ROLE OF CHLORIDE-IONS IN LIVER-CELL VOLUME REGULATION

Hypotonic swelling of liver cells is followed by regulatory volume decrease (RVD), which has been shown to involve facilitated release of K+. In this study, the role of Cl- in RVD was examined by videoplanimetric analysis of cell volume and measurement of membrane potential (V(m)) and resistance (R(m)) in single isolated rat hepatocytes, and by measurement of Cl-36 efflux in the isolated perfused liver preloaded with the isotope. Liver cells subjected to hypotonic stress by removal of 50 mM external NaCl (70% of control osmolality) swelled from an initial volume of 6.68 +/- 0.77 to 8.27 +/- 0.88 pl (24.3 +/- 3.4% increase) within 1 min and exhibited RVD at an initial rate of 0.26 +/- 0.01 pl/min. A step decrease in external Cl- accelerated the initial rate of RVD to 0.53 +/- 0.08 pl/min. RVD was abolished in cells that had been depleted of Cl-. V(m) and R(m) displayed biphasic responses to hypotonic stress. An initial (< 15 s) hyperpolarization of V(m) from -35.4 +/- 2.2 to -38.8 +/- 2.6 mV was followed by a gradual depolarization reaching -30.2 +/- 2.0 mV by 1 min. In parallel, R(m) initially (< 15 s) increased from 101 +/- 13 to 121 +/- 17 M-OMEGA (19 +/- 3% increase) and then declined to 55 +/- 4 M-OMEGA (59 +/- 4% of initial R(m)) within 1 min. These changes were reversible upon return to isotonicity. By analysis of the dependence of V(m) on bath Cl- concentration, the partial membrane conductance to Cl- was determined and was found to increase from 2.26 +/- 0.36 nS in isotonic conditions to 5.85 +/- 0.79 nS 1 min after onset of hypotonic stress. Hypotonic stress also increased fractional release of Cl-36 in the isolated perfused liver from 16.6 +/- 1.5 to 26.7 +/- 3.2% liver content/min. These data show that hypotonic stress leads to an increase in cell membrane Cl- conductance that in turn facilitates RVD.