The role of endothelin-1 and its receptors in optic nerve head astrocyte proliferation

Aim To characterise the influence of endothelin-1 (ET-1), a vasoactive peptide, and its receptors (endothelin B (ETB) and endothelin A (ETA)) on rat optic nerve head astrocyte (ONHA) proliferation. Methods ONHAs were isolated from adult Brown Norway rats. ONHA specificity was determined with immunohistochemistry for: glial fibrillary acidic protein (GFAP); A2B5, a marker of type II astrocytes located outside the ONH; and myelin basic protein (MBP). ONHA proliferation was quantified following treatment with ET-1 (1 x 10(-6), 1 x 10(-7), 1 x 10(-9) or 1 x 10(-11) M) or vehicle for 24, 48 or 72 h. ETB and ETA antagonists were used to assess the role of each receptor in ONHA proliferation. Results ONHA specificity was confirmed with positive labelling for GFAP, and negative labelling for A2B5 and MBP. ONHAs also expressed ETB and ETA. Cell percentages increased significantly beginning 48 h after ET-1 exposure with 1 x 10(-7) (20%) and 1 x 10(-9) M (15%). After 72 h, ONHA percentages increased significantly at all ET-1 concentrations (25%, 21%, 29%, 28% increases relative to vehicle, for 1 x 10(-6), 1 x 10(-7), 1 x 10(-9) and 1 x 10(-11) M, respectively). No significant proliferation occurred in the presence of either antagonist. Conclusion ONHAs proliferated following 48 h or more of exposure to ET-1. The proliferation required both ETB and ETA receptors.