The electrogenic sodium bicarbonate cotransporter NBCe1 is a high-affinity bicarbonate carrier in cortical astrocytes

Abstract

The electrogenic sodium bicarbonate cotransporter NBCe1 (SLC4A4) is a robust regulator of intracellular H+ and a significant base carrier in many cell types. Using wild-type (WT) and NBCe1-deficient (NBC-KO) mice, we have studied the role of NBCe1 in cortical astrocytes in culture and in situ by monitoring intracellular H+ using the H+-sensitive dye BCECF [2',7'-bis-(carboxyethyl)-5-(and-6)- carboxyfluorescein] in wide-field and confocal microscopy. Adding 0.1-3 mM HCO3- to an O2-gassed, HEPES-buffered saline solution lowered the intracellular H+ concentration with a Km of 0.65 mM HCO3- in WT astrocytes, but slowly raised [H+]i in NBCe1-KO astrocytes.HumanNBCe1 heterologously expressed in Xenopus oocytes could be activated by adding 1-3mMHCO3-, and even by residualHCO3- in a nominally CO2/HCO3--free saline solution. Our results demonstrate a surprisingly high apparent bicarbonate sensitivity mediated by NBCe1 in cortical astrocytes, suggesting that NBCe1 may operate over a wide bicarbonate concentration in these cells. © 2014 the authors.