Purpose. The lens epithelium is thought to conduct Na-K transport for the entire lens cell mass. Lens fibers have a poor ion transport capacity. The authors tested whether different Na,K-ATPase polypeptides are expressed in the two cell types and whether both cells have the machinery needed for ongoing Na,K-ATPase expression as judged by the presence of mRNA for the Na,K-ATPase α subunit. Methods. Membranes were isolated from adult rat lens epithelium or fibers, and Western blot experiments were conducted for Na,K- ATPase α1, α2, and α3 polypeptides. Total RNA was isolated from adult rat lens epithelium or fiber cells, and Northern analysis was conducted for Na,K-ATPase α1, α2, and α3 mRNA. Some experiments were conducted using fiber cells from neonatal (3-day-old) rat lenses. Results. Multiple isoforms of Na,K-ATPase were detected in adult rat lens epithelium. Judged by Northern blot band intensity, mRNA for Na,K-ATPase α1 and α2 was more abundant than for α3 mRNA. By Western blot, Na,K-ATPase α1, α2, and α3 polypeptides were observed as sharp bands at 100 to 108 kDa. In fiber cells, only Na,K-ATPase α1 immunoreactive polypeptide was detected. Judged by immunoblot density, the amount of α1 polypeptide was similar in both epithelium and fiber cell material. However, Na,K-ATPase α subunit mRNA was not found in adult lens fibers. To test whether Na,K-ATPase synthesis takes place during fiber cell growth. Northern blot analysis was conducted with mRNA from neonatal (3-day-old) lens fibers: Na,K-ATPase α1 mRNA was clearly visible. Conclusions. Adult rat lens epithelium expresses more than one isoform of Na,K-ATPase catalytic subunit, whereas only the α1 isoform can be detected in fiber cells. In adult rat lens fiber cells, the observation of α1 polypeptide, but no α1 mRNA, suggests that ongoing α1 synthesis is low. Based on the detection of α1 mRNA in neonatal lens fibers, Na,K-ATPase synthesis by lens fibers may be higher during cell elongation and growth.
|Original language||English (US)|
|Number of pages||7|
|Journal||Investigative Ophthalmology and Visual Science|
|Publication status||Published - Jul 1996|
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