Intracellular free magnesium in human lymphocytes and the response to lectins.

1. Intracellular free Mg2+] was measured in human peripheral blood lymphocytes using a fluorimetric method based on the dye furaptra. It was necessary to correct for the extracellular leakage of the dye by using either 10 mmol/l EDTA or 0.05 mmol/l Mn2+. 2. As the proliferative response of lymphocytes to mitogenic lectins has been linked to a dependence on extracellular Mg2+, the intracellular Mg2+] was studied in lymphocytes stimulated with various mitogenic and non-mitogenic lectins. 3. Only lymphocytes treated with phytohaemagglutinin-L, a leucoagglutinin from Phaseolus vulgaris that binds to tri- and tetra-antennary complex glycoproteins, showed a marked increase in intracellular Mg2+]. This effect was partially inhibited by N-acetylgalactosamine. The stimulation by different lectins of the incorporation of 3H]-thymidine into lymphocytes was not correlated to the changes in intracellular Mg2+]. 4. The proliferative response of lymphocytes to lectins is therefore not wholly dependent on a rise in intracellular Mg2+].