD was abolished by L-type channel block, and Zn(2+) accumulation contributed substantially to initial mitochondrial depolarizations. Selective chelation of Zn(2+) with N,N,N',N'-tetrakis(2-pyridylmethyl)ethylenediamine (TPEN) abolished SD, implying that Zn(2+) entry can play a critical role in the generation of ouabain-SD. TPEN was most effective when synaptic activity was reduced by adenosine A(1) receptor activation, and a combination of Ca(2+) and Zn(2+) removal was required to prevent ouabain-SD when A(1) receptors were blocked. Similarly, Zn(2+) chelation could prevent SD triggered by oxygen/glucose deprivation but Zn(2+) accumulation did not contribute to SD triggered by localized high K(+) exposures. These results identify Zn(2+) as a new target for the block of spreading depolarizations after brain injury.