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RL Gross, J Zhang, SM Wu; Adrenergic Modulation of Glutamate-Induced Calcium Signals in Dissociated Mouse Retinal Ganglion Cells . Invest. Ophthalmol. Vis. Sci. 2002;43(13):2205.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose:Glutamate-induced neurotoxic actions are thought to be associated with elevation of intracellular calcium. The objective of this project is to understand how adrenergic agents modulate glutamate-induced increase of intracellular calcium in mouse retinal ganglion cells and how they may protect ganglion cells from glutamate-induced damage. Methods:Enzymatically dissociated adult mouse (strain C57BL/6J) retinal ganglion cells were identified with monoclonal antibody against Thy1.2 and Cy3-conjugated secondary antibody. The dissociated neurons were loaded with Fura-2AM, and calcium signals were recorded with a cooled CCD camera attached to an inverted microscope. Results:In a previous study we have demonstrated that dissociated mouse ganglion cells can be identified by their Thy1.2 immuno-positive fluorescence. Application of glutamate increased the intracellular calcium level in retinal ganglion cells in a dose dependent manner. The EC50 for glutamate was 6.19µM (n=12). ß-adrenergic blockers, (s)(-)-propanolol, betaxolol and timolol compressed the dose-curve and shifted the EC50 to higher dose ranges, suggesting that they act as non-competitive blockers of the glutamate responses. The relative efficacy for inhibiting 20µM glutamate-induced calcium signals is (s)(-)-propanolol≷betaxolol≷≷timolol with average IC50 of 78.05µM, 235.7µM and 2167.05µM, respectively. The inhibitory actions persisted in the presence of H9, a PKA blocker and isopropanolol, a ß-receptor agonist, indicating that the down regulation of glutamate-induced calcium increase in mouse ganglion cells is possibly not mediated by activation of ß-adrenergic receptors or the PKA pathway. Conclusion:Glutamate-induced elevation of intracellular calcium in mouse retinal ganglion cells can be reversibly suppressed by ß-adrenergic blockers with relative efficacy of (s)(-)-propanolol ≷betaxolol ≷≷timolol. In addition to lowering intraocular pressure, ß-blockers may be potentially neuroprotective against ganglion cell damage induced by elevated glutamate levels in glaucomatous retinas.
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