Figure 12.

Effect of several potassium channel blockers on the I_K(Ca) of the AS-HEL cells. I_K(Ca) was activated by dialyzing AS-HEL cells with an internal solution containing 1 μM Ca²⁺. (a) Once I_K(Ca) was activated, the cells were superfused with an external solution containing either 10 μM quinine, 10 mM TEA, 100 nM apamin, 100 μM d-tubocurarine (d-TC) or 1 μM clotrimazole (CLT). Data are shown as mean ± SEM (four cells in each group) of the outward current elicited by a voltage step to +60 mV from a holding potential of −80 mV, before (solid column) or during (open column) exposure to the indicated potassium channel blocker. I_K(Ca) is significantly inhibited by 1 μM clotrimazole and 10 mM TEA (*P < 0.05, paired t test). (b) AS-HEL cells were superfused with different concentrations of CTX after activation of the I_K(Ca). Current–voltage relationship shows the shift of reversal potentials upon CTX treatment (four to six cells in each group). (c) The data from b for the voltage step to +60 mV are replotted as a function of the concentration of CTX. The data were fit using the Hill equation: I = I _max/[1 + (C _1/2/C)ⁿ] with n = 0.9 and C _1/2 = 21 nM.