Limits...
An electrostatic potassium channel opener targeting the final voltage sensor transition.

Börjesson SI, Elinder F - J. Gen. Physiol. (2011)

Bottom Line: However, molecular details for the interaction between PUFA and ion channels are not well understood.In this study, we have localized the site of action for PUFAs on the voltage-gated Shaker K channel by introducing positive charges on the channel surface, which potentiated the PUFA effect.Furthermore, we found that PUFA mainly affects the final voltage sensor movement, which is closely linked to channel opening, and that specific charges at the extracellular end of the voltage sensor are critical for the PUFA effect.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Clinical and Experimental Medicine, Division of Cell Biology, Linköping University, Sweden.

ABSTRACT
Free polyunsaturated fatty acids (PUFAs) modulate the voltage dependence of voltage-gated ion channels. As an important consequence thereof, PUFAs can suppress epileptic seizures and cardiac arrhythmia. However, molecular details for the interaction between PUFA and ion channels are not well understood. In this study, we have localized the site of action for PUFAs on the voltage-gated Shaker K channel by introducing positive charges on the channel surface, which potentiated the PUFA effect. Furthermore, we found that PUFA mainly affects the final voltage sensor movement, which is closely linked to channel opening, and that specific charges at the extracellular end of the voltage sensor are critical for the PUFA effect. Because different voltage-gated K channels have different charge profiles, this implies channel-specific PUFA effects. The identified site and the pharmacological mechanism will potentially be very useful in future drug design of small-molecule compounds specifically targeting neuronal and cardiac excitability.

Show MeSH

Related in: MedlinePlus

Effect of DHA on the early activation steps versus the opening step. (A) A simple scheme for the ion channel kinetics. C0 to C4 denote closed states with 0–4 activated voltage sensors where the voltage sensors move independently of each other. O is the open state. (B) Theoretical G-V curves and Q-V curves for WT-IR and the ILT channel generated from the model in A. For calculations, see Eqs. 4–7 in Materials and methods. (C) 70 µM DHA at pH 9.0 increases the ion current at +60 mV in the ILT channel. Holding voltage is −80 mV. (D) The G-V curve is shifted −30 mV for the ILT channel. Eq. 2 is fitted to the experimental data as explained in Materials and methods. V1/2 = 118 mV for control and 88 mV for DHA. s = 22.6 mV and A = 0.271 mS in both curves. (E) Integrated OFF gating currents from the ILT/W434F mutation (n = 3). 70 µM DHA at pH 9.0 shifts the control curve −5 mV. (F and G) Calculated effects of DHA on open probability (F; G-V) and gating charge movement (G; Q-V) using Eqs. 4–7. Continuous lines are control curves. Dashed curves are DHA-affected curves. DHA was set to shift Vαβ with −5 mV and Vγδ with −30 mV for both channels. (H) Summary of DHA-induced shifts from both experiments and models. Data are expressed as mean ± SEM (n = 3–9).
© Copyright Policy - openaccess
Related In: Results  -  Collection

License 1 - License 2
getmorefigures.php?uid=PMC3105513&req=5

fig5: Effect of DHA on the early activation steps versus the opening step. (A) A simple scheme for the ion channel kinetics. C0 to C4 denote closed states with 0–4 activated voltage sensors where the voltage sensors move independently of each other. O is the open state. (B) Theoretical G-V curves and Q-V curves for WT-IR and the ILT channel generated from the model in A. For calculations, see Eqs. 4–7 in Materials and methods. (C) 70 µM DHA at pH 9.0 increases the ion current at +60 mV in the ILT channel. Holding voltage is −80 mV. (D) The G-V curve is shifted −30 mV for the ILT channel. Eq. 2 is fitted to the experimental data as explained in Materials and methods. V1/2 = 118 mV for control and 88 mV for DHA. s = 22.6 mV and A = 0.271 mS in both curves. (E) Integrated OFF gating currents from the ILT/W434F mutation (n = 3). 70 µM DHA at pH 9.0 shifts the control curve −5 mV. (F and G) Calculated effects of DHA on open probability (F; G-V) and gating charge movement (G; Q-V) using Eqs. 4–7. Continuous lines are control curves. Dashed curves are DHA-affected curves. DHA was set to shift Vαβ with −5 mV and Vγδ with −30 mV for both channels. (H) Summary of DHA-induced shifts from both experiments and models. Data are expressed as mean ± SEM (n = 3–9).

