Vladimir Matchkov

Familial hemiplegic migraine type 2 (FHM2) is migraine with aura that is associated with mutations in the Na, K-ATPase α2 isoform including G301R mutation. These FHM2-associated mutations result in reduced expression of the α2 Na, K-ATPase. Migraine attack in FHM2 patients is characterized by sequential hypo- and hyperperfusion of the affected hemisphere. Heterozygote mice bearing G301R mutation (α2+/−G301R) phenocopy several FHM2-relevant disease traits.

We hypothesize that α2+/−G301R mice have abnormal neurovascular coupling.

We tested this hypothesis by comparing α2+/−G301R and wild type (WT) mice. The sex difference was considered. Increase in sensory cortex perfusion in response to whiskers stimulation was compared in anaesthetized mice using Laser Speckle imaging. In brain slices loaded with Calcium Green-1, we assessed parenchymal artery diameter and intracellular Ca2+ changes in astrocytic endfeet in response to neuronal excitation by electric field stimulation (EFS). Isolated middle cerebral arteries were studied in isometric myograph for wall tension changes in response to elevation of bath K+. Smooth muscle membrane potential was assessed with sharp electrode impalements. Quantitative PCR, Western blot and whole mount immunohistochemistry were used to study the molecular background for the functional changes.

Whisker stimulation induced a larger increase in blood flow in the sensory cortex of α2+/−G301R mice than in WT mice. Moreover, the response was larger in male than female α2+/−G301R mice but no significant differences between male and female WT mice was seen. EFS was associated with larger parenchymal artery dilation in brain slices from α2+/−G301R mice than in WT mice. EFS-induced vasodilation was inhibited by 100 μM BaCl2, suggesting involvement of inward-rectifying K+ channels (Kir). The EFS induced increase in astrocytic intracellular Ca2+ was similar in α2+/−G301R and WT mice. No sex differences in brain slice responses were found. Isolated middle cerebral arteries from α2+/−G301R mice had larger relaxation to elevated bath K+ than similar arteries from WT mice. Removal of endothelium suppressed the relaxations of arteries from α2+/−G301R mice and eliminated the difference between groups. This relaxation was inhibited by BaCl2. Expression of Kir2.1 channels was higher in endothelium of arteries from α2+/−G301R mice than in WT while the expression in smooth muscle cells was not changed.

These data suggest that abnormal neurovascular coupling in mice bearing the FHM2-associated mutation is a result of increased endothelial Kir2.1 channel expression. Such changes may underlie the abnormal vascular hyperperfusion in FHM2 patients during migraine attack.