Surplus Na+ pumps: how low-K(+)-incubated LLC-PK1 cells respond to K+ restoration.
We have previously shown that a pig kidney cell line (LLC-PK1/Cl4) responds to chronic exposure to 0.25 mM extracellular K+ by increasing the beta-, not alpha-, subunit mRNA levels and both alpha- and beta-abundance twofold over control. Our objective in the present study was to determine how the LLC-PK1/Cl4 cells respond when returned to control (5.5 mM) medium. A 1.8-fold increase in ouabain binding established that the induced pumps were expressed at the cell surface following 24-h incubation in low K+. On restoration to 5.5 mM K+, intracellular Na+ and K+ concentrations ([Na+]i and [K+]i, respectively) rapidly returned to control levels within 15 min. The doubled pool size of pumps in the chronic low K+ cells had no significant influence on the rate of ion restoration when compared with the rate in cells acutely exposed to low K+. Despite the rapid return of ions to control values, beta-mRNA levels remained elevated for 2 h, then sharply declined to control levels by 6 h of K+ restoration. From these data, we estimate that the half-life of beta-mRNA is 2-3 h during restoration. alpha-Subunit mRNA remained essentially unchanged from control after return of K+ to the medium and restoration of intracellular ions.(ABSTRACT TRUNCATED AT 250 WORDS)
Lescale-Matys
L
L
Department of Physiology and Biophysics, University of Southern California School of Medicine, Los Angeles 90033.
Putnam
D S
DS
McDonough
A A
AA
D000818:Animals; D001665:Binding Sites; D002460:Cell Line; D007425:Intracellular Membranes / Q000378:metabolism; D007477:Ions; D007668:Kidney / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism*; D009994:Osmolar Concentration; D010042:Ouabain / Q000378:metabolism; D011188:Potassium / Q000494:pharmacology*; D012333:RNA, Messenger / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000235:genetics / Q000378:metabolism*
D007477:Ions; D012333:RNA, Messenger; D010042:Ouabain; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium