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

Abstract

Effects of the Ca 2+-ionophore A23187 and concanavalin A on the membrane potential of human lymphocytes and rat thymocytes have been studied using the fluorescent potential probe diS-C 3-(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 Ca 2+, and on the type of lymphocytes, one of these effects predominates. The hyperpolarization induced by A23187 is caused by activation of Ca 2+-dependent K + channels. It is blocked by quinine and high concentrations of extracellular K +. The dependence of Ca 2+-activated K + transport on extracellular Ca 2+ 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 Ca 2+-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 Ca 2+ concentration and the increase in lymphocyte plasma membrane permeabilities to monovalent cations.