Acute actions of tumor necrosis factor-alpha on intracellular Ca(2+) and K(+) currents in human microglia.
The effects of acute application of the pro-inflammatory cytokine tumor necrosis factor-alpha (TNFalpha) on levels of intracellular Ca(2+) ([Ca(2+)]i) and on whole-cell outward and inward K(+) currents were studied in cultured human microglia. TNFalpha elicited a linear increase in [Ca(2+)]i to a plateau level in microglia bathed in either standard physiological saline solution or Ca(2+)-free physiological saline solution. The rate of increase of [Ca(2+)]i or the level of [Ca(2+)]i attained was not significantly altered in the absence of external Ca(2+) indicating that Ca(2+) influx did not contribute appreciably to the cytokine-induced rise in [Ca(2+)]i. This point was directly confirmed using Mn(2+) quenching where no change in signal fluorescence was observed with TNFalpha treatment of microglia in Ca(2+)-free physiological saline solution. The rate of increase of [Ca(2+)]i induced by TNFalpha in Ca(2+)-free physiological saline solution was not altered by prior application of ATP to deplete inositol triphosphate stores indicating that these stores did not contribute to the cytokine response. In whole-cell patch clamp recordings, the acute treatment of human microglia with TNFalpha led to the expression of an outward K(+) current in one-third (14 of 41) of cells. This current was activated at potentials positive to -30 mV, showed rapid kinetics of activation with no evident inactivation and had an I-V relation exhibiting outward rectification. Analysis of tail currents showed reversal of the outward K(+) current near -70 mV and tetraethylammonium (10 mM) inhibited the outward K(+) current to 24% of control level. Acute application of TNFalpha had no effect to alter inward rectifier currents generated from voltage ramps. The signaling pathways involving TNFalpha modulation of [Ca(2+)]i and K(+) channels in human microglia may contribute to functional and pathological actions of the cytokine in the brain.
McLarnon
J G
JG
Department of Pharmacology and Therapeutics, Faculty of Medicine, The University of British Columbia, Vancouver, BC, Canada V6T 1Z3. mclarnon@interchange.ubc.ca
Franciosi
S
S
Wang
X
X
Bae
J H
JH
Choi
H B
HB
Kim
S U
SU
D000255:Adenosine Triphosphate / Q000378:metabolism / Q000494:pharmacology; D001921:Brain / Q000166:cytology / Q000378:metabolism / Q000503:physiopathology; D002118:Calcium / Q000172:deficiency; D015220:Calcium Channels / Q000187:drug effects* / Q000378:metabolism; D020013:Calcium Signaling / Q000187:drug effects* / Q000502:physiology; D002478:Cells, Cultured / Q000187:drug effects / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004660:Encephalitis / Q000378:metabolism* / Q000503:physiopathology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005333:Fetus; D006801:Humans; D007211:Indoles / Q000494:pharmacology; D007424:Intracellular Fluid / Q000187:drug effects* / Q000378:metabolism; D008345:Manganese / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D017628:Microglia / Q000187:drug effects* / Q000378:metabolism; D008856:Microscopy, Fluorescence; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000187:drug effects* / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D013050:Spectrometry, Fluorescence; D019789:Tetraethylammonium / Q000494:pharmacology; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*
D015220:Calcium Channels; D004791:Enzyme Inhibitors; D007211:Indoles; D015221:Potassium Channels; D014409:Tumor Necrosis Factor-alpha; D008345:Manganese; D019789:Tetraethylammonium; D000255:Adenosine Triphosphate; D002118:Calcium; C000543:cyclopiazonic acid