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

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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

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Hepatocytes
Liver
Intracellular Membranes
Recycling
Ouabain
Fluorescent Dyes
Cell Size
Membrane Potentials

Keywords

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

ASJC Scopus subject areas

  • Physiology
  • Cell Biology
  • Biophysics

Cite this

HCO3 --coupled Na+ influx is a major determinant of Na+ turnover and Na+/K+ pump activity in rat hepatocytes. / Fitz, J. Gregory; Lidofsky, Steven D.; Weisiger, Richard A.; Xie, Ming Hong; Cochran, Mary; Grotmol, Thomas; Scharschmidt, Bruce F.

In: The Journal of Membrane Biology, Vol. 122, No. 1, 05.1991, p. 1-10.

Research output: Contribution to journalArticle

Fitz, J. Gregory ; Lidofsky, Steven D. ; Weisiger, Richard A. ; Xie, Ming Hong ; Cochran, Mary ; Grotmol, Thomas ; Scharschmidt, Bruce F. / HCO3 --coupled Na+ influx is a major determinant of Na+ turnover and Na+/K+ pump activity in rat hepatocytes. In: The Journal of Membrane Biology. 1991 ; Vol. 122, No. 1. pp. 1-10.
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T1 - HCO3 --coupled Na+ influx is a major determinant of Na+ turnover and Na+/K+ pump activity in rat hepatocytes

AU - Fitz, J. Gregory

AU - Lidofsky, Steven D.

AU - Weisiger, Richard A.

AU - Xie, Ming Hong

AU - Cochran, Mary

AU - Grotmol, Thomas

AU - Scharschmidt, Bruce F.

PY - 1991/5

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N2 - 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.

AB - 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.

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KW - membrane potential

KW - microelectrodes

KW - Na/HCO cotransport

KW - SBFI

KW - symport

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