Altered Na,K-ATPase pattern in γ-crystallin mutant mice

PURPOSE. Na,K-adenosine triphosphatase (ATPase) activity is elevated in the lenses of murine cataract Cryge^t and Cryge^ns mutant mice. In the present study, the expression of Na,K-ATPase α1, α2, and α3 catalytic subunit polypeptides was examined in the lenses of these mutant mice. METHODS. Membrane material was isolated from lenses and brain of 3-week-old wild-type mice, as well as heterozygous and homozygous mutant mice. Microsomal membranes were prepared by centrifugation of the homogenized material, and Na,K-ATPase polypeptides were detected by immunoblot analysis with antibodies directed against the Na,K-ATPase isoforms α1, α2, α2, and α3. RESULTS. For the Na,K-ATPase isoforms α2 and α3, membrane material obtained from the homozygous cataract mutants showed dense immunoblot bands that were not detected in material obtained from wild-type mice. An apparent increase of the α1 Na,K-ATPase isoform band density was also detected in lens material from the homozygous mutant mice. The Na,K-ATPase α3 polypeptide was also detected in lens membrane material obtained from heterozygous mice of both mutant strains. The α2 Na,K-ATPase polypeptide was observed in lens membrane material obtained from heterozygous Cryge^t mice, and a less dense band was detected in heterozygous Cryge^ns mice. Band densities of Na,K-ATPase subunits α1, α2, and α3 detected in brain membrane material were similar in both mutant and wild-type mice. CONCLUSIONS. The immunoblot results suggest that the abundance of Na,K-ATPase polypeptide is increased in the lens of the cataract mouse mutant but is not altered in the brain. The expression of the α2 and α3 isoform proteins of Na,K-ATPase is markedly upregulated in the cataractous lens.