AJP - Gastrointestinal and Liver Physiology, Vol 261, Issue 3 512-G522, Copyright © 1991 by American Physiological Society

ARTICLES

Cl(-)-HCO3- exchanger in isolated rat hepatocytes: role in regulation of intracellular pH

A. Benedetti, M. Strazzabosco, J. G. Corasanti, P. Haddad, J. Graf and J. L. Boyer
Department of Medicine and Liver Center, Yale University School of Medicine, New Haven, Connecticut 06510.

In rat hepatocytes, basolateral Na(+)-H+ exchange and Na(+)-HCO3- cotransport function as acid extruders. To assess mechanisms of acid loading, intracellular pH (pHi) recovery from an alkaline load was analyzed in short-term cultured rat hepatocyte monolayers using the pH-sensitive dye BCECF. Electrophysiological techniques were also used to assess the role of the membrane potential (Vm). Cells were alkaline loaded by suddenly reducing external CO2 and HCO3- (from 10% and 50 mM, respectively, to 5% and 25 mM) at constant pHo. After this maneuver, pHi rapidly rose by 0.13 +/- 0.03 pH units (pHu) and recovered to baseline at an initial rate of 0.026 +/- 0.009 pHu/min. Intracellular buffering power was estimated from the dependence of pHi on [NH4+]o and varied between 70 and 10.5 mM/pHu in a pHi range of 6.5-7.6. Initial pHi recovery corresponded to a rate of OH- efflux (JOH) of 1.76 +/- 0.71 mM/min and was blocked by 0.5 mM DIDS (0.003 +/- 0.002; JOH = 0.18 +/- 0.06) or by 1 mM H2DIDS (0.001 +/- 0.002; JOH = 0.26 +/- 0.08) and by removal of [Cl-]o (0.003 +/- 0.007; JOH = 0.28 +/- 0.07). The dependence of JOH on [Cl-]o exhibited saturation kinetics with an apparent Km for [Cl-]o of 5.1 mM. pHi recovery was Na+ independent and was not inhibited by substitution of Na+ with NMDG (0.045 +/- 0.09; JOH = 2.94 +/- 0.59). During an alkaline load, cell Vm hyperpolarized from -33.4 +/- 1.8 to -43.4 +/- 2.8 mV, mainly due to an increase in K+ conductance by a factor of 2.8 +/- 0.3.(ABSTRACT TRUNCATED AT 250 WORDS)

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