Figure 3. HERG current activation is similar in 5 mm K₀⁺ and 135 mm Cs₀⁺.

The values for activation time constants (τ_act) were determined by fitting the envelopes of the extrapolated peak amplitude of tail currents recorded at −50 mV after varying duration depolarizations to between −20 and +80 mV from a holding potential of −80 mV. The protocol for a depolarization to +60 mV is shown above panel A. The internal solution contained 130 mm K⁺. A and B show envelopes of tail currents elicited by a depolarization to 60 mV with variable duration in external solution containing 5 mm K₀⁺ (A) or 135 mm Cs₀⁺ (B). C, τ_act was measured from single exponential fits to the extrapolated peak tail current envelope from A (▪) and B (•). The values for τ_act were 149 and 141 ms, respectively. D, the voltage dependence of τ_act in external solution containing 5 mm K₀⁺ (▪) or 135 mm Cs₀⁺ (•) (n = 5–8).