title: Stimulation by serum of the Na+/H+ antiporter in quiescent pig kidney epithelial (LLC-PK1) cells and role of the antiporter in the reinitiation of DNA synthesis.
abstract: LLC-PK1 cells can be brought into a classical quiescent state by depriving them of serum for 6 days. At this time, pulse-labeling with [3H]-thymidine shows that only 3% of the cells are synthesizing DNA, but the quiescent cells can be stimulated with serum to re-enter the cell cycle at a point early in G1. The rate of amiloride-sensitive 22Na+ uptake (as a measure of the Na+/H+ antiporter) is relatively low during quiescence; it rises 2- to 3-fold within 4 h after serum addition. This increase in antiporter activity appears to be required for the resumption of DNA synthesis in the absence of bicarbonate, because ethylisopropylamiloride (EIPA) blocks [3H]-thymidine incorporation when serum is added to cells in bicarbonate-free medium. In the presence of bicarbonate, however, EIPA has no effect on [3H]-thymidine incorporation, indicating that another (bicarbonate-dependent) transport system can substitute for the antiporter under these conditions.
mesh_terms: D000584:Amiloride / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D001769:Blood; D002352:Carrier Proteins / Q000378:metabolism*; D004261:DNA Replication / Q000187:drug effects*; D006863:Hydrogen-Ion Concentration; D007668:Kidney / Q000378:metabolism*; D017923:Sodium-Hydrogen Exchangers; D013552:Swine; D013936:Thymidine / Q000378:metabolism
chemical_list: D002352:Carrier Proteins; D017923:Sodium-Hydrogen Exchangers; C039465:5-dimethylamiloride; D000584:Amiloride; D013936:Thymidine