HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) Submit a response Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Okafor, M. C. Articles by Delamere, N. A. Search for Related Content PubMed PubMed Citation Articles by Okafor, M. C. Articles by Delamere, N. A.

Thrombin Inhibits Active Sodium–Potassium Transport In Porcine Lens

¹ From the Department of Ophthalmology and Visual Sciences, ² Department of Biochemistry, and ³ Department of Pharmacology and Toxicology, University of Louisville School of Medicine, Louisville, Kentucky.

Abstract

PURPOSE. Although thrombin is best known for its role in blood coagulation, it has been reported to change the activity of ion motive ATPases in some tissues. In the present study, experiments were conducted to determine the influence of thrombin on active sodium–potassium transport in porcine lenses.

METHODS. Ouabain-sensitive potassium (⁸⁶Rb) uptake by intact porcine lenses was used as an index of Na,K-ATPase–mediated active sodium–potassium transport. Na,K-ATPase activity was measured by determining ouabain-sensitive ATP hydrolysis in isolated membrane material.

RESULTS. In the presence of thrombin (1 unit/ml) the rate of ouabain-sensitive potassium (⁸⁶Rb) uptake was reduced by 40% to 60%, but ouabain-insensitive potassium (⁸⁶Rb) uptake was unchanged. The inhibitory effect of thrombin on ouabain-sensitive potassium (⁸⁶Rb) uptake was suppressed in the presence of hirudin (an antagonist for thrombin receptors) but persisted in the presence of amphotericin B (a pseudo ionophore that effectively clamps plasma membrane sodium permeability at a high value). Enzyme measurements showed ouabain-sensitive ATP hydrolysis (Na,K-ATPase activity) was significantly inhibited in membrane material isolated from the capsule-epithelium of lenses, which had been pretreated with thrombin for 30 minutes. However, thrombin failed to exert a direct inhibitory effect on Na,K-ATPase activity when added directly to membrane fragments isolated from the epithelium of control (nonincubated) lenses. Both genistein and herbimycin (tyrosine kinase inhibitors) suppressed the effect of thrombin on the ⁸⁶Rb uptake response. Results from Western blot studies suggested that tyrosine kinases are activated in the epithelium of lenses exposed to thrombin.

CONCLUSIONS. The results suggest the inhibitory effect of thrombin on lens active sodium–potassium transport could involve the activation of a receptor–second-messenger mechanism in intact lens cells. The response appears to involve a tyrosine kinase–mediated step. The functional significance of the thrombin-mediated change of lens active sodium–potassium transport is unclear since appreciable amounts of thrombin may only be presented to the lens during instances of blood-aqueous–barrier breakdown. It is possible that lens receptors are functionally activated by other proteases, possibly cathepsins, which may enter aqueous humor from the ciliary body.

This article has been cited by other articles:

				S. Tamiya, M. C. Okafor, and N. A. Delamere Purinergic agonists stimulate lens Na-K-ATPase-mediated transport via a Src tyrosine kinase-dependent pathway Am J Physiol Cell Physiol, August 1, 2007; 293(2): C790 - C796. [Abstract] [Full Text] [PDF]

				S. Matalon and S. I. Rennard Thrombin Increases Lung Water by Decreasing Na,K-ATPase Activity Am. J. Respir. Cell Mol. Biol., October 1, 2005; 33(4): 317 - 318. [Full Text] [PDF]

				C. James, D. J. Collison, and G. Duncan Characterization and Functional Activity of Thrombin Receptors in the Human Lens Invest. Ophthalmol. Vis. Sci., March 1, 2005; 46(3): 925 - 932. [Abstract] [Full Text] [PDF]

				L. D. Bozulic, W. L. Dean, and N. A. Delamere The Influence of SRC-Family Tyrosine Kinases on Na,K-ATPase Activity in Lens Epithelium Invest. Ophthalmol. Vis. Sci., February 1, 2005; 46(2): 618 - 622. [Abstract] [Full Text] [PDF]

				L. D. Bozulic, W. L. Dean, and N. A. Delamere The influence of Lyn kinase on Na,K-ATPase in porcine lens epithelium Am J Physiol Cell Physiol, January 1, 2004; 286(1): C90 - C96. [Abstract] [Full Text] [PDF]

				S. Tamiya, W. L. Dean, C. A. Paterson, and N. A. Delamere Regional Distribution of Na,K-ATPase Activity in Porcine Lens Epithelium Invest. Ophthalmol. Vis. Sci., October 1, 2003; 44(10): 4395 - 4399. [Abstract] [Full Text] [PDF]

				M. C. Okafor, P. Mukhopadhyay, and N. A. Delamere Studies on Endothelin Release and Na,K Transport in Porcine Lens Invest. Ophthalmol. Vis. Sci., March 1, 2002; 43(3): 790 - 796. [Abstract] [Full Text] [PDF]

				M. C. Okafor and N. A. Delamere The Inhibitory Influence of Endothelin on Active Sodium-Potassium Transport in Porcine Lens Invest. Ophthalmol. Vis. Sci., April 1, 2001; 42(5): 1018 - 1023. [Abstract] [Full Text]