Electrogenic Na+/HCO3−cotransport in neuroglia

Abstract

Membrane potential recording from glial cells in Necturus optic nerve in the presence of 2 mM Ba⁺⁺, which was added to block the K⁺ conductance, gave the following results. (1) In HCO₃⁻-free, low-Na⁺ solutions (11% of control; Na⁺ replaced with N-methyl-D-glucamine), the hyperpolarizing effect of adding 10 mM HCO₃⁻ was reduced by approximately 80%.(2) 4-acetamido-4′-isothiocynato-stilbene-2,2′-disulfonic acid (SITS, 0.1 or 1 mM) reduced the effect of HCO₃⁻ by at least 50%.(3) In the presence of HCO₃⁻, reduction of Na⁺ caused a depolarization which was much larger than that observed in nominally HCO₃⁻-free solutions. These observations indicate the presence in the glial membrane of an electrogenic Na⁺/HCO₃⁻ contransporter in which the stoichiometry of HCO₃⁻ to Na⁺ is greater than 1.