Requirement of Cl- and Na+ for the ouabain-resistant control of cell volume in slices of rat liver.

The ability of liver cells to control their volume in the presence of ouabain has been studied in tissue slices that were recovering at 38 degrees C from a period of swelling at 1 degrees C. Morphological observations were made in conjunction with measurements of the net movement of water and ions. Extrusion of water in the presence of ouabain (2 mM) was accompanied by a net loss of Na+ and Cl- and by the formation of characteristic, rounded vesicles in the peri-canalicular regions of the hepatocytes; bile canaliculi were patent. When incubation was carried out in a medium in which either NO-3 or SO2-4 replaced Cl-, ouabain-resistant water extrusion was prevented and the cytoplasmic vesicles normally found with ouabain were almost totally absent. When these slices were subsequently transferred to Cl- medium with ouabain, extrusion of intracellular water was initiated and cytoplasmic vesicles reappeared. Replacement of medium Na+ by Li+ mimicked the effects of ouabain on water and ion movements and ultrastructure. In addition, the ouabain-resistant extrusion of water and Cl- was reduced and there was some diminution in the number of vesicles induced by ouabain. Furosemide (2 mM) had little effect on water movement or ultrastructure in the absence of ouabain, but it slowed the net water loss and substantially reduced the formation of cytoplasmic vesicles in the presence of ouabain. The results show a close relationship between ouabain-resistant water extrusion and the formation of the cytoplasmic vesicles that are characteristic of treatment with ouabain. They further suggest that a cotransport of Na+ and Cl- forms an important part of the mechanism underlying ouabain-resistant water extrusion and, specifically, that this cotransport may take place across the membranes of the cytoplasmic vesicles.