Cell Volume Regulation in Human Retinal Müller Cells is Associated with Changes in Transmembrane Potential.

JUAN MANUEL FERNÁNDEZ; GISELA DI GIUSTO; MAIA KALSTEIN; LUCIANA MELAMUD; VALERIA RIVAROLA; PAULA FORD; CLAUDIA CAPURRO

PLOS ONE

PUBLIC LIBRARY SCIENCE

Lugar: San Francisco; Año: 2013 vol. 8 p. 1 - 11

1932-6203

Mu¨ ller cells are mainly involved in controlling extracellular homeostasis in the retina, where intense neural activity alters ion concentrations and osmotic gradients, thus favoring cell swelling. This increase in cell volume is followed by a regulatory volume decrease response (RVD), which is known to be partially mediated by the activation of K+ and anion channels. However, the precise mechanisms underlying osmotic swelling and subsequent cell volume regulation in Mu¨ ller cells have been evaluated by only a few studies. Although the activation of ion channels during the RVD response may alter transmembrane potential (Vm), no studies have actually addressed this issue in Mu¨ ller cells. The aim of the present work is to evaluate RVD using a retinal Mu¨ ller cell line (MIO-M1) under different extracellular ionic conditions, and to study a possible association between RVD and changes in Vm. Cell volume and Vm changes were evaluated using fluorescent probe techniques and a mathematical model. Results show that cell swelling and subsequent RVD were accompanied by Vm depolarization followed by repolarization. This response depended on the composition of extracellular media. Cells exposed to a hypoosmotic solution with reduced ionic strength underwent maximum RVD and had a larger repolarization. Both of these responses were reduced by K+ or Cl2 channel blockers. In contrast, cells facing a hypoosmotic solution with the same ionic strength as the isoosmotic solution showed a lower RVD and a smaller repolarization and were not affected by blockers. Together, experimental and simulated data led us to propose that the efficiency of the RVD process in Mu¨ ller glia depends not only on the activation of ion channels, but is also strongly modulated by concurrent changes in the membrane potential. The relationship between ionic fluxes, changes in ion permeabilities and ion concentrations ?all leading to changes in Vm? define the success of RVD.