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Mechanism of inhibition of mouse Slo3 (KCa 5.1) potassium channels by quinine, quinidine and barium.

Wrighton DC, Muench SP, Lippiat JD - Br. J. Pharmacol. (2015)

Bottom Line: The F304Y mutation did not alter the effects of barium, but increased the potency of inhibition by both quinine and quinidine approximately 10-fold; this effect was not observed with the R196Q mutation.Barium inhibits mSlo3 outside the cell by interacting with the selectivity filter, whereas quinine and quinidine act from the inside, by binding in a hydrophobic pocket formed by the S6 segment of each subunit.Furthermore, we propose that the Slo3 channel activation gate lies deep within the pore between F304 in the S6 segment and the selectivity filter.

View Article: PubMed Central - PubMed

Affiliation: School of Biomedical Sciences, Faculty of Biological Sciences, University of Leeds, Leeds, UK.

No MeSH data available.


Related in: MedlinePlus

Concentration-dependent inhibition of WT and F304Y mSlo3 currents by Ba2+. (A) Representative traces recorded before (0) and in the presence of Ba2+ (concentrations in mM as indicated). The dashed line represents the zero-current levels and scale bars represent equivalent current amplitudes and timescales. (B) Mean (± SEM) concentration inhibition plots for WT and F304Y mSlo3 at +100 mV, fitted by the Hill equation provided in the Methods. (C) Apparent voltage-dependence of the IC50 for block by Ba2+ of WT and F304Y mSlo3-mediated currents. The data are described and analysed further in the main text. For key to symbols used see Figure 1.
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fig04: Concentration-dependent inhibition of WT and F304Y mSlo3 currents by Ba2+. (A) Representative traces recorded before (0) and in the presence of Ba2+ (concentrations in mM as indicated). The dashed line represents the zero-current levels and scale bars represent equivalent current amplitudes and timescales. (B) Mean (± SEM) concentration inhibition plots for WT and F304Y mSlo3 at +100 mV, fitted by the Hill equation provided in the Methods. (C) Apparent voltage-dependence of the IC50 for block by Ba2+ of WT and F304Y mSlo3-mediated currents. The data are described and analysed further in the main text. For key to symbols used see Figure 1.

Mentions: To determine if the F304Y mutation had more wide-ranging effects on the structure of the pore we studied inhibition by Ba2+ ions. Concentration–inhibition curves were generated for both WT and F304Y mSlo3 currents evoked by depolarizing steps to +100 mV. Despite the differences in channel activity, the properties of inhibition by Ba2+ were similar. The IC50 was 646 ± 100 μM (n = 6) and 525 ± 97 μM (n = 5), with Hill slopes of 0.88 ± 0.11 and 1.05 ± 0.12 for WT and F304Y mSlo3 respectively (Figure 4A and B). Inhibiting concentrations of Ba2+ also appeared to slow the activation of the currents upon depolarization (Figure 4A). Voltage dependence of Ba2+ inhibition was estimated by measuring the apparent IC50 at different voltages, as before. Inhibition of WT and F304Y mSlo3 by Ba2+ was not significantly different with δ values of 0.20 ± 0.09 and 0.12 ± 0.05 respectively (Figure 4C).


Mechanism of inhibition of mouse Slo3 (KCa 5.1) potassium channels by quinine, quinidine and barium.

Wrighton DC, Muench SP, Lippiat JD - Br. J. Pharmacol. (2015)

Concentration-dependent inhibition of WT and F304Y mSlo3 currents by Ba2+. (A) Representative traces recorded before (0) and in the presence of Ba2+ (concentrations in mM as indicated). The dashed line represents the zero-current levels and scale bars represent equivalent current amplitudes and timescales. (B) Mean (± SEM) concentration inhibition plots for WT and F304Y mSlo3 at +100 mV, fitted by the Hill equation provided in the Methods. (C) Apparent voltage-dependence of the IC50 for block by Ba2+ of WT and F304Y mSlo3-mediated currents. The data are described and analysed further in the main text. For key to symbols used see Figure 1.
© Copyright Policy - open-access
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4556473&req=5

fig04: Concentration-dependent inhibition of WT and F304Y mSlo3 currents by Ba2+. (A) Representative traces recorded before (0) and in the presence of Ba2+ (concentrations in mM as indicated). The dashed line represents the zero-current levels and scale bars represent equivalent current amplitudes and timescales. (B) Mean (± SEM) concentration inhibition plots for WT and F304Y mSlo3 at +100 mV, fitted by the Hill equation provided in the Methods. (C) Apparent voltage-dependence of the IC50 for block by Ba2+ of WT and F304Y mSlo3-mediated currents. The data are described and analysed further in the main text. For key to symbols used see Figure 1.
Mentions: To determine if the F304Y mutation had more wide-ranging effects on the structure of the pore we studied inhibition by Ba2+ ions. Concentration–inhibition curves were generated for both WT and F304Y mSlo3 currents evoked by depolarizing steps to +100 mV. Despite the differences in channel activity, the properties of inhibition by Ba2+ were similar. The IC50 was 646 ± 100 μM (n = 6) and 525 ± 97 μM (n = 5), with Hill slopes of 0.88 ± 0.11 and 1.05 ± 0.12 for WT and F304Y mSlo3 respectively (Figure 4A and B). Inhibiting concentrations of Ba2+ also appeared to slow the activation of the currents upon depolarization (Figure 4A). Voltage dependence of Ba2+ inhibition was estimated by measuring the apparent IC50 at different voltages, as before. Inhibition of WT and F304Y mSlo3 by Ba2+ was not significantly different with δ values of 0.20 ± 0.09 and 0.12 ± 0.05 respectively (Figure 4C).

Bottom Line: The F304Y mutation did not alter the effects of barium, but increased the potency of inhibition by both quinine and quinidine approximately 10-fold; this effect was not observed with the R196Q mutation.Barium inhibits mSlo3 outside the cell by interacting with the selectivity filter, whereas quinine and quinidine act from the inside, by binding in a hydrophobic pocket formed by the S6 segment of each subunit.Furthermore, we propose that the Slo3 channel activation gate lies deep within the pore between F304 in the S6 segment and the selectivity filter.

View Article: PubMed Central - PubMed

Affiliation: School of Biomedical Sciences, Faculty of Biological Sciences, University of Leeds, Leeds, UK.

No MeSH data available.


Related in: MedlinePlus