Regulation of Cell Volume in a Human Biliary Cell Line: Activation of K+ and Cl- Currents

The mechanisms responsible for recovery from cell swelling were evaluated in Mz-ChA-1 cells from human cholangiocarcinoma, a model biliary cell line. Exposure to hypotonic buffer (40% less NaCl) rapidly increased relative cell volume to 1.35 +/- 0.10 as measured by a Coulter Multisizer, followed by regulatory volume decrease to 1.08 +/- 0.03 by 30 min. The same maneuver increased 86Rb (69 +/- 17%) and 125I (422 +/- 58%) efflux in cell monolayers. 86Rb efflux was selectively inhibited by Ba2+ [half-maximal inhibitory concentration (IC50) approximately 1.5 mM], and 125I by 5-nitro-2-(3-phenylpropylamino)-benzoic acid (NPPB) (IC60 approximately 50 microM). Inhibition of these conductive pathways partially inhibited recovery from swelling. Membrane conductance measured by whole cell patch-clamp analysis increased in 57 of 57 cells during swelling due to activation of both K+ and Cl- conductances in most cells. K+ currents (75% of cells, 881 +/- 150 pA at 0 mV) were nearly linear and Ba2+ sensitive; Cl- currents (70% of cells, 2,696 +/- 244 pA at +60 mV) were outwardly rectified, showed time-dependent inactivation at depolarizing potentials, and were inhibited by NPPB. Chelation of cytosolic Ca2+ decreased swelling-induced isotope efflux, prevented activation of macroscopic K+ and Cl- currents, and blocked volume recovery. These studies indicate that biliary cells are able to regulate cell volume during osmotic stress by activation of separate K+ and Cl- conductances through a mechanism that depends in part on Ca(2+)-sensitive signaling pathways.