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.
D000818:Animals; D000001:Calcimycin / Q000494:pharmacology*; D002118:Calcium / Q000494:pharmacology; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology; D003208:Concanavalin A / Q000494:pharmacology*; D004533:Egtazic Acid / Q000494:pharmacology; D006801:Humans; D007700:Kinetics; D008214:Lymphocytes / Q000187:drug effects / Q000502:physiology*; D008564:Membrane Potentials / Q000187:drug effects; D051381:Rats; D011919:Rats, Inbred Strains; D013050:Spectrometry, Fluorescence; D013601:T-Lymphocytes / Q000502:physiology; D013950:Thymus Gland / Q000502:physiology*
D003208:Concanavalin A; D000001:Calcimycin; D004533:Egtazic Acid; D002118:Calcium