The inhibitory influence of endothelin on active sodium-potassium transport in porcine lens

M. C. Okafor, Nicholas A Delamere

Research output: Contribution to journalArticle

16 Citations (Scopus)

Abstract

Purpose. Endothelin (ET)-1 is known to inhibit active NaK transport by as much as 50% in kidney tubule and other tissues. The presence of low levels of ET-1 in aqueous humor combined with the potential for release of ET-1 from ciliary processes suggests that the lens could be exposed to ET-1 in vivo. In this study, experiments were conducted to examine the influence of ET-1 on active NaK transport in porcine lens. Methods. The rate of Na,K-adenosine triphosphatase (Na,K-ATPase) dependent potassium transport was determined by measurements of ouabain-sensitive potassium (86Rb) uptake by intact lenses. Lens sodium content was measured by atomic absorption spectrophotometry. Cyclic adenosine monophosphate (cAMP) was measured by radioimmunoassay. Cytoplasmic calcium concentration in cultured porcine lens epithelium was measured by a fluorescence technique using fura-2. Results. In the presence of ET-1 (0.1 nM or higher concentration), the rate of ouabain-sensitive potassium (86Rb) uptake was diminished. The ET receptor antagonist PD145065 (2 μM) suppressed the inhibitory effect of ET-1 (100 nM) on 86Rb uptake. Sodium content was detectably increased in lenses exposed to ET-1 for 24 hours. Forskolin (1 μM) caused an eightfold increase of cAMP in the lens epithelium, but no increase of cAMP was detected in the epithelium of lenses treated with ET-1. Genistein (150 μM), an inhibitor of tyrosine kinases, abolished the inhibitory effects of ET-1 on lens 86Rb uptake. ET-1 caused an increase of cytoplasmic calcium concentration in cultured porcine lens epithelium. The cytoplasmic calcium response to ET-1 was inhibited by PD145065 and genistein. Conclusions. The results of the present study suggest that ET-1 causes inhibition of lens active Na-K transport by a mechanism that involves activation of ET receptors. Activation of ET receptors also causes an increase of cytoplasmic calcium concentration in cultured lens epithelial cells. Both responses to ET-1 appear to have a tyrosine kinase step, because they could be prevented by genistein. The physiological purpose of an ET-1-induced reduction in the rate of active Na-K transport by the lens is unknown at this time.

Original languageEnglish (US)
Pages (from-to)1018-1023
Number of pages6
JournalInvestigative Ophthalmology and Visual Science
Volume42
Issue number5
StatePublished - 2001
Externally publishedYes

Fingerprint

Endothelins
Endothelin-1
Lenses
Potassium
Swine
Sodium
Genistein
Epithelium
Cyclic AMP
Calcium
Endothelin Receptors
Active Biological Transport
Ouabain
Protein-Tyrosine Kinases
Kidney Tubules
Atomic Spectrophotometry
Aqueous Humor
Fura-2
Colforsin
Radioimmunoassay

ASJC Scopus subject areas

  • Ophthalmology

Cite this

The inhibitory influence of endothelin on active sodium-potassium transport in porcine lens. / Okafor, M. C.; Delamere, Nicholas A.

In: Investigative Ophthalmology and Visual Science, Vol. 42, No. 5, 2001, p. 1018-1023.

Research output: Contribution to journalArticle

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abstract = "Purpose. Endothelin (ET)-1 is known to inhibit active NaK transport by as much as 50{\%} in kidney tubule and other tissues. The presence of low levels of ET-1 in aqueous humor combined with the potential for release of ET-1 from ciliary processes suggests that the lens could be exposed to ET-1 in vivo. In this study, experiments were conducted to examine the influence of ET-1 on active NaK transport in porcine lens. Methods. The rate of Na,K-adenosine triphosphatase (Na,K-ATPase) dependent potassium transport was determined by measurements of ouabain-sensitive potassium (86Rb) uptake by intact lenses. Lens sodium content was measured by atomic absorption spectrophotometry. Cyclic adenosine monophosphate (cAMP) was measured by radioimmunoassay. Cytoplasmic calcium concentration in cultured porcine lens epithelium was measured by a fluorescence technique using fura-2. Results. In the presence of ET-1 (0.1 nM or higher concentration), the rate of ouabain-sensitive potassium (86Rb) uptake was diminished. The ET receptor antagonist PD145065 (2 μM) suppressed the inhibitory effect of ET-1 (100 nM) on 86Rb uptake. Sodium content was detectably increased in lenses exposed to ET-1 for 24 hours. Forskolin (1 μM) caused an eightfold increase of cAMP in the lens epithelium, but no increase of cAMP was detected in the epithelium of lenses treated with ET-1. Genistein (150 μM), an inhibitor of tyrosine kinases, abolished the inhibitory effects of ET-1 on lens 86Rb uptake. ET-1 caused an increase of cytoplasmic calcium concentration in cultured porcine lens epithelium. The cytoplasmic calcium response to ET-1 was inhibited by PD145065 and genistein. Conclusions. The results of the present study suggest that ET-1 causes inhibition of lens active Na-K transport by a mechanism that involves activation of ET receptors. Activation of ET receptors also causes an increase of cytoplasmic calcium concentration in cultured lens epithelial cells. Both responses to ET-1 appear to have a tyrosine kinase step, because they could be prevented by genistein. The physiological purpose of an ET-1-induced reduction in the rate of active Na-K transport by the lens is unknown at this time.",
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