The role of anions in cellular volume regulation.

Cellular volume can be varied substantially by replacing medium Cl- isosmotically by other univalent anions. Since K+ content changes in parallel, cellular K+ concentration is well maintained. Gluconate behaves as an impermeant anion so cells shrink. Acetate enters cells apparently by non-ionic diffusion causing marked cellular swelling. These changes in volume are fully reversed when Cl- is again restored to the medium. However, ouabain (10(-3) M) largely prevents this reversal when Cl- replaces acetate, arguing against a ouabain-insensitive volume regulating mechanism. In toad urinary bladder, serosal gluconate inhibits transepithelial Na+ transport and cells shrink. Analysis suggests that cell shrinkage results in a loss of Ba2+-sensitive highly selective basolateral membrane K+ conductance channels.