REDISTRIBUTION OF HEPATOCYTE CHLORIDE DURING L-ALANINE UPTAKE

We used ion-sensitive, double-barrel microelectrodes to measure change s in hepatocyte transmembrane potential (V(m)), intracellular K+, Cl-, and Na+ activities (a(K)i, a(Cl)i and a(Na)i), and water volume durin g L-alanine uptake. Mouse liver slices were superfused with control an d experimental Krebs physiological salt solutions. The experimental so lution contained 20 mM L-alanine, and the control solution was adjuste d to the same osmolality (305 mOsm) with added sucrose. Hepatocytes al so were loaded with 50 mM tetramethylammonium ion (TMA+) for 10 min. C hanges in cell water volume during L-alanine uptake were determined by changes in intracellular, steady-state TMA+ activity measured with th e K+ electrode. Hepatocyte control V(m) was -33 +/- 1 mV. L-alanine up take first depolarized V(m) by 2 +/- 0.2 mV and then hyperpolarized V( m) by 5 mV to -38 +/- 1 mV (n = 16) over 6 to 13 min. During this hype rpolarization, a(Na)i increased by 30% from 19 +/- 2 to 25 +/- 3 mM (P < 0.01), and a(K)i did not change significantly from 83 +/- 3 mM. How ever, with added ouabain (1 mM) L-alanine caused only a 2-mV increase in V(m), but now a(K)i decreased from 61 +/- 3 to 54 +/- 5 mM (P < 0.0 5). Hyperpolarization of V(m) by L-alanine uptake also resulted in a 3 8% decrease of a(Cl)i from 20 +/- 2 to 12 +/- 3 mM (P < 0.001). Change s in V(m) and V(Cl) - V(m) voltage traces were parallel during the tim e Of L-alanine hyperpolarization, which is consistent with passive dis tribution of intracellular Cl- with the V(m) in hepatocytes. Added Ba2 + abolished the L-alanine-induced hyperpolarization, and a(Cl)i remain ed unchanged. Hepatocyte water volume during L-alanine uptake increase d by 12 +/- 3%. This swelling did not account for any changes in ion a ctivities following L-alanine uptake. We conclude that hepatocyte a(K) i is regulated by increased Na+-K+ pump activity during L-alanine upta ke in spite of cell swelling and increased V(m) due to increased K+ co nductance. The hyperpolarization of V(m) during L-alanine uptake provi des electromotive force to decrease a(Cl)i. The latter may contribute to hepatocyte volume regulation during organic solute transport.