P 361
Genistein inhibits NaKCl cotransport activity in ciliary epithelial cells
D. Hochgesand, A. J. Augustin, N. Pfeiffer
Introduction: NaKCl cotransport is an elctroneutral ion transport mechanism, which contributes to fluid flow in various tissues. Recent studies demonstrated that NaKCl cotransport plays an important role for blood to aqueous net chlorid transport. Genistein, a tyrosine kinase inhibitor, acts on cotransport activity f.e. in fibroblasts or endothelial cells. Here we examined the influence of genistein on cotransport activity in ciliary epithelium.
Methods: Studies were done using fetal human pigmented ciliary epithelial cells. Cotransport activity was measured by rubidium uptake using radioactive rubidium as a marker for potassium.
Results: Cotransport activity was inhibited by 40% after exposure of cells for 10 min with 10-4 M genistein. This effect was dose-dependent. No effect of genistein could be found on NaK-ATPase. The effect of tyrphostin and herbimycin on cotransport activity was less. Genistein did not block stimulation of cotransport by isoproterenol (b -adrenergic agonist) or calyculin A (inhibitor of protein phosphatase). Inhibition of cotransport by genistein was partially additive with inhibition by phorbol-myristate-acetate (PMA).
Discussion: Tyrosin kinases are involved in regulation of NaKCl cotransport activity in ciliary epithelial cells along with previously known protein kinase C (PKC), protein phophatase and cAMP-cascade. Inhibition of tyrosin kinase by genistein results in the cell culture model in a marked reduction of cotransport activity. Genistein is a possible candidate for inhibtion of aqueous humor production, since NaKCl cotransport contributes to blood to aqueous ion transport
Department of Ophthalmology, University of Mainz, Langenbeckstr.1, D-55101 Mainz, Germany .