Na,K-ATPase expression and cell volume during hypertonic stress in human renal cells

Primary cultures of human renal cortex cells were incubated in hypertonic medium and low K+ medium to determine the effect on Na,K-ATPase alpha and beta subunit expression, cell water, and intracellular ions. Cells exhibited functional characteristics of proximal tubules based on PTH stimulation of cAMP and the presence of Na(+)-dependent phosphate transport. When either NaCl or sucrose was added to increase medium osmolality to 500 mOsm/kg, beta subunit mRNA increased relative to control between 2.4 and 3.2-fold by six hours, and was still near twofold higher after 24 hours, while alpha subunit mRNA increased to about 1.5 times control by six hours. In low K+ medium, only beta mRNA increased. Hypertonic incubation increased Na,K-ATPase activity by 39% to 66% after 24 hours. Cell water was 70% of control at one hour, but increased to 90% of control by 24 hours. Only about 40% of the volume regulatory increase depended on accumulation of Na+ and K+. These results demonstrate that primary cultures of human proximal tubule cells can respond to hypertonic stress by induction of Na,K-ATPase.