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Voltage-dependent gating and gating charge measurements in the Kv1.2 potassium channel.

Ishida IG, Rangel-Yescas GE, Carrasco-Zanini J, Islas LD - J. Gen. Physiol. (2015)

Bottom Line: We found that the Kv1.2 gating charge is near 10 elementary charges (eo), ∼25% less than the well-established 13-14 eo in Shaker.Next, we neutralized positive residues in the Kv1.2 S4 transmembrane segment to investigate the cause of the reduction of the gating charge and found that, whereas replacing R1 with glutamine decreased voltage sensitivity to ∼50% of the wild-type channel value, mutation of the subsequent arginines had a much smaller effect.These data are in marked contrast to the effects of charge neutralization in Shaker, where removal of the first four basic residues reduces the gating charge by roughly the same amount.

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Affiliation: Departamento de Fisiología, Facultad de Medicina, Universidad Nacional Autónoma de México, Distrito Federal 04510, México.

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Gating currents and charge movement. (A) Gating current traces recorded from a cell-attached patch. Traces shown correspond to −80, −60, −40, −20, 0, and 20 mV from a holding potential of −90 mV. (B) Voltage dependence of the normalized charge movement from five different patches. Charge was determined from the time integral of traces as in A. The red curve is a fit of a sum of two Boltzmann functions with charges q1 = 0.3 eo, q2 = 3 eo, and V11/2 = −70 mV, V21/2 = −37 mV. Error bars are the SEM. (C) Time constant of current decay τon determined from an exponential fit to the gating current decay; n = 5 patches. The red line is the average fit of Eq. 3 to all five patches; the partial charge is qon = 0.54 eo. (D) Time constant of the off-gating current decay determined from an exponential fit. Note that the time constant becomes very slow and voltage independent at voltages more positive than 40 mV, which corresponds to the range of channel opening.
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fig2: Gating currents and charge movement. (A) Gating current traces recorded from a cell-attached patch. Traces shown correspond to −80, −60, −40, −20, 0, and 20 mV from a holding potential of −90 mV. (B) Voltage dependence of the normalized charge movement from five different patches. Charge was determined from the time integral of traces as in A. The red curve is a fit of a sum of two Boltzmann functions with charges q1 = 0.3 eo, q2 = 3 eo, and V11/2 = −70 mV, V21/2 = −37 mV. Error bars are the SEM. (C) Time constant of current decay τon determined from an exponential fit to the gating current decay; n = 5 patches. The red line is the average fit of Eq. 3 to all five patches; the partial charge is qon = 0.54 eo. (D) Time constant of the off-gating current decay determined from an exponential fit. Note that the time constant becomes very slow and voltage independent at voltages more positive than 40 mV, which corresponds to the range of channel opening.

Mentions: We recorded voltage-dependent charge movement from cell-attached patches in the absence of permeant ions. Gating currents could be observed in patches from oocytes with very high expression levels and were apparent at voltages more negative than those that induce significant channel opening, as expected for a channel where charge movement is coupled to channel opening (Fig. 2 A). The charge obtained from integration of currents during depolarization (on-gating currents) was discernible at voltages as negative as −80 mV and became saturated at voltages positive to −10 mV. The Q(V) relationship could be fit by a sum of two Boltzmann equations (Fig. 2 B). The voltage dependence of charge movement is reminiscent of that in Shaker (Zagotta et al., 1994b; Schoppa and Sigworth, 1998a).


Voltage-dependent gating and gating charge measurements in the Kv1.2 potassium channel.

Ishida IG, Rangel-Yescas GE, Carrasco-Zanini J, Islas LD - J. Gen. Physiol. (2015)

Gating currents and charge movement. (A) Gating current traces recorded from a cell-attached patch. Traces shown correspond to −80, −60, −40, −20, 0, and 20 mV from a holding potential of −90 mV. (B) Voltage dependence of the normalized charge movement from five different patches. Charge was determined from the time integral of traces as in A. The red curve is a fit of a sum of two Boltzmann functions with charges q1 = 0.3 eo, q2 = 3 eo, and V11/2 = −70 mV, V21/2 = −37 mV. Error bars are the SEM. (C) Time constant of current decay τon determined from an exponential fit to the gating current decay; n = 5 patches. The red line is the average fit of Eq. 3 to all five patches; the partial charge is qon = 0.54 eo. (D) Time constant of the off-gating current decay determined from an exponential fit. Note that the time constant becomes very slow and voltage independent at voltages more positive than 40 mV, which corresponds to the range of channel opening.
© Copyright Policy - openaccess
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4380214&req=5

fig2: Gating currents and charge movement. (A) Gating current traces recorded from a cell-attached patch. Traces shown correspond to −80, −60, −40, −20, 0, and 20 mV from a holding potential of −90 mV. (B) Voltage dependence of the normalized charge movement from five different patches. Charge was determined from the time integral of traces as in A. The red curve is a fit of a sum of two Boltzmann functions with charges q1 = 0.3 eo, q2 = 3 eo, and V11/2 = −70 mV, V21/2 = −37 mV. Error bars are the SEM. (C) Time constant of current decay τon determined from an exponential fit to the gating current decay; n = 5 patches. The red line is the average fit of Eq. 3 to all five patches; the partial charge is qon = 0.54 eo. (D) Time constant of the off-gating current decay determined from an exponential fit. Note that the time constant becomes very slow and voltage independent at voltages more positive than 40 mV, which corresponds to the range of channel opening.
Mentions: We recorded voltage-dependent charge movement from cell-attached patches in the absence of permeant ions. Gating currents could be observed in patches from oocytes with very high expression levels and were apparent at voltages more negative than those that induce significant channel opening, as expected for a channel where charge movement is coupled to channel opening (Fig. 2 A). The charge obtained from integration of currents during depolarization (on-gating currents) was discernible at voltages as negative as −80 mV and became saturated at voltages positive to −10 mV. The Q(V) relationship could be fit by a sum of two Boltzmann equations (Fig. 2 B). The voltage dependence of charge movement is reminiscent of that in Shaker (Zagotta et al., 1994b; Schoppa and Sigworth, 1998a).

Bottom Line: We found that the Kv1.2 gating charge is near 10 elementary charges (eo), ∼25% less than the well-established 13-14 eo in Shaker.Next, we neutralized positive residues in the Kv1.2 S4 transmembrane segment to investigate the cause of the reduction of the gating charge and found that, whereas replacing R1 with glutamine decreased voltage sensitivity to ∼50% of the wild-type channel value, mutation of the subsequent arginines had a much smaller effect.These data are in marked contrast to the effects of charge neutralization in Shaker, where removal of the first four basic residues reduces the gating charge by roughly the same amount.

View Article: PubMed Central - HTML - PubMed

Affiliation: Departamento de Fisiología, Facultad de Medicina, Universidad Nacional Autónoma de México, Distrito Federal 04510, México.

Show MeSH
Related in: MedlinePlus