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 (1×10 ^-6, 1×10^-7, 1×10^-9 or 1×10^-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 1×10^-7 (20%) and 1×10^-9 M (15%). After 72 h, ONHA percentages increased significantly at all ET-1 concentrations (25%, 21%, 29%, 28% increases relative to vehicle, for 1×10^-6, 1×10^-7, 1×10^-9 and 1×10^-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.