HCO3--coupled Na+ influx is a major determinant of Na+ turnover and Na+/K+ pump activity in rat hepatocytes

J. Gregory Fitz, Steven D. Lidofsky, Richard A. Weisiger, Ming Hong Xie, Mary Cochran, Thomas Grotmol, Bruce F. Scharschmidt

Research output: Contribution to journalArticle

15 Scopus citations

Abstract

Recent studies in hepatocytes indicate that Na+-coupled HCO3- transport contributes importantly, to regulation of intracellular pH and membrane HCO3- transport. However, the direction of net coupled Na+ and HCO3- movement and the effect of HCO3- on Na+ turnover and Na+/K+ pump activity are not known. In these studies, the effect of HCO3- on Na+ influx and turnover were measured in primary rat hepatocyte cultures with22Na+, and [Na+]i was measured in single hepatocytes using the Na+-sensitive fluorochrome SBFI. Na+/K+ pump activity was measured in intact perfused rat liver and hepatocyte monolayers as Na+-dependent or ouabain-suppressible86Rb uptake, and was measured in single hepatocytes as the effect of transient pump inhibition by removal of extracellular K+ on membrane potential difference (PD) and [Na+]i. In hepatocyte monolayers, HCO3- increased22Na+ entry and turnover rates by 50-65%, without measurably altering22Na+ pool size or cell volume, and HCO3- also increased Na+/K+ pump activity by 70%. In single cells, exposure to HCO3- produced an abrupt and sustained rise in [Na+]i, from ≈8 to 12 mm. Na+/K+ pump activity assessed in single cells by PD excursions during transient K+ removal increased ≃2.5-fold in the presence of HCO3-, and the rise in [Na+]i produced by inhibition of the Na+/K+ pump was similarly increased ≃2.5-fold in the presence of HCO3-. In intact perfused rat liver, HCO3- increased both Na+/K+ pump activity and O2 consumption. These findings indicate that, in hepatocytes, net coupled Na+ and HCO3- movement is inward and represents a major determinant of Na+ influx and Na+/K+ pump activity. About half of hepatic Na+/K+ pump activity appears dedicated to recycling Na+ entering in conjunction with HCO3- to maintain [Na+]i within the physiologic range.

Original languageEnglish (US)
Pages (from-to)1-10
Number of pages10
JournalThe Journal of Membrane Biology
Volume122
Issue number1
DOIs
StatePublished - May 1991

Keywords

  • Na/HCO cotransport
  • SBFI
  • ion transport
  • membrane potential
  • microelectrodes
  • symport

ASJC Scopus subject areas

  • Biophysics
  • Physiology
  • Cell Biology

Fingerprint Dive into the research topics of 'HCO<sub>3</sub><sup>-</sup>-coupled Na<sup>+</sup> influx is a major determinant of Na<sup>+</sup> turnover and Na<sup>+</sup>/K<sup>+</sup> pump activity in rat hepatocytes'. Together they form a unique fingerprint.

Cite this