TY - JOUR

T1 - Enhanced Ca2+-Dependent SK-Channel Gating and Membrane Trafficking in Human Atrial Fibrillation

AU - Heijman, Jordi

AU - Zhou, Xiaobo

AU - Morotti, Stefano

AU - Molina, Cristina E.

AU - Abu-Taha, Issam H.

AU - Tekook, Marcel

AU - Jespersen, Thomas

AU - Zhang, Yiqiao

AU - Dobrev, Shokoufeh

AU - Milting, Hendrik

AU - Gummert, Jan

AU - Karck, Matthias

AU - Kamler, Markus

AU - El-Armouche, Ali

AU - Saljic, Arnela

AU - Grandi, Eleonora

AU - Nattel, Stanley

AU - Dobrev, Dobromir

N1 - Publisher Copyright: © 2023 Lippincott Williams and Wilkins. All rights reserved.

PY - 2023

Y1 - 2023

N2 - Background: Small-conductance Ca2+-activated K+(SK)-channel inhibitors have antiarrhythmic effects in animal models of atrial fibrillation (AF), presenting a potential novel antiarrhythmic option. However, the regulation of SK-channels in human atrial cardiomyocytes and its modification in patients with AF are poorly understood and were the object of this study. Methods: Apamin-sensitive SK-channel current (ISK) and action potentials were recorded in human right-atrial cardiomyocytes from sinus rhythm control (Ctl) patients or patients with (long-standing persistent) chronic AF (cAF). Results: ISKwas significantly higher, and apamin caused larger action potential prolongation in cAF- versus Ctl-cardiomyocytes. Sensitivity analyses in an in silico human atrial cardiomyocyte model identified IK1and ISKas major regulators of repolarization. Increased ISKin cAF was not associated with increases in mRNA/protein levels of SK-channel subunits in either right- or left-atrial tissue homogenates or right-atrial cardiomyocytes, but the abundance of SK2 at the sarcolemma was larger in cAF versus Ctl in both tissue-slices and cardiomyocytes. Latrunculin-A and primaquine (anterograde and retrograde protein-trafficking inhibitors) eliminated the differences in SK2 membrane levels and ISKbetween Ctl- and cAF-cardiomyocytes. In addition, the phosphatase-inhibitor okadaic acid reduced ISKamplitude and abolished the difference between Ctl- and cAF-cardiomyocytes, indicating that reduced calmodulin-Thr80 phosphorylation due to increased protein phosphatase-2A levels in the SK-channel complex likely contribute to the greater ISKin cAF-cardiomyocytes. Finally, rapid electrical activation (5 Hz, 10 minutes) of Ctl-cardiomyocytes promoted SK2 membrane-localization, increased ISKand reduced action potential duration, effects greatly attenuated by apamin. Latrunculin-A or primaquine prevented the 5-Hz-induced ISK-upregulation. Conclusions: ISKis upregulated in patients with cAF due to enhanced channel function, mediated by phosphatase-2A-dependent calmodulin-Thr80 dephosphorylation and tachycardia-dependent enhanced trafficking and targeting of SK-channel subunits to the sarcolemma. The observed AF-associated increases in ISK, which promote reentry-stabilizing action potential duration shortening, suggest an important role for SK-channels in AF auto-promotion and provide a rationale for pursuing the antiarrhythmic effects of SK-channel inhibition in humans.

AB - Background: Small-conductance Ca2+-activated K+(SK)-channel inhibitors have antiarrhythmic effects in animal models of atrial fibrillation (AF), presenting a potential novel antiarrhythmic option. However, the regulation of SK-channels in human atrial cardiomyocytes and its modification in patients with AF are poorly understood and were the object of this study. Methods: Apamin-sensitive SK-channel current (ISK) and action potentials were recorded in human right-atrial cardiomyocytes from sinus rhythm control (Ctl) patients or patients with (long-standing persistent) chronic AF (cAF). Results: ISKwas significantly higher, and apamin caused larger action potential prolongation in cAF- versus Ctl-cardiomyocytes. Sensitivity analyses in an in silico human atrial cardiomyocyte model identified IK1and ISKas major regulators of repolarization. Increased ISKin cAF was not associated with increases in mRNA/protein levels of SK-channel subunits in either right- or left-atrial tissue homogenates or right-atrial cardiomyocytes, but the abundance of SK2 at the sarcolemma was larger in cAF versus Ctl in both tissue-slices and cardiomyocytes. Latrunculin-A and primaquine (anterograde and retrograde protein-trafficking inhibitors) eliminated the differences in SK2 membrane levels and ISKbetween Ctl- and cAF-cardiomyocytes. In addition, the phosphatase-inhibitor okadaic acid reduced ISKamplitude and abolished the difference between Ctl- and cAF-cardiomyocytes, indicating that reduced calmodulin-Thr80 phosphorylation due to increased protein phosphatase-2A levels in the SK-channel complex likely contribute to the greater ISKin cAF-cardiomyocytes. Finally, rapid electrical activation (5 Hz, 10 minutes) of Ctl-cardiomyocytes promoted SK2 membrane-localization, increased ISKand reduced action potential duration, effects greatly attenuated by apamin. Latrunculin-A or primaquine prevented the 5-Hz-induced ISK-upregulation. Conclusions: ISKis upregulated in patients with cAF due to enhanced channel function, mediated by phosphatase-2A-dependent calmodulin-Thr80 dephosphorylation and tachycardia-dependent enhanced trafficking and targeting of SK-channel subunits to the sarcolemma. The observed AF-associated increases in ISK, which promote reentry-stabilizing action potential duration shortening, suggest an important role for SK-channels in AF auto-promotion and provide a rationale for pursuing the antiarrhythmic effects of SK-channel inhibition in humans.

KW - actinin

KW - apamin

KW - atrial fibrillation

KW - atrial remodeling

KW - calmodulin

KW - protein phosphatase-2A

KW - protein transport

UR - http://www.scopus.com/inward/record.url?scp=85158020207&partnerID=8YFLogxK

U2 - 10.1161/CIRCRESAHA.122.321858

DO - 10.1161/CIRCRESAHA.122.321858

M3 - Journal article

C2 - 36927079

AN - SCOPUS:85158020207

VL - 132

SP - E116-E133

JO - Circulation Research

JF - Circulation Research

SN - 0009-7330

IS - 9

ER -