July 1996
Volume 37, Issue 8
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Articles  |   July 1996
Isoforms of Na,K-ATPase in rat lens epithelium and fiber cells.
Author Affiliations
  • A E Moseley
    Department of Biochemistry, University of Louisville, Kentucky, USA.
  • W L Dean
    Department of Biochemistry, University of Louisville, Kentucky, USA.
  • N A Delamere
    Department of Biochemistry, University of Louisville, Kentucky, USA.
Investigative Ophthalmology & Visual Science July 1996, Vol.37, 1502-1508. doi:
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      A E Moseley, W L Dean, N A Delamere; Isoforms of Na,K-ATPase in rat lens epithelium and fiber cells.. Invest. Ophthalmol. Vis. Sci. 1996;37(8):1502-1508.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract

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 alpha subunit. METHODS: Membranes were isolated from adult rat lens epithelium or fibers, and Western blot experiments were conducted for Na,K-ATPase alpha 1, alpha 2, and alpha 3 polypeptides. Total RNA was isolated from adult rat lens epithelium or fiber cells, and Northern analysis was conducted for Na,K-ATPase alpha 1, alpha 2, and alpha 3 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 alpha 1 and alpha 2 was more abundant than for alpha 3 mRNA. By Western blot, Na,K-ATPase alpha 1, alpha 2, and alpha 3 polypeptides were observed as sharp bands at 100 to 108 kDa. In fiber cells, only Na,K-ATPase alpha 1 immunoreactive polypeptide was detected. Judged by immunoblot density, the amount of alpha 1 polypeptide was similar in both epithelium and fiber cell material. However, Na,K-ATPase alpha 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 RNA from neonatal (3-day-old) lens fibers; Na,K-ATPase alpha 1 mRNA was clearly visible. CONCLUSIONS: Adult rat lens epithelium expresses more than one isoform of Na,K-ATPase catalytic subunit, whereas only the alpha 1 isoform can be detected in fiber cells. In adult rat lens fiber cells, the observation of alpha 1 polypeptide, but no alpha 1 mRNA, suggests that ongoing alpha 1 synthesis is low. Based on the detection of alpha 1 mRNA in neonatal lens fibers, Na,K-ATPase synthesis by lens fibers may be higher during cell elongation and growth.

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