K(+)-induced alkalinization in mouse cerebral astrocytes mediated by reversal of electrogenic Na(+)-HCO3- cotransport.
Raising extracellular K+ concentration ([K+]o) induces an alkaline shift of intracellular pH (pHi) in astrocytes. The mechanism of this effect was examined using the fluorescent pHi indicator 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein in primary cultures of mouse cerebral astrocytes. Raising [K+]o from 3 to 12 mM increased pHi by 0.28 pH units in 26 mM HCO(3-)-buffered solution. In nominally HCO(3-)-free solution (containing approximately 95 microM HCO3-), the alkalinization fell to 0.21 pH units and further to 0.08 pH units on removal of atmospheric CO2, suggesting a process with high affinity for HCO3-. This effect was Na+ dependent, Cl- independent, and inhibited by 0.5 mM 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid, indicating the involvement of Na(+)-HCO3- cotransport. The relationship between pHi and log[K+]o was found to be linear and to predict a stoichiometry of at least two HCO3- transported with each Na+. After removal of exogenous CO2/HCO3-, the direction of changes in pHi elicited by adding 1 mM HCO3- showed that net flux of HCO3- via the Na(+)-HCO3- cotransporter was outward at rest and was reversed by depolarization.
Brookes
N
N
Department of Pharmacology and Experimental Therapeutics, University of Maryland School of Medicine, Baltimore 21201.
Turner
R J
RJ
D000818:Animals; D001253:Astrocytes / Q000378:metabolism*; D001639:Bicarbonates / Q000378:metabolism*; D001921:Brain / Q000378:metabolism; D002352:Carrier Proteins / Q000502:physiology*; D002478:Cells, Cultured; D006863:Hydrogen-Ion Concentration; D051379:Mice; D011188:Potassium / Q000494:pharmacology*; D027982:Sodium-Bicarbonate Symporters; D017923:Sodium-Hydrogen Exchangers / Q000502:physiology
D001639:Bicarbonates; D002352:Carrier Proteins; D027982:Sodium-Bicarbonate Symporters; D017923:Sodium-Hydrogen Exchangers; D011188:Potassium