Abstract
Abstract: :
Purpose:Alpha–2 adrenoceptor agonists have been reported to be protective in a number of retinal injury models. Upon administration of these agents, extracellular signal–regulated kinases (ERKs) are significantly phosphorylated in the Muller cell layer. As the activation of ERKs have been associated with cell survival signals, it has been proposed that activation of the ERK pathway in Muller cells plays a role in the neuroprotective effects of these alpha–2 agents. In this study, we sought to demonstrate that alpha–2 adrenoceptors are present in Muller cells and that activation of ERKs is a direct result of alpha–2 adenroceptor activation. We also pharmacologically characterized the subtype of these Muller cell adrenoceptors. Method: Muller cells were isolated from Sprague–Dawley rats. ERK activity was evaluated by Western blot analysis as well as enzyme assays. 3H–Brimonidine radioligand binding assay to the Muller cell membrane was performed to demonstrate the presence of alpha–2 adrenoceptors in these cells. Displacement binding experiements with adrenoceptor subtype selective agents were used to pharmacologically characterize these receptors. Results: Specific saturable 3H–Brimonidine bindings are present in the Muller cells. These bindings can be displaced by selective alpha–2A adrenoceptor agonists as well as antagonists. Activation of ERKs in these cells correlated well with the efficacy of various alpha–2 adrenoceptor agonists and can be inhibited by adrenoceptor antagonists. Conclusions: Alpha–2 adrenoceptors are present in Muller cells and activation of ERKs is a direct activation of alpha–2 adenroceptor on these cells. These receptors appeared to be mainly the Alpha–2A adrenoceptor subtype.
Keywords: Muller cells • neuroprotection • retinal culture