title: Amiloride added together with bumetanide completely blocks mouse 3T3-cell exit from G0/G1-phase and entry into S-phase.
abstract: In this study we tested the hypothesis that stimulation of univalent-cation fluxes which follow the addition of growth factors are required for cell transition through the G1-phase of the cell cycle. The effect of two drugs, amiloride and bumetanide, were tested on exit of BALB/c 3T3 cells from G0/G1-phase and entry into S-phase (DNA synthesis). Amiloride, an inhibitor of the Na+/H+ antiport, only partially inhibited DNA synthesis induced by serum. Bumetanide, an inhibitor of the Na+/K+ co-transport, only slightly suppressed DNA synthesis by itself, but when added together with amiloride completely blocked cell transition through G1 and entry into S-phase. Similar inhibitory effects of the two drugs were found on the induction of ornithine decarboxylase (ODC) (a marker of mid-G1-phase) in synchronized cells stimulated by either partially purified fibroblast growth factor (FGF) or serum. To test this hypothesis further, cells arrested in G0/G1 were stimulated by serum, insulin or FGF. All induced similar elevations of cellular K+ content during the early G1-phase of the cell cycle. However, serum and FGF, but not insulin, released the cells from the G0/G1 arrest, as measured by ODC enzyme induction. This result implies that the increase in cellular K+ content may be necessary but not sufficient for induction of early events during the G1-phase. The synergistic inhibitory effects of amiloride and bumetanide on the two activities stimulated by serum growth factors, namely ODC induction (mid-G1) and thymidine incorporation into DNA (S-phase), suggested that the amiloride-sensitive Na+/H+ antiport system together with the bumetanide-sensitive Na+/K+ transporter play a role in the mitogenic signal.
mesh_terms: D000584:Amiloride / Q000494:pharmacology*; D002034:Bumetanide / Q000494:pharmacology*; D002460:Cell Line; D004247:DNA / Q000096:biosynthesis; D004232:Diuretics / Q000494:pharmacology*; D004357:Drug Synergism; D005346:Fibroblast Growth Factors / Q000494:pharmacology; D007328:Insulin / Q000494:pharmacology; D007399:Interphase / Q000187:drug effects*; D009955:Ornithine Decarboxylase / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism; D012964:Sodium / Q000378:metabolism
chemical_list: D004232:Diuretics; D007328:Insulin; D002034:Bumetanide; D005346:Fibroblast Growth Factors; D000584:Amiloride; D004247:DNA; D012964:Sodium; D009955:Ornithine Decarboxylase; D011188:Potassium