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 alpha1, alpha2, and alpha3 catalytic subunit polypeptides was examined in the lenses of these mutant mice.
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 alpha1, alpha2, and alpha3.
For the Na,K-ATPase isoforms alpha2 and alpha3, 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 alpha1 Na,K-ATPase isoform band density was also detected in lens material from the homozygous mutant mice. The Na,K-ATPase alpha3 polypeptide was also detected in lens membrane material obtained from heterozygous mice of both mutant strains. The alpha2 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 alpha1, alpha2, and alpha3 detected in brain membrane material were similar in both mutant and wild-type mice.
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 alpha2 and alpha3 isoform proteins of Na,K-ATPase is markedly upregulated in the cataractous lens.