Ion contents of human lymphocytes: The effects of concanavalin A and ouabain

It has been suggested that mitogens may activate the Na,K-ATPase to cause an increased cell K + which may then trigger metabolic events initiating DNA synthesis. To test this hypothesis, human lymphocytes were treated with ouabain and concanavalin A (ConA) and their ion contents measured directly by atomic absorption. Ouabain decreased cell K + with a critical dose range, 10 −8 to 10 −7 M, similar to that which inhibits mitogenesis, and induced a mole-for-mole replacement of K + by Na +. ConA, in non-toxic, mitogenic doses, also caused a rapid and a sustained decrease in cell K +, but, unlike ouabain, did not induce replacement of the lost K + by Na +, and the total K + + Na + was reduced in spite of a normal water content. Thus, although normal Na,K-ATPase function may be required for mitogenesis, ConA does not affect cell K + and Na + simply by activating the Na,K-ATPase. Stable-state K + and Na + contents were then determined over a wide range of external K + levels, and analyzed by the equivalent of a Hill plot. The normal cooperative uptake of K + was inhibited in an allosteric manner by ouabain, while ConA failed to alter significantly the critical parameters of K +-Na + exchange and the cooperativity in K + uptake. We suggest that K + is not a specific trigger in the initiation of mitogenesis, but that changes in K + flux and content reflect a change within the physical state of an underlying macromolecular assembly that is poised to respond to the mitogenic stimulus in a critical cooperative fashion.