Effects of mitogens on sodium-potassium transport, H-ouabain binding, and adenosine triphosphatase activity in lymphocytes

The effect of various mitogens was studied on sodium (Na⁺) potassium (K⁺) transport, ³H-ouabain binding, and adenosine triphosphatase (ATPase) activity in human and sheep peripheral lymphocytes. Concanavalin A (ConA), phytohemagglutinin (PHA), horse anti-lymphocyte serum (ALS), and anti-IgG antisera, in order of decreasing potency, stimulated in particular the ouabain-sensitive K⁺ pump influx, while the cardiac glycoside-insensitive K⁺ leak flux was only slightly affected. Sheep lymphocytes primed in vivo with human IgG as antigen also responded with K⁺ pump flux activation when exposed to the antigen in vitro. Both PHA and ConA also stimulated active Na⁺ efflux in human lymphocytes. Apparently these mitogens activate the Na⁺K⁺ pump system in the lymphocyte membrane—an assumption supported by the finding of a significant activation of the ouabain-sensitive Na⁺K⁺-ATPase. From rate studies of ³H-ouabain binding carried out at 37 °C in presence and absence of sodium azide, and at 0 °C, it is concluded that PHA alters the rate of ouabain uptake to these cells. Thus PHA may alter the affinity of the pump for ouabain, equivalent to an increased cation turnover per pump site. However, our findings do not completely discount the possibility that PHA also increases the total number of ouabain molecules bound and therefore of Na⁺K⁺ pumps.