Regulation of intracellular pH by electrogenic Na+/HCO3-co-transporters in embryonic neural stem cell-derived radial glia-like cells

A stroke causes a hypoxic brain microenvironment that alters neural cell metabolism resulting in cell membrane hyperpolarization and intracellular acidosis. We studied how intracellular pH (pH(i)) is regulated in differentiated mouse neural progenitor cells during hyperpolarizing conditions, induced by prompt reduction of the extra cellular K+ concentration. We found that the radial glia-like population in differentiating embryonic neural progenitor cells, but not neuronal cells, was rapidly acidified under these conditions. However, when extra cellular calcium was removed, an instant depolarization and recovery of the pH(i), back to normal levels, took place. The rapid recovery phase seen in the absence of calcium, was dependent on extracellular bicarbonate and could be inhibited by 50859, a potent Na/HCO3 cotransporter inhibitor. Immunostaining and PCR data, showed that NBCe1 (SLC4A4) and NBCn1 (SLC4A7) were expressed in the cell population and that the pH(i) recovery in the radial glial-like cells after calcium removal was mediated mainly by the electrogenic sodium bicarbonate transporter NBCe1 (SLC4A4). Our results indicate that extracellular calcium might hamper pH(i) regulation and Na/HCO3 cotransporter activity in a brain injury microenvironment. Our findings show that the NBC-type transporters are the main pH(i) regulating systems prevailing in glia-like progenitor cells and that these calcium sensitive transporters are important for neuronal progenitor cell proliferation, survival and neural stem cell differentiation.Peer reviewe

Tannic acid inhibits electrogenic Na+/HCO3- co-transporter activity in embryonic neural stem cell-derived radial glial-like cells

Self-renewing neural stem cells and progenitor cells are cell populations that generate radial glial cells and neurons through asymmetric division. Regulation of intracellular pH in stem cells with high metabolic activity is critical for both cell signaling and proliferation. We have recently found that a S0859-inhibitable electrogenic Na+/HCO3- co-transporter (NBCe1, Slc4a4), is the primary pH(i) regulatory mechanism in stem cell-derived radial glial-like cells. Here we show, by using the voltage-sensitive fluorescent dye DiBAC 4(3) and BCECF, a pH-sensitive dye, that an antioxidant, tannic acid (100 mu M), can inhibit potassium- and calcium-dependent rapid changes in membrane potential and NBCe1 mediated pH i regulation in brain-derived glial-like cells in vitro. Furthermore, neural stem cell differentiation and neurosphere formation (proliferation) were completely inhibited by tannic acid. The present study provides evidence that tannic acid is a natural inhibitor of NBCe1. It is tempting to speculate that tannic acid or related compounds that inhibits NBCe1-mediated pH(i) regulation in glial-like cells may also have bearing on the treatment of glial neoplasms. NeuroReport 31: 57-63 Copyright (c) 2019 The Author(s). Published by Wolters Kluwer Health, Inc.Peer reviewe