Regulation of hepatic Na(+)-HCO3- cotransport and pH by membrane potential difference.
Hepatocytes possess several mechanisms for membrane acid-base transport, which work in concert to maintain intracellular pH (pHi) in a narrow physiological range, despite metabolic processes that produce and consume substantial quantities of H+ and HCO3-.Na(+)-H+ and Cl(-)-HCO3- exchangers contribute to recovery from intracellular acidosis and alkalosis, respectively, but are largely inoperative at physiological values of pHi. Recent studies indicate that hepatocytes also possess a mechanism for coupled transport of Na+ and HCO3- across the basolateral membrane. This appears to be the dominant pathway for membrane acid-base transport operative under basal conditions, mediates influx of Na+ and HCO3-, and is an important contributor to recovery from intracellular acidosis. In this review, the properties of hepatic Na(+)-HCO3- cotransport are described with emphasis on its effects on pHi and Na+ homeostasis and on the possible role of membrane potential difference as a signal modulating the rate of HCO3- influx and pHi of hepatocytes through effects on this transporter.
Fitz
J G
JG
Duke University Medical Center, Durham, North Carolina 27710.
Lidofsky
S D
SD
Scharschmidt
B F
BF
D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D008099:Liver / Q000166:cytology / Q000378:metabolism* / Q000502:physiology; D008564:Membrane Potentials; D008954:Models, Biological; D027982:Sodium-Bicarbonate Symporters
D002352:Carrier Proteins; D027982:Sodium-Bicarbonate Symporters