BACKGROUND: Activation of small conductance calcium-activated potassium (SK) channels is proposed to contribute to repolarization of the action potential in atrial myocytes. This role is controversial, as these cardiac SK channels appear to exhibit an uncharacteristic pharmacology. OBJECTIVES: The objectives of this study were to resolve whether activation of SK channels contributes to atrial action potential repolarization and to determine the likely subunit composition of the channel. METHODS: The effect of 2 SK channel inhibitors was assessed on outward current evoked in voltage clamp and on action potential duration in perforated patch and whole-cell current clamp recording from acutely isolated mouse atrial myocytes. The presence of SK channel subunits was assessed using immunocytochemistry. RESULTS: A significant component of outward current was reduced by the SK channel blockers apamin and UCL1684. Block by apamin displayed a sensitivity indicating that this current was carried by homomeric SK2 channels. Action potential duration was significantly prolonged by UCL1684, but not by apamin. This effect was accompanied by an increase in beat-to-beat variability and action potential triangulation. This pharmacology was matched by that of expressed heteromeric SK2-SK3 channels in HEK293 cells. Immunocytochemistry showed that atrial myocytes express both SK2 and SK3 channels with an overlapping expression pattern. CONCLUSION: Only proposed heteromeric SK2-SK3 channels are physiologically activated to contribute to action potential repolarization, which is indicated by the difference in pharmacology of evoked outward current and prolongation of atrial action potential duration. The effect of blocking this channel on the action potential suggests that SK channel inhibition during cardiac function has the potential to be proarrhythmic.
BACKGROUND: Activation of small conductance calcium-activated potassium (SK) channels is proposed to contribute to repolarization of the action potential in atrial myocytes. This role is controversial, as these cardiac SK channels appear to exhibit an uncharacteristic pharmacology. OBJECTIVES: The objectives of this study were to resolve whether activation of SK channels contributes to atrial action potential repolarization and to determine the likely subunit composition of the channel. METHODS: The effect of 2 SK channel inhibitors was assessed on outward current evoked in voltage clamp and on action potential duration in perforated patch and whole-cell current clamp recording from acutely isolated mouse atrial myocytes. The presence of SK channel subunits was assessed using immunocytochemistry. RESULTS: A significant component of outward current was reduced by the SK channel blockers apamin and UCL1684. Block by apamin displayed a sensitivity indicating that this current was carried by homomeric SK2 channels. Action potential duration was significantly prolonged by UCL1684, but not by apamin. This effect was accompanied by an increase in beat-to-beat variability and action potential triangulation. This pharmacology was matched by that of expressed heteromeric SK2-SK3 channels in HEK293 cells. Immunocytochemistry showed that atrial myocytes express both SK2 and SK3 channels with an overlapping expression pattern. CONCLUSION: Only proposed heteromeric SK2-SK3 channels are physiologically activated to contribute to action potential repolarization, which is indicated by the difference in pharmacology of evoked outward current and prolongation of atrial action potential duration. The effect of blocking this channel on the action potential suggests that SK channel inhibition during cardiac function has the potential to be proarrhythmic.
Authors: Mu Chen; Dong-Zhu Xu; Adonis Z Wu; Shuai Guo; Juyi Wan; Dechun Yin; Shien-Fong Lin; Zhenhui Chen; Michael Rubart-von der Lohe; Thomas H Everett; Zhilin Qu; James N Weiss; Peng-Sheng Chen Journal: JCI Insight Date: 2018-11-15
Authors: Jum-Suk Ko; Shuai Guo; Jonathan Hassel; Patricia Celestino-Soper; Ty C Lynnes; James E Tisdale; James J Zheng; Stanley E Taylor; Tatiana Foroud; Michael D Murray; Richard J Kovacs; Xiaochun Li; Shien-Fong Lin; Zhenhui Chen; Matteo Vatta; Peng-Sheng Chen; Michael Rubart Journal: Am J Physiol Heart Circ Physiol Date: 2018-04-20 Impact factor: 4.733
Authors: Tesfaye Negash Asfaw; Leonid Tyan; Alexey V Glukhov; Vladimir E Bondarenko Journal: Am J Physiol Heart Circ Physiol Date: 2020-01-17 Impact factor: 4.733
Authors: Bruno Bragança; Nádia Oliveira-Monteiro; Fátima Ferreirinha; Pedro A Lima; Miguel Faria; Ana P Fontes-Sousa; Paulo Correia-de-Sá Journal: Front Pharmacol Date: 2016-03-07 Impact factor: 5.810