The relationship between mitogen-induced membrane potential changes and intracellular free calcium in human T-lymphocytes.
We have investigated the effects of mitogenic lectins on human T-lymphocytes, isolated from peripheral blood, and cells from the T-cell clone, HPB-ALL, using the fluorescent dyes, bis-thiobarbiturate tri-methineoxonol (bisoxonol) and quin2 to sense changes in membrane potential and intracellular free [Ca2+], respectively. The resting potential of both cell types is close to the K+ equilibrium potential. Changes from the resting level occur when mitogenic concentrations of either concanavalin A or phytohaemagglutinin are added. T-lymphocytes undergo a decrease in emission, maximal at 1 to 2 min, corresponding to a small membrane hyperpolarization. This is followed by a depolarization to approximately the resting level. HPB-ALL cells, on the other hand, respond to the mitogens by a sustained increase in fluorescence, denoting a depolarization, that is maximal at 4 to 5 min and 7 to 9 min, respectively. The Ca2+-dependence of these phenomena indicates that the membrane potential response, in both cell types, is the resultant of two opposing effects: a Ca2+-sensitive ion movement tending to hyperpolarize the cells and a Ca2+-insensitive effect that generates a depolarization. Our results suggest that Ca2+-activated K+ channels are responsible for the first effect and that an inward Na+ movement accounts for the depolarization signal in T-lymphocytes. In HPB-ALL cells only part of the depolarization is Na+-dependent. Although the effects elicited by phytohaemagglutinin occur more slowly than those produced by concanavalin A, similar membrane potential and [Ca2+]i changes occur.
D000634:Aminoquinolines; D002118:Calcium / Q000097:blood*; D002460:Cell Line; D005456:Fluorescent Dyes; D006801:Humans; D007700:Kinetics; D037102:Lectins / Q000494:pharmacology*; D007945:Leukemia, Lymphoid; D008213:Lymphocyte Activation; D008564:Membrane Potentials / Q000187:drug effects; D011188:Potassium / Q000494:pharmacology; D012397:Rosette Formation; D013601:T-Lymphocytes / Q000166:cytology / Q000276:immunology* / Q000378:metabolism
D000634:Aminoquinolines; D005456:Fluorescent Dyes; D037102:Lectins; C035739:Quin2; D011188:Potassium; D002118:Calcium