Figure 4. Steady-state inactivation and deactivation of HERG currents are not affected by mild cholesterol enrichment. Cells were incubated with 25 μM MβCD-cholesterol for 1–2 h at 37 °C before recordings. (A) To measure the voltage-dependence of steady-state inactivation, channels were activated by prolonged depolarization to +20 mV followed by a brief hyperpolarizing step to -120 mV and then depolarization to various potentials. The voltage protocol is shown in the inset. Current traces were fit with single exponential equation to obtain τinactivation. (B) Summary data of voltage-dependence of rates of inactivation showing that the mild cholesterol enrichment slows the rate of inactivation only at depolarizing voltage over +10 mV (n = 5). Open circles: control cells. Closed circles: cells treated with 25 μM MβCD-cholesterol. *p < 0.05 (C) Deactivation of HERG current was measured. Currents were stimulated by a 2 sec prepulse to −40 mV, followed by test pulses ranging from −120 to −20 mV for 3 sec. The voltage protocol is shown in the inset. Current traces were fit with two exponential equations to obtain τdeactivation. (D) Summary of deactivation kinetic analysis shows that mild cholesterol enrichment induced no significant changes in both the fast time constant (τfast), and the fast time constant (τslow) (n = 5).