Measurement of intracellular chloride activity in mouse liver slices with microelectrodes

Steady-state membrane potential (Vm) and intracellular Cl- activity (aCli) were measured with double-barreled Cl(-)-selective microelectrodes in mouse liver slices. In bathing solutions (33.8 degrees C) containing pyruvate, glutamate, fumarate, and glucose, Vm and aCli were -27.6 +/- 1.0 mV and 32.6 +/- 1.5 mM, respectively. This apparent value of aCli exceeded the level required for passive distribution of this ion (aCleq = 26.4 +/- 1.3 mM) by 6.2 +/- 1.0 mM. This difference was essentially unchanged in experiments where (i) Na+ was replaced by choline, (ii) HCO3- was removed, and (iii) Cl- was replaced by gluconate. These data argue against the presence of Na+- or HCO3(-)-coupled Cl- transport mechanisms in the plasma membrane of mouse liver cells. This implies that aCli is in fact at equilibrium and interference with the response of Cl(-)-selective microelectrodes by intracellular anions is responsible for the apparent difference between aCli and aCleq. We found that Cl(-)-selective microelectrodes containing Corning 477315 ligand are sensitive to taurocholate, a representative bile salt. Their selectivity to taurocholate is about 60-times their selectivity towards Cl-. This suggests that interference of bile acids at concentrations normally present in hepatocytes with determinations of aCli can account for the apparent difference aCli-aCleq.