Figure 3.

SMase D activates native K_V1.3 channels in human T cells. (A) K_V1.3 currents of a T cell recorded in the presence of 5 mM [K⁺]_ext elicited by stepping the voltage every 15 s from the −100-mV holding potential to the −40-mV test potential. After the addition of SMase D, the current gradually increased. (B) Time course of K_V1.3 current increase after the addition of SMase D. (C and D) K_V1.3 currents ([K⁺]_ext = 20 mM) elicited by stepping the membrane voltage from the −100-mV holding potential to between −80 and 10 mV in 10-mV increments at 15-s intervals before (C) and after (D) the addition of SMase D to the bath solution, where the current traces for −30 mV are colored maroon. Dashed lines in A, C, and D indicate zero current levels. (E–H) G-V curves of K_V1.3 channels in T cells (E and F) and Jurkat cells (G and H) before (open squares) and after (closed circles) either a 3-min treatment with SMase D (E and G) or a 3-min control period in the absence of SMase D (F and H), where all data are presented as means ± SEM (n = 5). The curves are fits of Boltzmann functions, yielding V_1/2 = −26.1 ± 0.4 mV and Z = 3.7 ± 0.2 (open squares), or V_1/2 = −42.4 ± 0.6 mV and Z = 4.0 ± 0.3 (closed circles) for E; V_1/2 = −27.0 ± 0.4 mV and Z = 3.8 ± 0.2 (open squares) or V_1/2 = −33.2 ± 0.5 mV and Z = 4.1 ± 0.3 (closed circles) for F; V_1/2 = −28.8 ± 0.4 mV and Z = 4.3 ± 0.2 (open squares) or V_1/2 = −38.6 ± 0.3 mV and Z = 4.5 ± 0.2 (closed circles) for G; and V_1/2 = −30.6 ± 0.5 mV and Z = 3.5 ± 0.2 (open squares) or V_1/2 = −32.1 ± 0.5 mV and Z = 3.6 ± 0.2 (closed circles) for H.