Hypercontractile Cardiac Phenotype in Mice with Migraine-Associated Mutation in the Na + ,K + -ATPase α 2 -Isoform.

Two α-isoforms of the Na ⁺ ,K ⁺ -ATPase (α ₁ and α ₂ ) are expressed in the cardiovascular system, and it is unclear which isoform is the preferential regulator of contractility. Mice heterozygous for the familial hemiplegic migraine type 2 (FHM2) associated mutation in the α ₂ -isoform (G301R; α ₂ ^+/G301R mice) have decreased expression of cardiac α ₂ -isoform but elevated expression of the α ₁ -isoform. We aimed to investigate the contribution of the α ₂ -isoform function to the cardiac phenotype of α ₂ ^+/G301R hearts. We hypothesized that α ₂ ^+/G301R hearts exhibit greater contractility due to reduced expression of cardiac α ₂ -isoform. Variables for contractility and relaxation of isolated hearts were assessed in the Langendorff system without and in the presence of ouabain (1 µM). Atrial pacing was performed to investigate rate-dependent changes. The α ₂ ^+/G301R hearts displayed greater contractility than WT hearts during sinus rhythm, which was rate-dependent. The inotropic effect of ouabain was more augmented in α ₂ ^+/G301R hearts than in WT hearts during sinus rhythm and atrial pacing. In conclusion, cardiac contractility was greater in α ₂ ^+/G301R hearts than in WT hearts under resting conditions. The inotropic effect of ouabain was rate-independent and enhanced in α ₂ ^+/G301R hearts, which was associated with increased systolic work.