title: Response of human lymphocytes to mitogen: at what stage is there a requirement for Ca2+?
abstract: In order for significant DNA synthesis to be observed in the case of human lymphocytes stimulated for 36 h in presence of phytohemagglutinin (PHA), Ca2+ must be present in the medium continuously for at least 20 h; access to Ca2+ for 10-h periods during the first 30 h was not sufficient to permit DNA synthesis to occur. Addition of the chelator EGTA from 0 to 60 h after stimulation caused severe inhibition of incorporation of labelled thymidine when this was measured after 36 to 144 h of culture. Equimolar calcium reversed the inhibition caused by EGTA. Incorporation of labelled uridine and leucine showed a temporal pattern of dependence on the presence of Ca2+ in the medium similar to that of thymidine. Ca2+ appears not to be required in the medium during the last half (i.e., 20-36 h) of the presynthetic G1 phase nor during S phase since removal of Ca2+ from the medium after 20 h did not prevent a subpopulation of lymphocytes from entering S phase 16 h later.
mesh_terms: D002118:Calcium / Q000494:pharmacology*; D004247:DNA / Q000096:biosynthesis; D004533:Egtazic Acid / Q000494:pharmacology; D006801:Humans; D007700:Kinetics; D037102:Lectins; D008213:Lymphocyte Activation; D008214:Lymphocytes / Q000187:drug effects / Q000378:metabolism*; D013936:Thymidine / Q000378:metabolism
chemical_list: D037102:Lectins; D004533:Egtazic Acid; D004247:DNA; D002118:Calcium; D013936:Thymidine