Plasma membrane H+-HCO3- transport in rat hepatocytes: A principal role for Na+-coupled HCO3- transport

J. G. Fitz, S. D. Lidofsky, M. H. Xie, M. Cochran, B. F. Scharschmidt

Research output: Contribution to journalArticlepeer-review

15 Scopus citations

Abstract

Na+-coupled HCO3- transport has been demonstrated in the basolateral membrane of hepatocytes, but there is uncertainty regarding its stoichiometry or capacity compared with other mechanisms of H+-HCO3- transport. After preincubation in medium free of Na+, either in the presence or absence of HCO3--CO2, rat hepatocytes in primary culture were reexposed to Na+ or HCO3--CO2 alone or in combination. Transporter electrogenicity was assessed by measuring membrane potential difference (PD), and the relative capacities of Na+-coupled HCO3- transport, Cl--HCO3- exchange, and Na+-H+ exchange were assessed by measuring the magnitude and rate of change of intracellular pH (pH(i)) using BCECF. In the absence of Na+, exposure to HCO3- alone had no consistent effect on PD or pH(i). In the absence of HCO3-, reexposure to Na+ depolarized cells by 3 ± 1 mV and caused an amiloride-inhibitable increase in pH(i) of 0.031 ± 0.02 units/min. In the presence of HCO3-, reexposure to Na+ hyperpolarized cells by -14 ± 5 mV and increased pH(i) at a rate of 0.133 ± 0.11 units/min; both the hyperpolarization and alkalinization were inhibited by SITS but unaffected by amiloride. These changes in PD indicate that Na+-coupled HCO3- transport is electrogenic, consistent with coupling of more than one HCO3- to each Na+. Furthermore, SITS-inhibitable Na+-dependent alkalinization exceeds amiloride-inhibitable Na+-dependent alkalinization by an order of magnitude, suggesting that the transport capacity of Na+-coupled HCO3- transport exceeds that of Na+-H+ exchange. Because Na+-H+ exchange is inactive at physiological pH(i), Na+-coupled HCO3- transport may contribute importantly to membrane HCO3- flux and regulation of pH(i).

Original languageEnglish (US)
Pages (from-to)G803-G809
JournalAmerican Journal of Physiology - Gastrointestinal and Liver Physiology
Volume261
Issue number5 24-5
DOIs
StatePublished - 1991

Keywords

  • 2',7'-bis(carboxyethyl)-5(6')-carboxyfluorescein
  • Membrane potential
  • Sodium-hydrogen exchange
  • pH

ASJC Scopus subject areas

  • Physiology
  • Hepatology
  • Gastroenterology
  • Physiology (medical)

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