Figure 6.

Effects of Ba²⁺ and Cs⁺/Cd²⁺ on bEAG1 currents. (A) Current traces recorded from a HEK 293 cell expressing bEAG1 channels; the extracellular solution contained 5 mM Ba²⁺ as the only divalent cation. Depolarizing voltage pulses of 1.5-s duration were applied from the holding voltage (−70 mV) to +80 mV in steps of 10 mV. To establish a steady state Ba²⁺ effect, eight pulses to +45 mV were applied before starting the pulse protocol. All pulses were applied in 15-s intervals. (B) Voltage dependence of channel activation in the presence of 5 mM Ba²⁺. Peak currents (•), and currents measured at the end of the 1.5-s pulses (▴) are normalized to the peak current at V_m = +80 mV (mean values ± SD from five cells). (C) Use dependence of Ba²⁺ effect on bEAG1. After 10 min in extracellular solution containing 5 mM Ba²⁺, the whole-cell configuration was established and depolarizing voltage pulses were applied in 15-s intervals from the holding voltage (−70 mV) to +45 mV. The numbers on the right of each trace indicate the sequence of pulses. For removal of Ba²⁺, the bath was perfused with extracellular solution without added divalent cations. (D) Exposure to Ca²⁺, Mg²⁺, or Sr²⁺ (5 mM) in the extracellular solution prevents Ba²⁺-dependent inactivation. The top trace in each panel shows the fifth depolarizing pulse (−70 to +45 mV) in the presence of the indicated divalent cation, but without Ba²⁺. After exchanging the test ion for 5 mM Ba²⁺, five pulses were applied in 15-s intervals, and the fifth pulse is superimposed for comparison. A reduction of current amplitude, but not inactivation, is observed with Ba²⁺ for the cells previously exposed to Ca²⁺, Mg²⁺, or Sr²⁺. In contrast, when no divalent cations were added during the first five pulses, subsequent pulses in 5 mM Ba²⁺ showed stronger suppression and almost complete inactivation of bEAG1 current. (E) Outward current conducted by bEAG1 in the presence of 5 mM Cs⁺ and 0.1 mM Cd²⁺ in the extracellular solution containing 0.5 mM Mg²⁺. Holding voltage was −70 mV; voltage steps in increments of +10 mV were applied for 1.5 s. In Cs⁺/Cd²⁺-free standard solution, this cell displayed a steady state current of 4.8 nA at +40 mV.