Figure 3. Comparison of gating properties of Kv2.1 homomers and Kv2.1:Kv6.4 heteromers. (A) Example currents recorded under TEVC from oocytes expressing Kv2.1 (left) or Kv2.1:Kv6.4 (right) in response to 400-ms depolarizations ranging from −60 to +40 mV in 20-mV increments from a holding potential of −100 mV. Tail currents were recorded at −50 mV. Scale bars are included for current amplitude and time and the voltage protocol is shown below the currents. The step to 0 mV is highlighted in magenta to emphasize the left-shift in voltage activation in Kv2.1:Kv6.4. For Kv2.1:6.4, a 1:10 cRNA ratio was used for the experiments in this figure to produce a predominantly heteromeric current (Fig. 8). (B) Normalized GV relationships determined from isochronal tail currents recorded at −50 mV after 400-ms steps to the indicated voltages are shown for Kv2.1 (black, n = 7) and Kv2.1:Kv6.4 (magenta, n = 10). Data points show mean, error bars indicate standard error, and smooth curves represent a single Boltzmann fit of the data. V50 and slope values are given in Table 1. The V50 values were significantly different (t test, P < 0.001). (C) Example currents recorded from oocytes for Kv2.1 and Kv2.1:Kv6.4 during a protocol used to determine SSI. Oocytes were stepped from a holding potential of −100 mV to voltages ranging from −110 to +30 mV in 10-mV increments for 4 s before a 500-ms step to +40 ms to measure current size. For display purposes, here we show currents recorded in response to prepulses from −40 to +20 mV in 20 mV increments for Kv2.1, and from −100 to −40 mV in 20-mV increments for Kv2.1:Kv6.4. The −40 mV sweep is highlighted in magenta for comparison and represents a voltage at which SSI is virtually absent in Kv2.1 and near maximal in Kv2.1:Kv6.4. Thus, a comparison of currents recorded at +40 mV after prepulses to −100 mV and −40 mV can be used to distinguish homomeric and heteromeric current fractions. Scale bars are given for time and current amplitude, and the voltage protocol is shown below the currents. (D) Normalized SSI curves for Kv2.1 (black, n = 7) and Kv2.1:Kv6.4 (magenta, n = 10). Data show mean ± SEM, and curves show a single Boltzmann fit of the data. V50 and slope values are given in Table 1. Note SSI is incomplete for both Kv2.1 and Kv2.1:Kv6.4; residual pedestal current fractions as determined by Boltzmann fitting are given in Table 1.
Figure 3.

Comparison of gating properties of Kv2.1 homomers and Kv2.1:Kv6.4 heteromers. (A) Example currents recorded under TEVC from oocytes expressing Kv2.1 (left) or Kv2.1:Kv6.4 (right) in response to 400-ms depolarizations ranging from −60 to +40 mV in 20-mV increments from a holding potential of −100 mV. Tail currents were recorded at −50 mV. Scale bars are included for current amplitude and time and the voltage protocol is shown below the currents. The step to 0 mV is highlighted in magenta to emphasize the left-shift in voltage activation in Kv2.1:Kv6.4. For Kv2.1:6.4, a 1:10 cRNA ratio was used for the experiments in this figure to produce a predominantly heteromeric current (Fig. 8). (B) Normalized GV relationships determined from isochronal tail currents recorded at −50 mV after 400-ms steps to the indicated voltages are shown for Kv2.1 (black, n = 7) and Kv2.1:Kv6.4 (magenta, n = 10). Data points show mean, error bars indicate standard error, and smooth curves represent a single Boltzmann fit of the data. V50 and slope values are given in Table 1. The V50 values were significantly different (t test, P < 0.001). (C) Example currents recorded from oocytes for Kv2.1 and Kv2.1:Kv6.4 during a protocol used to determine SSI. Oocytes were stepped from a holding potential of −100 mV to voltages ranging from −110 to +30 mV in 10-mV increments for 4 s before a 500-ms step to +40 ms to measure current size. For display purposes, here we show currents recorded in response to prepulses from −40 to +20 mV in 20 mV increments for Kv2.1, and from −100 to −40 mV in 20-mV increments for Kv2.1:Kv6.4. The −40 mV sweep is highlighted in magenta for comparison and represents a voltage at which SSI is virtually absent in Kv2.1 and near maximal in Kv2.1:Kv6.4. Thus, a comparison of currents recorded at +40 mV after prepulses to −100 mV and −40 mV can be used to distinguish homomeric and heteromeric current fractions. Scale bars are given for time and current amplitude, and the voltage protocol is shown below the currents. (D) Normalized SSI curves for Kv2.1 (black, n = 7) and Kv2.1:Kv6.4 (magenta, n = 10). Data show mean ± SEM, and curves show a single Boltzmann fit of the data. V50 and slope values are given in Table 1. Note SSI is incomplete for both Kv2.1 and Kv2.1:Kv6.4; residual pedestal current fractions as determined by Boltzmann fitting are given in Table 1.

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