An amiloride-sensitive and voltage-dependent Na+ channel in an HLA-DR-restricted human T cell clone
Z F Lai1, Y Z Chen, Y Nishimura
1Department of Pharmacology, Kumamoto University School of Medicine, Japan. lai-zf@gpo.kumamoto-u.ac.jp
Insights
Antigen stimulation activates voltage-gated sodium channels in T cells, crucial for proliferation. Amiloride inhibits these sodium currents and T cell responses, highlighting their role in immune activation.
Area of Science:
- Immunology
- Cellular Physiology
- Molecular Biology
Background:
- T cell activation is a complex process involving numerous signaling pathways.
- Voltage-gated ion channels play critical roles in cellular functions, including immune cell responses.
Purpose of the Study:
- To investigate the role of voltage-gated sodium (Na+) currents in human T cell activation.
- To examine the effect of extracellular Na+ on T cell proliferation.
Main Methods:
- Whole-cell patch-clamp electrophysiology was used to record ion currents in T cells.
- T cells were stimulated with an antigenic peptide in the presence or absence of extracellular Na+.
- Cell proliferation assays were performed under varying extracellular Na+ conditions and in the presence of amiloride.
Main Results:
- Antigenic peptide stimulation induced voltage-dependent inward Na+ currents in 31% of T cells.
- These Na+ currents were inhibited by amiloride but not tetrodotoxin.
- T cell proliferation was inhibited in Na+-free conditions and suppressed by amiloride.
Conclusions:
- Activation of amiloride-sensitive, voltage-gated Na+ channels is essential for T cell activation and proliferation.
- Na+ influx through these channels may be critical for maintaining intracellular Ca2+ levels during T cell activation.
Abstract:
We investigated changes in voltage-gated Na+ currents and effects of extracellular Na+ on proliferation in HLA-DR-restricted human CD4+ alphabeta T cells after stimulation with a non-self antigenic peptide, M12p54-68. In the absence of antigenic peptide, neither single (n = 80) nor APC-contacted (n = 71) T cells showed voltage-gated inward currents recording with whole-cell patch-clamp techniques, even with Ca2+ and Na+ ions present in the perfusion solution. However, with the same recording conditions, 31% (26 of 84) of APC-contacted T cells stimulated with the antigenic peptide showed voltage-dependent inward currents that were elicited from -60 mV. The inward currents were not inhibited in extracellular Ca2+-free conditions or in the presence of 1 mM NiCl2. However, they were completely inhibited in extracellular Na+-free conditions, which were made by replacing Na+ with iso-osmotic N-methyl-d -glucamine or choline. The Na+ currents were insensitive to tetrodotoxin, a classical blocker of Na+ channels, but were dose-dependently inhibited by amiloride, a potassium-sparing pyrazine diuretic. Furthermore, the Ag-specific proliferative response of T cells was completely inhibited in Na+-free Tyrode's solution and was suppressed by amiloride in a dose-dependent manner. Our findings suggest that activation of amiloride-sensitive and voltage-gated Na+ channels would be an important step to allow an adequate influx of Na+ and maintain a sustained high Ca2+ level during T cell activation.
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