Release of taurine and glutamate contributes to cell volume regulation in human retinal Müller cells: differences in modulation by calcium

Neuronal activity in the retina generates osmotic gradients that lead to Muller cell swelling, followed by a regulatory volume decrease (RVD) response, partially due to the isoosmotic efflux of KCl and water. However, our previous studies in a human Muller cell line (MIO-M1) demonstrated that an important fraction of RVD may also involve the efflux of organic solutes. We also showed that RVD depends on the swelling-induced Ca2+ release from intracellular stores. Here we investigate the contribution of Taurine (Tau) and Glutamate (Glu), the most relevant amino acids in Muller cells, to RVD through the volume-regulated anion channel (VRAC), as well as their Ca2+-dependency in MIO-M1 cells. Swelling-induced [3-H]-Tau/[3H]-Glu release was assessed by radiotracer assays and cell volume by fluorescence videomicroscopy. Results showed that cells exhibited an osmosensitive efflux of [3H]-Tau and [3H]-Glu (Tau > Glu) blunted by the VRAC inhibitors DCPIB and CBX, reducing RVD. Only [3H]-Tau efflux was dependent on ...