Elevated Hydrostatic Pressure Activates Sodium‐Hydrogen Exchanger‐1 in Rat Optic Nerve Head Astrocytes

Abstract

ObjectiveOptic nerve head (ONH) astrocytes are thought to involve in the degeneration of ganglion cells and remodeling of surrounding extracellular matrix in glaucoma. Elevated intraocular pressure (IOP) is the main glaucoma risk factor. Here we report altered sodium hydrogen exchange (NHE) activity in cells exposed to elevated hydrostatic pressure .MethodsHydorstatic pressure (HP) of 15 mmHg was applied to the cells in a 20 cm glass cylinder filled with the culture medium equilibrated with 5% CO2/95% air for 2h. Proteins were analyzed by Western blot and cytoplasmic pH (pHi) was measured by BCECF ratiometry.ResultsElevated HP causes phosphorylation of ERK1/2, ribosomal S6 kinase (p90RSK), and Na‐H exchanger‐1 (NHE1). The MEK/ERK inhibitor UO126 abolished phosphorylation of NHE1 and p90RSK as well as ERK1/2. Although baseline pHi was unaltered in pressure treated cells, the rate of pHi recovery from ammonium chloride acidification was four fold higher. Dimethylamiloride (DMA), an NHE inhibitor, abolished and U0126 partially inhibited the increased rate of pHi recovery in pressure treated astrocytes.ConclusionsThe findings suggest elevated HP caused NHE‐1 activation through phosphorylation following activation of ERK1/2 and p90RSK. These events may lead to the long term changes of protein expression known to occur in pressure‐stressed astrocytes.FundingNIH Grant EY014069