Mentions: For the computer simulations of K channel gating, we used a six-state model (Fig. 5 A). C0 to C4 indicate states of the channel with 0–4 activated voltage sensors (S4). The movements of the voltage sensors are independent of each other. From state C4, the channel can open via a final cooperative step that involves all four subunits. The steady-state conditions are determined by α/β and by γ/δ, where(4)α/β= exp((V−Vαβ)zαβFR−1T−1)(5)γ/δ= exp((V−Vγδ)zγδFR−1T−1),Vαβ is the voltage where α = β, Vγδ is the voltage where γ = δ, and zαβ and zγδ are the number of elementary charges moving through the membrane when the channel goes between two closed states or between C4 and O, respectively. Vαβ was set to −40 mV for WT-IR and −80 mV for ILT. Vγδ was set to −40 mV for WT-IR and +100 mV for ILT. zαβ was set to 2 for both WT-IR and for ILT. zγδ was set to 1 for both WT-IR and for ILT. G-V and the gating charge versus voltage curve, Q-V, can easily be computed (see Fig. 5, F and G):(6)G(V)=γ/δ/((α/β)−4+4(α/β)−3+6(α/β)−2+4(α/β)−1+1+γ/δ)(7)Q(V)=4zαβ(α/β)−3+12zαβ(α/β)−2+12zαβ(α/β)−1+4zαβ+(4zαβ+zγδ)γ/δ)/((α/β)−4+4(α/β)−3+6(α/β)−2+4(α/β)−1+1+γ/δ).


An electrostatic potassium channel opener targeting the final voltage sensor transition.

Börjesson SI, Elinder F - J. Gen. Physiol. (2011)

Effect of DHA on the early activation steps versus the opening step. (A) A simple scheme for the ion channel kinetics. C0 to C4 denote closed states with 0–4 activated voltage sensors where the voltage sensors move independently of each other. O is the open state. (B) Theoretical G-V curves and Q-V curves for WT-IR and the ILT channel generated from the model in A. For calculations, see Eqs. 4–7 in Materials and methods. (C) 70 µM DHA at pH 9.0 increases the ion current at +60 mV in the ILT channel. Holding voltage is −80 mV. (D) The G-V curve is shifted −30 mV for the ILT channel. Eq. 2 is fitted to the experimental data as explained in Materials and methods. V1/2 = 118 mV for control and 88 mV for DHA. s = 22.6 mV and A = 0.271 mS in both curves. (E) Integrated OFF gating currents from the ILT/W434F mutation (n = 3). 70 µM DHA at pH 9.0 shifts the control curve −5 mV. (F and G) Calculated effects of DHA on open probability (F; G-V) and gating charge movement (G; Q-V) using Eqs. 4–7. Continuous lines are control curves. Dashed curves are DHA-affected curves. DHA was set to shift Vαβ with −5 mV and Vγδ with −30 mV for both channels. (H) Summary of DHA-induced shifts from both experiments and models. Data are expressed as mean ± SEM (n = 3–9).
© Copyright Policy - openaccess
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC3105513&req=5

