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M. Shahidullah, N. A. Delamere; Activation of Src Family Kinases Causes Inhibition of Na,K-ATPase Activity in Porcine Nonpigmented Ciliary Epithelium. Invest. Ophthalmol. Vis. Sci. 2010;51(13):690.
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Nonpigmented ciliary epithelium (NPE) is the tissue responsible for aqueous humor secretion in the eye. Na,K-ATPase is pivotal in the secretion of this fluid. Src family kinases (SFK) have been shown to influence Na,K-ATPase activity in porcine ocular lens epithelium (Bozulic, Dean et al. 2005). Here we show that activation of SFK by DIDS, SNP or by lowering cytoplasmic pH inhibits Na,K-ATPase activity.
Src activation in porcine NPE lysate was detected by western blot followed by densiometric analysis. Na,K-ATPase activity was studied in porcine cultured NPE by measuring ouabain-sensitive potassium (86Rb) uptake.
Sodium nitroprusside (100 µM), DIDS (100 µM) and low pH (6.5) bathing medium caused significant phosphorylation of Src and ERK1/2. The Src phosphorylation was abolished by pre-treating the cells with a selective Src family kinases inhibitor, PP2. Interestingly, PP2 also blocked DIDS-induced ERK1/2 phophorylation, indicating that Src phosphorylation was the precedeing event. Sodium nitroprusside, DIDS and low pH bathing medium caused marked inhibition of Na,K-ATPase activity as measured by the reduction of ouabain-sensitive potassium (86Rb) uptake in cultured NPE. DIDS-induced inhibition of Na,K-ATPase activity was blocked by PP2. DIDS or low pH medium caused significant reduction of cytoplasmic pH.
Activation of Src family kinases causes inhibition of Na,K-ATPase activity in NPE. Lowering cytoplasmic pH may have the potential to activate Src family kinases. Acid activation of Src family kinases can be a novel way of controlling fluid secretion in the NPE and possibly in other epithelia.ReferenceBozulic, L. D., W. L. Dean, et al. (2005). "The influence of SRC-family tyrosine kinases on Na,K-ATPase activity in lens epithelium." Investigative Ophthalmology & Visual Science 46(2): 618-622.
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