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. 2008 Mar;131(3):257–273. doi: 10.1085/jgp.200709938

Figure 2.

Figure 2.

Q-immobilization at hyperpolarized potentials. (A) Simulation assuming an “inactivation-less” Kv channel (based on the ZHA model for Δ6–46 Shaker-B channels; see text) predicts that the QONV (black line) and available 1 − QONV (gray line) curves cross at their midpoints. (B) Available Q (hollow circles in C and D) was assayed in Kv4.2 channels by a step depolarization to +37 mV after a 900-ms prepulse between −153 and −33 mV in 10-mV increments from a holding potential of −153 mV. Inset, Kv4.2 gating currents elicited by 12-ms step depolarizations between −143 and +37 mV in 10-mV increments from a holding potential of −153 mV. (C) The above protocol was applied to mutant Shaker-B channels (W434F-T449V). For comparison, the QONV, 1 − QONV, and the Q-availability curves are shown superimposed. Data were described by assuming a Boltzmann function with the following best-fit parameters for the QONV curve: V 1/2 = −44.2 mV, z = 2.8 e0; and the Q-availability curve: V 1/2 = −53.6 mV, z = 2.8 e0, n = 4. (D) QV curves from Kv4.2 channels were described by Boltzmann functions assuming the following parameters for the QONV: V 1/2 = −43.0 mV, z = 3.4 e0; and the Q-availability curve: V 1/2 = −91.2 mV, z = 3.5 e0, n = 7. The ΔV between these curves is 48 mV.