Electrogenic Na + /HCO 3 − cotransport in neuroglia

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 HCO 3 − ‐free, low‐Na + solutions (11% of control; Na + replaced with N‐methyl‐D‐glucamine), the hyperpolarizing effect of adding 10 mM HCO 3 − 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 HCO 3 − by at least 50%.(3) In the presence of HCO 3 − , reduction of Na + caused a depolarization which was much larger than that observed in nominally HCO 3 − ‐free solutions. These observations indicate the presence in the glial membrane of an electrogenic Na + /HCO 3 − contransporter in which the stoichiometry of HCO 3 − to Na + is greater than 1.