Persistent effects of ouabain treatment on human lymphocytes: synthesis of DNA, RNA and protein in stimulated and unstimulated cells

Pretreatment of human lymphocytes for 2 days in 2 × 10−6 M ouabain caused irreversible loss of their subsequent capacity to stimulate in the mixed lymphocyte reaction (MLR). Pretreatment for the same period with 10−7 M ouabain resulted in an enhanced incorporation of thymidine into DNA of the responding cells in the MLR; this effect was also on the stimulating cells, as previously reported by Christen et al. (Cell. Immunol. 19, 137–142 (1975)). Pretreatment of stimulating lymphocytes with 10−7 M ouabain caused a persistent but reversible inhibition of the synthesis of RNA and protein in the MLR; peak incorporation of labelled uridine or alanine reached the same level as that of the control cultures, but 24 h later. Exactly the same persistent but reversible inhibition was found in the case of DNA synthesis of cells pretreated with 10−7 M ouabain and then stimulated by antigens (streptolysin-O and varidase) or by mitogens (phytohemagglutinin and concanavalin A); the same level of incorporation of labelled thymidine occurred but 24–48 h later than in the case of the controls. Pretreatment with the cardiotonic steroid under these conditions also resulted in a pronounced inhibition of the basal, unstimulated levels of RNA and protein synthesis in the case of both control lymphocytes and those which had been treated with mitomycin C. The effects of ouabain pretreatment on basal RNA and protein synthesis were identical for both 2 × 10−6 M and for 10−7 M; the effect of pretreatment of stimulating cells with these two concentrations was completely opposite: irreversible inhibition of the proliferative response of allogeneic responding cells at the former concentration and delayed activation at the latter.