Low K+ increases Na(+)-K(+)-ATPase alpha- and beta-subunit mRNA and protein abundance in cultured renal proximal tubule cells.
Studies from this laboratory demonstrate that LLC-PK1/Cl4 cells, a cultured renal cell line, respond to incubation in low-K+ medium by coordinately increasing abundance of both alpha- and beta-subunits of Na(+)-K(+)-ATPase but increase only beta- and not alpha-mRNA levels (Lescale-Matys et al. J. Biol. Chem. 265: 17935-17940, 1990) and that alpha-abundance is likely increased as a result of increased efficiency of alpha-mRNA translation (L. Lescale-Matys and A. A. McDonough. J. Cell Biol. 111: 311A, 1990). The aim of this report was to determine if nontransformed kidney cells would respond to low K+ in a similar manner. We incubated primary cultures of rat proximal tubule cells in low K+ (0.25 mM) for up to 24 h to address this aim. Na(+)-K(+)-ATPase activity, measured enzymatically, and abundance of alpha- and beta-subunits, measured by immunoblot, were increased significantly and coordinately by 8 h of low K+, and, by 24 h of low K+, these parameters were increased to 2.17 +/- 0.34 (activity), 2.03 +/- 0.21 (alpha), and 2.39 +/- 0.48 (beta)-fold over control. Pretranslationally, beta-mRNA, measured by Northern blot analysis, increased to 1.76 +/- 0.35 after 3 h of low K+ and to 3.4 +/- 0.75-fold over control after 24 h of low K+. The increase in alpha-mRNA was smaller and delayed compared with the beta-mRNA response, but it was sufficient to account for the observed increase in alpha-protein and Na(+)-K(+)-ATPase activity at steady state: alpha-mRNA increased to 1.27 +/- 0.09 after 6 h and to 1.91 +/- 0.41-fold over control after 24 h in low K+. We conclude that the accumulation of sodium pumps in cultured renal proximal tubule cells, unlike LLC-PK1 cells, can be accounted for by increases in both alpha- and beta-subunit mRNA levels.
Tang
M J
MJ
Department of Physiology and Biophysics, University of Southern California School of Medicine, Los Angeles 90033.
McDonough
A A
AA
D000818:Animals; D015152:Blotting, Northern; D002478:Cells, Cultured; D015151:Immunoblotting; D007425:Intracellular Membranes / Q000378:metabolism; D007687:Kidney Tubules, Proximal / Q000166:cytology / Q000201:enzymology* / Q000378:metabolism; D009994:Osmolar Concentration; D011188:Potassium / Q000494:pharmacology*; D011506:Proteins / Q000378:metabolism; D012313:RNA / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D013997:Time Factors
D011506:Proteins; D012333:RNA, Messenger; D012313:RNA; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium