Epithelial cell volume regulation in hypotonic fluids: studies using a model tissue culture renal epithelial cell system.

The cultured renal epithelial cell line MDCK has been used in a study of cell volume regulation, emphasis being placed upon cell swelling in hypotonic media. MDCK cell volume was measured directly by electronic cell sizing using a Coulter counter in MDCK cell suspensions; this method gave comparable values for cell water when compared with those obtained using an intracellular space marker [14C]3-O-methyl glucose. MDCK cells behaved as perfect osmometers when suspended in hypertonic fluid (cell shrinkage). Cellular swelling in hypotonic media, in certain conditions, was found to be less than expected for an ideal osmometer. Non-ideal swelling was found to be the result of a substantial loss of intracellular K+ (Cl-) due to a specific increase in membrane K+ permeability. The membrane channel mediating the increased net K+ loss was separate, by pharmacological identity, from the Na+-K+ pump, the diuretic-sensitive co-transport system and a Gardos-type channel inhibited by quinine. A role for increased Ca2+ influx mediating the increased K+ permeability is suggested by results from hypotonic exposure in nominally Ca2+-free solutions.