[en] Small conductance calcium-activated potassium (SK) 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: τ c,vl=11.8±7.1 s, and AP14145: τ c,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: τ c,s=3.50±0.81 ms, and τ c,i=32.0±6.76 ms vs. control: τ c,s=1.59±0.19 ms, and τ c,i=13.5±1.17 ms), thus slowing overall gating kinetics within bursts of channel activity. In contrast, apamin accelerated intra-burst gating kinetics by shortening the two shortest closed durations (τ c,s=0.75±0.10 ms and τ c,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 vs. 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.
Disciplines :
Biochemistry, biophysics & molecular biology
Author, co-author :
van Herck, Ilsbeth G M; Computational Physiology Department, Simula Research Laboratory, Oslo, Norway, Institute of informatics, University of Oslo, Norway
Seutin, Vincent ; Université de Liège - ULiège > Département des sciences biomédicales et précliniques > Pharmacologie
Bentzen, Bo H; Acesion Pharma, Copenhagen, Denmark, Biomedical Institute, University of Copenhagen, Copenhagen, Denmark
Marrion, Neil V; School of Physiology, Pharmacology and Neuroscience, University of Bristol, Bristol, United Kingdom
Edwards, Andrew G ; Computational Physiology Department, Simula Research Laboratory, Oslo, Norway, Department of Pharmacology, University of California, Davis, CA, USA. Electronic address: andy@simula.no
Language :
English
Title :
Gating kinetics and pharmacological properties of small conductance calcium-activated potassium channels.
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