An Amiloride-Sensitive and Voltage-Dependent Na+ Channel in an HLA-DR-Restricted Human T Cell Clone

Abstract

We investigated changes in voltage-gated Na+ currents and effects of extracellular Na+ on proliferation in HLA-DR-restricted human CD4+ αβ 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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“…We administered amiloride in vivo and showed reduction in the magnitude of CII-specific, but not polyclonal, T cell responses in draining lymph nodes, suggesting that under these experimental conditions amiloride did not directly affect the T cell response, as has been reported in other experimental settings [52,53]. Our data suggest that amiloride caused an immunosuppressive effect on T cell activation in vivo indirectly via inhibition of uptake and antigen presentation, rather than via a direct suppression of T cell proliferation [52,53] Amiloride has also been shown to block soluble urokinase-type plasminogen activator [54], a serine proteinase expressed by macrophages and DCs (our unpublished observations), suggesting another mechanism underlying the effect of this drug on antigen presentation.…”

Loss of Na+ channel β2 subunits is neuroprotective in a mouse model of multiple sclerosis

“…EAE is considered to be a T cell-mediated autoimmune disease model (Kuchroo et al, 2002) and there is some evidence suggesting a role for Na + channels in T cells (Khan and Poisson, 1999; Lai et al, 2000). Abnormal activation of T cells is thus another possible explanation for the milder symptoms of EAE observed in the null mice.…”

Axonal protection achieved in a model of multiple sclerosis using lamotrigine

“…Specifically, therapeutically relevant doses of lamotrigine reduced lymph node cell proliferation in response to PHA [41]. A role for sodium currents in T cell activation and costimulation has been suggested [21,30,33]. These findings suggest that the improvements in neurological function and increased axonal survival may be due to a reduction in disease severity.…”