Increase in intracellular Na+: transmembrane signal for rejoining of DNA strand breaks in proliferating lymphocytes.
Two early events in the mitogen-induced entry of murine splenocytes into proliferation are (a) a rapid rise in influx of Na+, causing its total internal concentration to increase by 42 +/- 7% within 2 h of culture with concanavalin A (Con A), and (b) rejoining of some 3000 DNA strand breaks per diploid genome within the same period. Con A did not induce rejoining in low Na+ (less than 9 mM) medium, but the process began directly when Na+ was added, at its usual concentration, to the growth medium. Incubation of cells with ouabain, an inhibitor of the Na+K+-ATPase, or monensin, a Na+ ionophore, caused an increase in the internal Na+ concentration in normal, but not in low, Na+ medium. In the former (but not in the latter) medium, both ouabain and monensin caused rejoining of the DNA strand breaks to occur in resting lymphocytes, i.e., in the absence of mitogen. Stimulation of splenocytes with Con A also resulted in a rapid but transient increase in the level of intracellular free Ca2+. This effect was also observed in the absence of extracellular Na+; however, deprivation of extracellular Ca2+ completely abolished this effect. Moreover, the intracellular free Ca2+ level was significantly higher in cells suspended in Na+-free buffer or medium. Since the Con A-induced rejoining of DNA strand breaks occurred in the absence of extracellular Ca2+ and removal of extracellular Na+ had no inhibitory effect on the Con A-induced increase in the level of intracellular free Ca2+, the Con A-stimulated repair could not have been mediated by the initial increase in Ca2+ influx. The early mitogen-induced increase in the internal Na+ concentration is a necessary and sufficient signal for the rejoining of breaks, an event that must occur before the proliferating lymphocytes can replicate their DNA.
D000818:Animals; D002455:Cell Division; D003208:Concanavalin A / Q000494:pharmacology; D004260:DNA Repair; D008214:Lymphocytes / Q000166:cytology*; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D008985:Monensin / Q000494:pharmacology; D010042:Ouabain / Q000494:pharmacology; D012964:Sodium / Q000378:metabolism*; D013154:Spleen / Q000166:cytology / Q000187:drug effects
D003208:Concanavalin A; D010042:Ouabain; D008985:Monensin; D012964:Sodium