Osmosensitive Release of Taurine And Glutamate Participate In Cell Volume Regulation In Retinal Müller Cells

HERMINIA PASANTES-MORALES; VANINA NETTI; CAPURRO CLAUDIA; ALEJANDRO PIZZONI; GERARDO RAMOS-MANDUJANO; MARTHA PÉREZ-DOMÍNGUEZ

Congreso; 38th World Congress of the International Union of Physiological Sciences; 2017

Müller cells are involved in controlling extracellular homeostasis in the retina, where neural activity altersosmotic gradients, favoring cell swelling. This swelling is followed by a regulatory volume decrease (RVD)mediated by an efflux of osmolytes and water transport by Aquaporin-4 (AQP4). We previouslydemonstrated in a human Müller cells (MIO-M1) that RVD partially depends on an efflux of KCl, but animportant fraction of this response may depend on the release of other solutes, such as Taurine (Tau) andGlutamate (Glu), poorly studied in Müller cells. Thus, the aim of this study was to evaluate the contributionof Tau and Glu efflux to RVD and to identify the involved signaling pathways in MIO-M1 cells. Cell volumewas evaluated by FURA-2 AM fluorescence and [3H]-Tau/[3H]-Glu release was assessed by measuringradioactivity in culture supernatant after the hypotonic shock (ΔOsm:100 mOsm). Results showed that MIOM1cells exposed to hypotonicity exhibited an efflux of [3H]-Tau and [3H]-Glu which was prevented by thevolume-regulated anion channel (VRAC) blocker DCPIB, reducing RVD by 60%. During hypotonicity,[3H]-Tau efflux was decreased in Ca2+-free medium and even further reduced by the intracellular Ca2+chelator BAPTA-AM, whereas [3H]-Glu release was insensitive to both conditions. RVD was unaffected inCa2+-free medium but it was lowered by 50% in the presence of BAPTA-AM. PI3K inhibition withWortmannin reduced both [3H]-Tau and [3H]-Glu efflux by 47 and 75%, respectively, decreasing RVD. Onthe other hand, PKC inhibition with Gö6976 did not affect [3H]-Tau and [3H]-Glu efflux, but RVD andosmotic water permeability were increased by 75% and 25%, respectively. These results suggest that Tau andGlu released by VRAC have a relevant role in RVD in MIO-M1 cells. PI3K activation represents a majorregulatory mechanism for both osmolytes efflux, but only Tau release was influenced by Ca2+. Ca2+-independent Glu efflux may support RVD in Ca2+-free medium, but it may not be sufficient when Ca2+release from intracellular stores is impaired. PKC is not directly involved in modulating osmolytes efflux,but it may affect water permeability mediated by AQP4, decreasing the RVD response. These findingssupport a role of Tau and Glu as osmolytes for RVD in Müller cells, key regulators of the retinalmicroenvironment.