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Thrombin inhibits active sodium-potassium transport in porcine lens.
Invest Ophthalmol Vis Sci. 1999 Aug; 40(9):2033-8.IO

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.

Authors+Show Affiliations

Department of Ophthalmology and Visual Sciences, University of Louisville School of Medicine, Kentucky 40202, USA.No affiliation info availableNo affiliation info available

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

10440258

Citation

Okafor, M C., et al. "Thrombin Inhibits Active Sodium-potassium Transport in Porcine Lens." Investigative Ophthalmology & Visual Science, vol. 40, no. 9, 1999, pp. 2033-8.
Okafor MC, Dean WL, Delamere NA. Thrombin inhibits active sodium-potassium transport in porcine lens. Invest Ophthalmol Vis Sci. 1999;40(9):2033-8.
Okafor, M. C., Dean, W. L., & Delamere, N. A. (1999). Thrombin inhibits active sodium-potassium transport in porcine lens. Investigative Ophthalmology & Visual Science, 40(9), 2033-8.
Okafor MC, Dean WL, Delamere NA. Thrombin Inhibits Active Sodium-potassium Transport in Porcine Lens. Invest Ophthalmol Vis Sci. 1999;40(9):2033-8. PubMed PMID: 10440258.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Thrombin inhibits active sodium-potassium transport in porcine lens. AU - Okafor,M C, AU - Dean,W L, AU - Delamere,N A, PY - 1999/8/10/pubmed PY - 1999/8/10/medline PY - 1999/8/10/entrez SP - 2033 EP - 8 JF - Investigative ophthalmology & visual science JO - Invest Ophthalmol Vis Sci VL - 40 IS - 9 N2 - 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. SN - 0146-0404 UR - https://www.unboundmedicine.com/medline/citation/10440258/Thrombin_inhibits_active_sodium_potassium_transport_in_porcine_lens_ DB - PRIME DP - Unbound Medicine ER -