Figure 9. Characterization of voltage-dependent currents elicited by co-expression of K_V11.1 demi-channels carrying a Δ138–373 deletion.

(a) Voltage-dependent activation of K_V11.1 C-terminal and N-terminal demi-channels carrying a Δ138–373 deletion corresponding to the proximal domain located at the cytoplasmic segment, preceding helix S1 in the initial half of the voltage sensor module. Left panel, raw current traces recorded in 50 mM extracellular K⁺ in response to the voltage protocol shown at the top. Right panel, plot of normalized peak tail currents as a function of depolarizing voltage. A curve from non-deleted split channels obtained in the same conditions is shown as a dotted line for comparison. Error bars represent s.e. (b) Determination of voltage-dependent activation rates. Left panels, time course of current activation at 0 mV studied in 50 mM extracellular K⁺. Representative currents recorded in response to the illustrated voltage protocol are shown at the top. A plot of normalized peak current value versus depolarization time at 0 mV is shown at the bottom. The time necessary to attain half-maximum current magnitude is marked with a dashed arrow. Right panel, dependence of activation rates on depolarization membrane potential. Values from wild-type non-split channels (Wild type continuous), non-deleted split channels (Y545 Split) and non-split channels lacking the proximal domain at the amino terminus (Δ138–373 continuous) are also shown for comparison. (c) Voltage-dependent deactivation. Left panel, representative current traces recorded in 50 mM extracellular K⁺ during steps to potentials ranging from −20 to −140 mV with the voltage protocol schematized at the top. An enhanced view of the peak tail currents during the repolarization steps is shown in the inset. Right panel, plot of fast deactivation time constant for different repolarization voltages. Values from wild-type non-split channels (wild-type continuous) and non-deleted split channels (Y545 Split) are also shown for comparison.