Activation of Ca2+-dependent K+ channels in human B lymphocytes by anti-immunoglobulin.
Many mammalian cell types exhibit Ca2+-dependent K+ channels, and activation of these channels by increasing intracellular calcium generally leads to a hyperpolarization of the plasma membrane. Their presence in B lymphocytes is as yet uncertain. Crosslinking Ig on the surface of B lymphocytes is known to increase the level of free cytoplasmic calcium ([Ca2+]i). However, rather than hyperpolarization, a depolarization has been reported to occur after treatment of B lymphocytes with anti-Ig. To determine if Ca2+-dependent K+ channels are present in B lymphocytes, and to examine the relationship between intracellular free calcium and membrane potential, we monitored [Ca2+]i by means of indo-1 and transmembrane potential using bis(1,3-diethylthiobarbituric)trimethine oxonol in human tonsillar B cells activated by anti-IgM. Treatment with anti-IgM induced a biphasic increase in [Ca2+]i and a simultaneous hyperpolarization. A similar hyperpolarization was induced by ionomycin, a Ca2+ ionophore. Delaying the development of the [Ca2+]i response by increasing the cytoplasmic Ca2+-buffering power delayed the hyperpolarization. Conversely, eliminating the sustained phase of the [Ca2+]i response by omission of external Ca2+ abolished the prolonged hyperpolarization. In fact, a sizable Na+-dependent depolarization was unmasked. This study demonstrates that in human B lymphocytes, Ca2+-dependent K+ channels can be activated by crosslinking of surface IgM. Moreover, it is likely that, by analogy with voltage-sensitive Ca2+ channels, Na+ can permeate through these ligand-gated Ca2+ "channels" in the absence of extracellular Ca2+.
D000888:Antibodies, Anti-Idiotypic / Q000276:immunology; D001402:B-Lymphocytes / Q000502:physiology*; D002118:Calcium / Q000502:physiology*; D002462:Cell Membrane / Q000502:physiology; D003593:Cytoplasm / Q000502:physiology; D004553:Electric Conductivity; D006801:Humans; D007473:Ion Channels / Q000502:physiology*; D008564:Membrane Potentials; D011188:Potassium / Q000502:physiology*; D011947:Receptors, Antigen, B-Cell / Q000502:physiology*; D013997:Time Factors; D001613:beta 2-Microglobulin / Q000502:physiology
D000888:Antibodies, Anti-Idiotypic; D007473:Ion Channels; D011947:Receptors, Antigen, B-Cell; D001613:beta 2-Microglobulin; D011188:Potassium; D002118:Calcium