ABSTRACT
The role of endothelin-1 (ET-1) a potent vasoactive peptide, in glaucoma pathogenesis is receiving increasing attention, particularly in astroglial activation in optic nerve damage. Our laboratory has also shown that ET-1 treatment causes proliferation of cultured human optic nerve head astrocytes to possibly initiate astrogliosis. ET-1 is distributed in retina, optic nerve, and ciliary epithelium, however the effects of elevated intraocular pressure (IOP) (as seen in glaucoma) on ET-1 and ET(B) receptors are not clearly understood. In the present study, the levels of immunoreactive ET-1 (ir-ET-1) in aqueous humour (AH) and optic nerve head (ONH) were determined in the Morrison elevated IOP model of glaucoma. Additionally in the ONH of these rats, immunohistochemical analyses of ET(B) receptors and glial fibrillary acidic protein (GFAP; a marker for astroglial cells and for astrogliosis) were performed. There was 2- to 2.5-fold increase in AH ir-ET-1 levels for rats subjected to elevated IOP, compared to their respective controls. In the Morrison rat model of glaucoma, elevated IOP increased optic nerve ir-ET-1 with concomitant increases in ir-ET(B) and ir-GFAP labelling (possibly indicative of astrogliosis and hypertrophy). As seen in brain astrocytes subjected to neurotrauma, the present findings are suggestive of ET-1's role in astroglial activation, particularly in response to elevated IOP in glaucoma.
Subject(s)
Disease Models, Animal , Endothelin-1/metabolism , Glaucoma/metabolism , Intraocular Pressure/physiology , Animals , Endothelin-1/physiology , Glaucoma/chemically induced , Intraocular Pressure/drug effects , Male , Rats , Rats, Inbred BN , Saline Solution, Hypertonic/pharmacologyABSTRACT
Endothelin-1 (ET-1) (1-100 nM) decreases the activity of Na,K-ATPase, a key enzyme responsible for aqueous humor formation, in transformed human non-pigmented ciliary epithelial (HNPE) cells. The present study sought to determine if ET-1 alters the expression of the catalytically active alpha subunit of Na,K-ATPase in HNPE cells and identify mechanisms underlying these effects. We report that acute (15 and 30 min) treatment with ET-1 results in an increase in mRNA expression of the alpha 1 subunit of Na,K-ATPase. Similar to ET-1's effects, ouabain (100 microM), a selective inhibitor of Na,K-ATPase, and monensin (10 microM), a sodium ionophore, also increased Na,K-ATPase expression in HNPE cells. The increase in Na,K-ATPase expression by short-term treatment with ouabain and monensin was dependent on their ability to elevate intracellular sodium concentrations. However, acute ET-1 treatment mediated increase in Na,K-ATPase expression was independent of changes in intracellular sodium. A prolonged (24 hr) ET-1 treatment results in an increase in both mRNA and protein levels of the alpha 1 subunit of Na,K-ATPase. These observations suggest that ET-1 could play a homeostatic role in modulating aqueous humor formation by having differential effects on the activity and expression of Na,K-ATPase by the ciliary epithelium in the eye.