Alanine uptake activates hepatocellular chloride channels

Cells involved in the retrieval and metabolic conversion of amino acids undergo significant increases in size in response to amino acid uptake. The resultant adaptive responses to cell swelling are thought to include increases in membrane K+ and Cl- permeability through activation of volume-sensitive ion channels. This viewpoint is largely based on experimental models of hypotonic swelling, but few mammalian cells experience hypotonic challenge in vivo. Here we have examined volume regulatory responses in a physiological model of cell-swelling alanine uptake in immortalized hepatocytes. Alanine-induced cell swelling was followed by a decrease in cell volume that was temporally associated with an increase in membrane Cl- currents. These currents were dependent both on alanine concentration and Na+, suggesting that currents were stimulated by Na+-coupled alanine uptake. Cl- currents were outwardly rectifying, exhibited an anion permeability sequence of I- > Br- > Cl-, and were inhibited by the Cl- channel blocker 5-nitro-2-(3-phenylpropylamino)benzoic acid, features similar to those reported for a widely distributed class of volume-sensitive anion channels evoked by experimental hypotonic stress. These findings suggest that volume-sensitive anion channels participate in adaptive responses to amino acid uptake and provide such channels with a new physiological context.