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 journalArticle

15 Citations (Scopus)

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)
JournalAmerican Journal of Physiology - Gastrointestinal and Liver Physiology
Volume261
Issue number5 24-5
StatePublished - 1991

Fingerprint

Hepatocytes
Cell Membrane
Amiloride
4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid
Membranes
Membrane Potentials
Uncertainty

Keywords

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

ASJC Scopus subject areas

  • Physiology
  • Gastroenterology

Cite this

Plasma membrane H+-HCO3 - transport in rat hepatocytes : A principal role for Na+-coupled HCO3 - transport. / Fitz, J. G.; Lidofsky, S. D.; Xie, M. H.; Cochran, M.; Scharschmidt, B. F.

In: American Journal of Physiology - Gastrointestinal and Liver Physiology, Vol. 261, No. 5 24-5, 1991.

Research output: Contribution to journalArticle

@article{31b3dee90b3f456f912bb3cf08893e6f,
title = "Plasma membrane H+-HCO3 - transport in rat hepatocytes: A principal role for Na+-coupled HCO3 - transport",
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).",
keywords = "2',7'-bis(carboxyethyl)-5(6')-carboxyfluorescein, Membrane potential, pH, Sodium-hydrogen exchange",
author = "Fitz, {J. G.} and Lidofsky, {S. D.} and Xie, {M. H.} and M. Cochran and Scharschmidt, {B. F.}",
year = "1991",
language = "English (US)",
volume = "261",
journal = "American Journal of Physiology - Heart and Circulatory Physiology",
issn = "0363-6135",
publisher = "American Physiological Society",
number = "5 24-5",

}

TY - JOUR

T1 - Plasma membrane H+-HCO3 - transport in rat hepatocytes

T2 - A principal role for Na+-coupled HCO3 - transport

AU - Fitz, J. G.

AU - Lidofsky, S. D.

AU - Xie, M. H.

AU - Cochran, M.

AU - Scharschmidt, B. F.

PY - 1991

Y1 - 1991

N2 - 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).

AB - 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).

KW - 2',7'-bis(carboxyethyl)-5(6')-carboxyfluorescein

KW - Membrane potential

KW - pH

KW - Sodium-hydrogen exchange

UR - http://www.scopus.com/inward/record.url?scp=0026353338&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=0026353338&partnerID=8YFLogxK

M3 - Article

VL - 261

JO - American Journal of Physiology - Heart and Circulatory Physiology

JF - American Journal of Physiology - Heart and Circulatory Physiology

SN - 0363-6135

IS - 5 24-5

ER -