REGULATION OF NA+-K+-ATPASE EXPRESSION IN CULTURED RENAL-CELLS BY INCUBATION IN HYPERTONIC MEDIUM

To determine whether alterations in cell volume affect Na+-K+-adenosinetriphosphatase (ATPase) expression, a subclone of the Madin-Darby canine kidney (MDCK) cell line was incubated in anisotonic serum-free medium and alpha- and beta-subunit mRNA, Na+-K+-ATPase activity, and active K+ transport were measured. In medium adjusted to 500 mosmol/kgH2O by adding NaCl, the alpha-subunit mRNA concentration was 2.93 +/- 0.14 (SE) times control and beta-mRNA was 1.93 +/- 0.27 times control. When sucrose was added to increase osmolality, alpha-subunit mRNA increased to 1.85 +/- 0.18 times control. Na+-K+-ATPase activity of homogenates from cells incubated in 500 mosmol/kgH2O medium for 24 h increased to 2.62 +/- 0.52 times control when NaCl was added and 2.31 +/- 0.34 times control when sucrose was added. Active K+ transport increased between 60 and 90% after cells were incubated in 450 mosmol/kgH2O medium with either NaCl or sucrose added. Stimulation of Na+-K+-ATPase expression in renal cells facing hypertonic stress may represent a long-term mechanism that allows cells to maintain cation gradients in a hypertonic environment.