The effects of ionophore A23187 and concanavalin A on the membrane potential of human peripheral blood lymphocytes and rat thymocytes.

Effects of the Ca2+-ionophore A23187 and concanavalin A on the membrane potential of human lymphocytes and rat thymocytes have been studied using the fluorescent potential probe diS-C3-(5). At concentrations of 10(-8) to 10(-6) M A23187 changes the membrane potential, inducing both hyper- and depolarization. Depending on concentrations of A23187 and the external Ca2+, and on the type of lymphocytes, one of these effects predominates. The hyperpolarization induced by A23187 is caused by activation of Ca2+-dependent K+ channels. It is blocked by quinine and high concentrations of extracellular K+. The dependence of Ca2+-activated K+ transport on extracellular Ca2+ and its sensitivity to calmodulin antagonists is different for human lymphocytes and for thymocytes. As distinct from lymphocytes, in thymocytes calmodulin is not involved in activation of Ca2+-dependent K+ transport. The depolarization induced in lymphocytes by A23187 is caused by an increase in Na+ permeability of the lymphocyte plasma membrane: it is eliminated in a low-Na+ medium. At mitogenic concentrations concanavalin A does not change the membrane potential of the lymphocytes. The results obtained permit elucidation of the relationship between two early events in lymphocyte activation, namely the increase in intracellular Ca2+ concentration and the increase in lymphocyte plasma membrane permeabilities to monovalent cations.