Figure 6.

Cav3‐F97C coexpression decreases I_Kv4.2 density, alters kinetics and slows recovery from inactivation

A, representative I _Kv4.2 current traces measured at −40, 0, 40 and 60 mV in HEK293 cells transfected with K_v4.2 and Cav3‐WT or Cav3‐F97C. Whole‐cell currents were recorded using the protocol indicated in the inset. B, mean I–V relationships for peak I _Kv4.2 density in transfected HEK293 cells with K_v4.2 and Cav3‐WT or Cav3‐F97C (mean ± SEM, n = 13–23 cells, ^**P < 0.01, ^*P < 0.05). C, representative I _Kv4.2 traces normalized to the peak current measured at 40 mV from cells expressing Cav3‐WT or Cav3‐F97C. D, average τ activation for I _Kv4.2 from Cav3‐WT and Cav3‐F97C expressing cells as a function of test voltage (mean ± SEM, n = 13–23 cells, ^***P < 0.005, ^**P < 0.01, ^*P < 0.05). τ activation determined by fitting a single exponential function to the rising phase (activation) of I _Kv4.2. E and F, average τ_fast inactivation and τ_slow inactivation for I _Kv4.2 as determined by fitting a double exponential function to the decaying phase of I _Kv4.2 traces (mean ± SEM, n = 13–23 cells, ^***P < 0.005, ^**P < 0.01, ^*P < 0.05). G, average fractional amplitude of fast inactivating (τ_fast) I _Kv4.2 at 40 mV comparing Cav3‐WT and Cav3‐F97C (mean ± SEM, n = 13‐23, P < 0.005). H, representative I _Kv4.2 traces demonstrating recovery from inactivation following a 2 s depolarization to 40 mV with co‐expression of Cav3‐WT or Cav3‐F97C. I, time course of recovery from inactivation for I _Kv4.2 currents in Cav3‐WT and Cav3‐F97C expressing cells. Ratio between the current amplitude obtained with both pulses of the protocol is plotted against the interpulse interval. Recovery time constant for Cav3‐WT was 331 ± 40 ms (n = 6) compared to 809 ± 83 ms (n = 5) Cav3‐F97C (P < 0.001).