fig5: Effect of DHA on the early activation steps versus the opening step. (A) A simple scheme for the ion channel kinetics. C0 to C4 denote closed states with 0–4 activated voltage sensors where the voltage sensors move independently of each other. O is the open state. (B) Theoretical G-V curves and Q-V curves for WT-IR and the ILT channel generated from the model in A. For calculations, see Eqs. 4–7 in Materials and methods. (C) 70 µM DHA at pH 9.0 increases the ion current at +60 mV in the ILT channel. Holding voltage is −80 mV. (D) The G-V curve is shifted −30 mV for the ILT channel. Eq. 2 is fitted to the experimental data as explained in Materials and methods. V1/2 = 118 mV for control and 88 mV for DHA. s = 22.6 mV and A = 0.271 mS in both curves. (E) Integrated OFF gating currents from the ILT/W434F mutation (n = 3). 70 µM DHA at pH 9.0 shifts the control curve −5 mV. (F and G) Calculated effects of DHA on open probability (F; G-V) and gating charge movement (G; Q-V) using Eqs. 4–7. Continuous lines are control curves. Dashed curves are DHA-affected curves. DHA was set to shift Vαβ with −5 mV and Vγδ with −30 mV for both channels. (H) Summary of DHA-induced shifts from both experiments and models. Data are expressed as mean ± SEM (n = 3–9).
Mentions: For the computer simulations of K channel gating, we used a six-state model (Fig. 5 A). C0 to C4 indicate states of the channel with 0–4 activated voltage sensors (S4). The movements of the voltage sensors are independent of each other. From state C4, the channel can open via a final cooperative step that involves all four subunits. The steady-state conditions are determined by α/β and by γ/δ, where(4)α/β= exp((V−Vαβ)zαβFR−1T−1)(5)γ/δ= exp((V−Vγδ)zγδFR−1T−1),Vαβ is the voltage where α = β, Vγδ is the voltage where γ = δ, and zαβ and zγδ are the number of elementary charges moving through the membrane when the channel goes between two closed states or between C4 and O, respectively. Vαβ was set to −40 mV for WT-IR and −80 mV for ILT. Vγδ was set to −40 mV for WT-IR and +100 mV for ILT. zαβ was set to 2 for both WT-IR and for ILT. zγδ was set to 1 for both WT-IR and for ILT. G-V and the gating charge versus voltage curve, Q-V, can easily be computed (see Fig. 5, F and G):(6)G(V)=γ/δ/((α/β)−4+4(α/β)−3+6(α/β)−2+4(α/β)−1+1+γ/δ)(7)Q(V)=4zαβ(α/β)−3+12zαβ(α/β)−2+12zαβ(α/β)−1+4zαβ+(4zαβ+zγδ)γ/δ)/((α/β)−4+4(α/β)−3+6(α/β)−2+4(α/β)−1+1+γ/δ).

Bottom Line: However, molecular details for the interaction between PUFA and ion channels are not well understood.In this study, we have localized the site of action for PUFAs on the voltage-gated Shaker K channel by introducing positive charges on the channel surface, which potentiated the PUFA effect.Furthermore, we found that PUFA mainly affects the final voltage sensor movement, which is closely linked to channel opening, and that specific charges at the extracellular end of the voltage sensor are critical for the PUFA effect.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Clinical and Experimental Medicine, Division of Cell Biology, Linköping University, Sweden.

ABSTRACT
Free polyunsaturated fatty acids (PUFAs) modulate the voltage dependence of voltage-gated ion channels. As an important consequence thereof, PUFAs can suppress epileptic seizures and cardiac arrhythmia. However, molecular details for the interaction between PUFA and ion channels are not well understood. In this study, we have localized the site of action for PUFAs on the voltage-gated Shaker K channel by introducing positive charges on the channel surface, which potentiated the PUFA effect. Furthermore, we found that PUFA mainly affects the final voltage sensor movement, which is closely linked to channel opening, and that specific charges at the extracellular end of the voltage sensor are critical for the PUFA effect. Because different voltage-gated K channels have different charge profiles, this implies channel-specific PUFA effects. The identified site and the pharmacological mechanism will potentially be very useful in future drug design of small-molecule compounds specifically targeting neuronal and cardiac excitability.

Show MeSH
Related in: MedlinePlus