Submitted on October 21, 2008
Revised on April 29, 2009
Accepted on May 1, 2009
Elevated hydrostatic pressure activates sodium-hydrogen exchanger-1 in rat optic nerve head astrocytes
Amritlal Mandal1, Mohammad Shahidullah1*, Nicholas A Delamere1, and Marcos A Teran1
1 University of Arizona
* To whom correspondence should be addressed. E-mail: shahidua{at}email.arizona.edu.
Optic nerve head astrocytes become abnormal in eyes that have elevated intraocular pressure and cultured astrocytes display altered protein expression after being subjected 1 or more days to elevated hydrostatic pressure. Here we show 2 h elevated hydrostatic pressure (15 or 30 mmHg) causes phosphorylation of ERK1/2, ribosomal S6 protein kinase (p90RSK), and Na-H exchanger-1 (NHE1) in cultured rat optic nerve head astrocytes as judged by western blot analysis. The MEK/ERK inhibitor U0126 abolished phosphorylation of NHE1 and p90RSK as well as ERK1/2. To examine NHE1 activity, cytoplasmic pH (pHi) was measured using BCECF and, in some experiments, cells were acidified by 5 min exposure to 20 mM ammonium chloride. Although baseline pHi was unaltered, the rate of pHi recovery from acidification was four fold higher in pressure-treated astrocytes. In the presence of either U0126 or dimethylamiloride (DMA), an NHE inhibitor, hydrostatic pressure did not change the rate of pHi recovery. The findings are consistent with NHE1 activation due to phosphorylation of ERK1/2, p90RSK and NHE1 that occurs in response to hydrostatic pressure. These responses may precede long term changes of protein expression known to occur in pressure-stressed astrocytes.
