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Regulation of Na,K-ATPase function in the lens.
J Exp Zool A Comp Exp Biol. 2003 Nov 01; 300(1):25-9.JE

Abstract

The two cell types in the lens, epithelium and fiber, have a very different specific activity of Na,K-ATPase; activity is much higher in the epithelium. However, judged by Western blot, fibers and epithelium express a similar amount of both Na,K-ATPase alpha and beta subunit proteins. Na,K-ATPase protein abundance does not tally with Na,K-ATPase activity. Studies were conducted to examine whether protein synthesis plays a role in maintenance of the high Na,K-ATPase activity in lens epithelium. An increase of cytoplasmic sodium was found to increase Na,K-ATPase protein expression in the epithelium, but not in the fibers. The findings illustrate the ability of lens epithelium to synthesize new Na,K-ATPase protein as a way to boost Na,K-ATPase in response to cell damage or pathological events. Methionine incorporation studies suggested Na,K-ATPase synthesis may also play a role in day to day preservation of high Na,K-ATPase activity. Na,K-ATPase protein in lens epithelial cells appeared to be continually synthesized and degraded. Experiments with cycloheximide suggest that specific activity of Na,K-ATPase in the lens epithelium may depend on the ability of the cells to continuously synthesize fresh Na,K-ATPase proteins. However, other factors such as phosphorylation of Na,K-ATPase alpha subunit may also influence Na,K-ATPase activity. When intact lenses were exposed to the agonist thrombin, Na,K-ATPase activity was diminished, but the response was suppressed by inhibitors of the Src family of non-receptor tyrosine kinases. Thrombin elicited tyrosine phosphorylation of lens epithelium membrane proteins, including a 100 kDa protein band thought to be the Na,K-ATPase alpha 1 subunit. It remains to be determined whether a tyrosine phosphorylation mechanism contributes to the low activity of Na,K-ATPase in lens fibers.

Authors+Show Affiliations

Department of Ophthalmology and Visual Sciences, University of Louisville, School of Medicine, Louisville, Kentucky 40292, USA. delamere@louisville. edu

Pub Type(s)

Comparative Study
Journal Article
Research Support, Non-U.S. Gov't
Research Support, U.S. Gov't, P.H.S.

Language

eng

PubMed ID

14598382

Citation

Delamere, Nicholas A.. "Regulation of Na,K-ATPase Function in the Lens." Journal of Experimental Zoology. Part A, Comparative Experimental Biology, vol. 300, no. 1, 2003, pp. 25-9.
Delamere NA. Regulation of Na,K-ATPase function in the lens. J Exp Zool A Comp Exp Biol. 2003;300(1):25-9.
Delamere, N. A. (2003). Regulation of Na,K-ATPase function in the lens. Journal of Experimental Zoology. Part A, Comparative Experimental Biology, 300(1), 25-9.
Delamere NA. Regulation of Na,K-ATPase Function in the Lens. J Exp Zool A Comp Exp Biol. 2003 Nov 1;300(1):25-9. PubMed PMID: 14598382.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Regulation of Na,K-ATPase function in the lens. A1 - Delamere,Nicholas A, PY - 2003/11/5/pubmed PY - 2004/1/22/medline PY - 2003/11/5/entrez SP - 25 EP - 9 JF - Journal of experimental zoology. Part A, Comparative experimental biology JO - J Exp Zool A Comp Exp Biol VL - 300 IS - 1 N2 - The two cell types in the lens, epithelium and fiber, have a very different specific activity of Na,K-ATPase; activity is much higher in the epithelium. However, judged by Western blot, fibers and epithelium express a similar amount of both Na,K-ATPase alpha and beta subunit proteins. Na,K-ATPase protein abundance does not tally with Na,K-ATPase activity. Studies were conducted to examine whether protein synthesis plays a role in maintenance of the high Na,K-ATPase activity in lens epithelium. An increase of cytoplasmic sodium was found to increase Na,K-ATPase protein expression in the epithelium, but not in the fibers. The findings illustrate the ability of lens epithelium to synthesize new Na,K-ATPase protein as a way to boost Na,K-ATPase in response to cell damage or pathological events. Methionine incorporation studies suggested Na,K-ATPase synthesis may also play a role in day to day preservation of high Na,K-ATPase activity. Na,K-ATPase protein in lens epithelial cells appeared to be continually synthesized and degraded. Experiments with cycloheximide suggest that specific activity of Na,K-ATPase in the lens epithelium may depend on the ability of the cells to continuously synthesize fresh Na,K-ATPase proteins. However, other factors such as phosphorylation of Na,K-ATPase alpha subunit may also influence Na,K-ATPase activity. When intact lenses were exposed to the agonist thrombin, Na,K-ATPase activity was diminished, but the response was suppressed by inhibitors of the Src family of non-receptor tyrosine kinases. Thrombin elicited tyrosine phosphorylation of lens epithelium membrane proteins, including a 100 kDa protein band thought to be the Na,K-ATPase alpha 1 subunit. It remains to be determined whether a tyrosine phosphorylation mechanism contributes to the low activity of Na,K-ATPase in lens fibers. SN - 1548-8969 UR - https://www.unboundmedicine.com/medline/citation/14598382/Regulation_of_NaK_ATPase_function_in_the_lens_ L2 - https://doi.org/10.1002/jez.a.10305 DB - PRIME DP - Unbound Medicine ER -