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Na,K-ATPases of the lens epithelium and fiber cell: formation of catalytic cycle intermediates and Na+: K+ exchange.
Exp Eye Res. 1994 Jun; 58(6):705-18.EE

Abstract

Previous studies suggest that an alpha 2-related isoform of the catalytic subunit is predominant in the lens fiber cells. The alpha 1 isoform is predominant in the lens epithelium (Garner, Horwitz and Enomoto, 1992). Data are presented to show that strophanthidin-sensitive K+ transport is sustained by both of these lens Na,K-ATPases. The K50 for strophanthidin inhibition of K+ transport was 1.4 +/- 0.5 x 10(-6) M for the alpha 1 isoform of the epithelium, 1.3 +/- 0.6 x 10(-7) M for the alpha 2-related isoform of the lens fiber cells. Na+ accumulation in cultured bovine lenses was strophanthidin sensitive. The K50 values for strophanthidin-sensitive Na+ accumulation were similar to those obtained for K+ transport. ARP turnover by the lens fiber cell Na,K-ATPase (1700 +/- 600 min-1) was lower than ATP turnover by the lens epithelium Na,K-ATPase (8000 +/0 1000 min-1). Both lens Na,K-ATPases form the (ouabain + Mg(2+) + phosphate)-dependent phosphoenzyme. Both lens Na,K-ATPases form the (ATP + Na(+) + Mg2+)-dependent phosphorylated intermediate. K+ does not effectively dephosphorylate the Na,K-ATPase of the lens fibers. K+ does cause dephosphorylation of the Na,K-ATPase of the lens epithelium. Interaction of the Na,K-ATPase with Mg2+ would appear to cause the monovalent cation insensitivity. The lens fiber cell Na,K-ATPase, like the lens epithelium Na,K-ATPase occludes two K+ ions. However, between the two major Na,K-ATPases of the lens, there would appear to be differences in the ATP dissolution of the K-occluded state.

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Publisher Full Text

Authors+Show Affiliations

Garner MH
University of Texas Southwestern Medical Center at Dallas, Department of Ophthalmology 75235-8592.

MeSH

AnimalsBiological TransportCattleCulture TechniquesDose-Response Relationship, DrugHydrolysisLens, CrystallinePhosphorylationPotassiumRubidiumSodiumSodium-Potassium-Exchanging ATPaseStrophanthidin

Pub Type(s)

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

Language

eng

PubMed ID

7925710

Citation

Garner, M H.. "Na,K-ATPases of the Lens Epithelium and Fiber Cell: Formation of Catalytic Cycle Intermediates and Na+: K+ Exchange." Experimental Eye Research, vol. 58, no. 6, 1994, pp. 705-18.
Garner MH. Na,K-ATPases of the lens epithelium and fiber cell: formation of catalytic cycle intermediates and Na+: K+ exchange. Exp Eye Res. 1994;58(6):705-18.
Garner, M. H. (1994). Na,K-ATPases of the lens epithelium and fiber cell: formation of catalytic cycle intermediates and Na+: K+ exchange. Experimental Eye Research, 58(6), 705-18.
Garner MH. Na,K-ATPases of the Lens Epithelium and Fiber Cell: Formation of Catalytic Cycle Intermediates and Na+: K+ Exchange. Exp Eye Res. 1994;58(6):705-18. PubMed PMID: 7925710.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Na,K-ATPases of the lens epithelium and fiber cell: formation of catalytic cycle intermediates and Na+: K+ exchange. A1 - Garner,M H, PY - 1994/6/1/pubmed PY - 1994/6/1/medline PY - 1994/6/1/entrez SP - 705 EP - 18 JF - Experimental eye research JO - Exp Eye Res VL - 58 IS - 6 N2 - Previous studies suggest that an alpha 2-related isoform of the catalytic subunit is predominant in the lens fiber cells. The alpha 1 isoform is predominant in the lens epithelium (Garner, Horwitz and Enomoto, 1992). Data are presented to show that strophanthidin-sensitive K+ transport is sustained by both of these lens Na,K-ATPases. The K50 for strophanthidin inhibition of K+ transport was 1.4 +/- 0.5 x 10(-6) M for the alpha 1 isoform of the epithelium, 1.3 +/- 0.6 x 10(-7) M for the alpha 2-related isoform of the lens fiber cells. Na+ accumulation in cultured bovine lenses was strophanthidin sensitive. The K50 values for strophanthidin-sensitive Na+ accumulation were similar to those obtained for K+ transport. ARP turnover by the lens fiber cell Na,K-ATPase (1700 +/- 600 min-1) was lower than ATP turnover by the lens epithelium Na,K-ATPase (8000 +/0 1000 min-1). Both lens Na,K-ATPases form the (ouabain + Mg(2+) + phosphate)-dependent phosphoenzyme. Both lens Na,K-ATPases form the (ATP + Na(+) + Mg2+)-dependent phosphorylated intermediate. K+ does not effectively dephosphorylate the Na,K-ATPase of the lens fibers. K+ does cause dephosphorylation of the Na,K-ATPase of the lens epithelium. Interaction of the Na,K-ATPase with Mg2+ would appear to cause the monovalent cation insensitivity. The lens fiber cell Na,K-ATPase, like the lens epithelium Na,K-ATPase occludes two K+ ions. However, between the two major Na,K-ATPases of the lens, there would appear to be differences in the ATP dissolution of the K-occluded state. SN - 0014-4835 UR - https://www.unboundmedicine.com/medline/citation/7925710/NaK_ATPases_of_the_lens_epithelium_and_fiber_cell:_formation_of_catalytic_cycle_intermediates_and_Na+:_K+_exchange_ L2 - https://linkinghub.elsevier.com/retrieve/pii/S0014-4835(84)71068-2 DB - PRIME DP - Unbound Medicine ER -