Electrophysiological evidence for Na+-coupled bicarbonate transport in cultured rat hepatocytes

J. G. Fitz, M. Persico, B. F. Scharschmidt

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Abstract

Recent observations suggest that hepatocytes exhibit basolateral electrogenic Na+-coupled HCO3 - transport. In these studies, we have further investigated this transport mechanism in primary culture of rat hepatocytes using intracellular microelectrodes to measure membrane potential difference (PD) and the pH-sensitive fluorochrome 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein to measure intracellular pH (pH(i)). In balanced media containing 25 mM HCO3 -, PD averaged -32.1 ± 0.6 (SE) mV and pH(i) averaged 7.22 ± 0.03. PD became more negative (hyperpolarized) when extracellular [HCO3 -] was increased and less negative (depolarized) when extracellular HCO3 - was decreased. Acute replacement of extracellular Na+ by choline also resulted in membrane depolarization of 18.0 ± 1.6 mV, suggesting net transfer of negative charge. This decrease in PD upon Na+ removal was HCO3 --dependent, amiloride insensitive, and inhibited by the disulfonic stilbene 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid (SITS). PD also decreased upon acute exposure to SITS. The degree of depolarization seen with removal of Na+ or HCO3 - correlated directly with resting PD (r = 0.81 and 0.95, respectively), suggesting a voltage-dependent mechanism. Removal of extracellular Na+ also decreased pH(i) to 7.06 ± 0.02, and this acidification was decreased in the absence of HCO3 - or in the presence of SITS or amiloride. These studies provide direct evidence for electrogenic Na+-coupled HCO3 - transport in rat hepatocytes. Further, they suggest that it represents a major pathway for conductive movement of Na+ across the membrane and that it contributes, along with Na+-H+ exchange, to the intracellular acidification observed upon removal of extracellular Na+. Thermodynamic considerations as well as the acute effect of SITS on PD suggest that this mechanism may mediate influx of Na+, HCO3 -, and net negative charge under basal conditions and that it may be regulated in part by the membrane PD.

Original languageEnglish (US)
JournalAmerican Journal of Physiology - Gastrointestinal and Liver Physiology
Volume256
Issue number3
StatePublished - 1989

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4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid
Bicarbonates
Hepatocytes
Membrane Potentials
Amiloride
Stilbenes
Membranes
Microelectrodes
Choline
Fluorescent Dyes
Thermodynamics
Acids

ASJC Scopus subject areas

  • Physiology
  • Gastroenterology

Cite this

Electrophysiological evidence for Na+-coupled bicarbonate transport in cultured rat hepatocytes. / Fitz, J. G.; Persico, M.; Scharschmidt, B. F.

In: American Journal of Physiology - Gastrointestinal and Liver Physiology, Vol. 256, No. 3, 1989.

Research output: Contribution to journalArticle

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