TY - JOUR

T1 - Gating kinetics and pharmacological properties of small-conductance Ca2+-activated potassium channels

AU - van Herck, Ilsbeth G.M.

AU - Seutin, Vincent

AU - Bentzen, Bo H.

AU - Marrion, Neil V.

AU - Edwards, Andrew G.

N1 - Funding Information: I.G.M.v.H. and B.H.B. received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement number 675351. V.S. was supported by grant 9.4560.03 from the FNRS (Belgium). N.V.M. has received funding from the British Heart Foundation under agreement number PG/16/37/31974. A.G.E. was supported by the Norwegian Ministry of Research and Education through the SUURPh international doctoral program. B.H.B. is an employee of, and has financial interest in, Acesion Pharma ApS, a developer of SK targeting compounds including AP14145. Funding Information: I.G.M.v.H. and B.H.B. received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement number 675351 . V.S. was supported by grant 9.4560.03 from the FNRS (Belgium). N.V.M. has received funding from the British Heart Foundation under agreement number PG/16/37/31974 . A.G.E. was supported by the Norwegian Ministry of Research and Education through the SUURPh international doctoral program. Publisher Copyright: © 2023 Biophysical Society

PY - 2023/4/4

Y1 - 2023/4/4

N2 - Small-conductance (SK) calcium-activated potassium channels are a promising treatment target in atrial fibrillation. However, the functional properties that differentiate SK inhibitors remain poorly understood. The objective of this study was to determine how two unrelated SK channel inhibitors, apamin and AP14145, impact SK channel function in excised inside-out single-channel recordings. Surprisingly, both apamin and AP14145 exert much of their inhibition by inducing a class of very-long-lived channel closures (apamin: τc,vl = 11.8 ± 7.1 s, and AP14145: τc,vl = 10.3 ± 7.2 s), which were never observed under control conditions. Both inhibitors also induced changes to the three closed and two open durations typical of normal SK channel gating. AP14145 shifted the open duration distribution to favor longer open durations, whereas apamin did not alter open-state kinetics. AP14145 also prolonged the two shortest channel closed durations (AP14145: τc,s = 3.50 ± 0.81 ms, and τc,i = 32.0 ± 6.76 ms versus control: τc,s = 1.59 ± 0.19 ms, and τc,i = 13.5 ± 1.17 ms), thus slowing overall gating kinetics within bursts of channel activity. In contrast, apamin accelerated intraburst gating kinetics by shortening the two shortest closed durations (τc,s = 0.75 ± 0.10 ms and τc,i = 5.08 ± 0.49 ms) and inducing periods of flickery activity. Finally, AP14145 introduced a unique form of inhibition by decreasing unitary current amplitude. SK channels exhibited two clearly distinguishable amplitudes (control: Ahigh = 0.76 ± 0.03 pA, and Alow = 0.54 ± 0.03 pA). AP14145 both reduced the fraction of patches exhibiting the higher amplitude (AP14145: 4/9 patches versus control: 16/16 patches) and reduced the mean low amplitude (0.38 ± 0.03 pA). Here, we have demonstrated that both inhibitors introduce very long channel closures but that each also exhibits unique effects on other components of SK gating kinetics and unitary current. The combination of these effects is likely to be critical for understanding the functional differences of each inhibitor in the context of cyclical Ca2+-dependent channel activation in vivo.

AB - Small-conductance (SK) calcium-activated potassium channels are a promising treatment target in atrial fibrillation. However, the functional properties that differentiate SK inhibitors remain poorly understood. The objective of this study was to determine how two unrelated SK channel inhibitors, apamin and AP14145, impact SK channel function in excised inside-out single-channel recordings. Surprisingly, both apamin and AP14145 exert much of their inhibition by inducing a class of very-long-lived channel closures (apamin: τc,vl = 11.8 ± 7.1 s, and AP14145: τc,vl = 10.3 ± 7.2 s), which were never observed under control conditions. Both inhibitors also induced changes to the three closed and two open durations typical of normal SK channel gating. AP14145 shifted the open duration distribution to favor longer open durations, whereas apamin did not alter open-state kinetics. AP14145 also prolonged the two shortest channel closed durations (AP14145: τc,s = 3.50 ± 0.81 ms, and τc,i = 32.0 ± 6.76 ms versus control: τc,s = 1.59 ± 0.19 ms, and τc,i = 13.5 ± 1.17 ms), thus slowing overall gating kinetics within bursts of channel activity. In contrast, apamin accelerated intraburst gating kinetics by shortening the two shortest closed durations (τc,s = 0.75 ± 0.10 ms and τc,i = 5.08 ± 0.49 ms) and inducing periods of flickery activity. Finally, AP14145 introduced a unique form of inhibition by decreasing unitary current amplitude. SK channels exhibited two clearly distinguishable amplitudes (control: Ahigh = 0.76 ± 0.03 pA, and Alow = 0.54 ± 0.03 pA). AP14145 both reduced the fraction of patches exhibiting the higher amplitude (AP14145: 4/9 patches versus control: 16/16 patches) and reduced the mean low amplitude (0.38 ± 0.03 pA). Here, we have demonstrated that both inhibitors introduce very long channel closures but that each also exhibits unique effects on other components of SK gating kinetics and unitary current. The combination of these effects is likely to be critical for understanding the functional differences of each inhibitor in the context of cyclical Ca2+-dependent channel activation in vivo.

U2 - 10.1016/j.bpj.2023.02.004

DO - 10.1016/j.bpj.2023.02.004

M3 - Journal article

C2 - 36760125

AN - SCOPUS:85149874633

VL - 122

SP - 1143

EP - 1157

JO - Biophysical Society. Annual Meeting. Abstracts

JF - Biophysical Society. Annual Meeting. Abstracts

SN - 0523-6800

IS - 7

ER -