Zn²⁺Influx Is Critical for Some Forms of Spreading Depression in Brain Slices

Abstract

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.