Early glial cell reactivity in experimental retinal detachment: effect of suramin

PURPOSE: In a rabbit model of retinal detachment, early Müller glial cell reactivity was monitored-specifically, changes in membrane features-to determine whether these changes involve an upregulation of purinergic P2 receptor-mediated responses and whether all or some of these alterations could be blocked by suramin or pyridoxal phosphate 6-azophenyl-2',4'-disulfonic acid (PPADS). In addition, the immune cell reactivity (microglial cells and blood-derived immune cells) was monitored. METHODS: A local retinal detachment was induced by subretinal injection of a sodium hyaluronate solution. Three, 24, 48, and 72 hours after surgery, Müller cells were acutely isolated, and patch-clamp records of the whole-cell potassium currents were made. The presence of P2 receptor-mediated responses was determined by measuring extracellular adenosine triphosphate (ATP)-induced membrane current increases, and by recording of ATP-induced calcium responses at the vitreal surface of retinal wholemounts. The density of isolectin B(4)-labeled immune cells was determined in the nerve fiber layer of retinal wholemounts. RESULTS: Within 24 hours of detachment, Müller cell reactivity was evident. The cells downregulated the density of their inwardly rectifying potassium currents to 60% and 47% of the control value at 48 hours and 72 hours of detachment, respectively. This downregulation was accompanied by an enhanced incidence of cells which showed calcium and current responses after ATP application (control: 14%; 24 hours of detachment: 42%; 72 hours of detachment: 80%). Müller cell hypertrophy was apparent at 48 and 72 hours of detachment. Application of suramin during surgery inhibited the downregulation of potassium currents, but not the elevated responsiveness to extracellular ATP; PPADS had no effect. Suramin also inhibited the inflammatory response that was induced by the surgical procedure and that was apparent by the increased number of immune cells. CONCLUSIONS: Reactive responses of Müller cells occur within 24 hours of detachment. Suramin inhibits several (but not all) reactive glial alterations and therefore may represent one candidate for further investigations in the search for drugs that limit detrimental effects of immune cell activation and Müller cell gliosis during retinal detachment.