title: SK4 Ca2+ activated K+ channel is a critical player in cardiac pacemaker derived from human embryonic stem cells.
abstract: Proper expression and function of the cardiac pacemaker is a critical feature of heart physiology. Two main mechanisms have been proposed: (i) the "voltage-clock," where the hyperpolarization-activated funny current If causes diastolic depolarization that triggers action potential cycling; and (ii) the "Ca(2+) clock," where cyclical release of Ca(2+) from Ca(2+) stores depolarizes the membrane during diastole via activation of the Na(+)-Ca(2+) exchanger. Nonetheless, these mechanisms remain controversial. Here, we used human embryonic stem cell-derived cardiomyocytes (hESC-CMs) to study their autonomous beating mechanisms. Combined current- and voltage-clamp recordings from the same cell showed the so-called "voltage and Ca(2+) clock" pacemaker mechanisms to operate in a mutually exclusive fashion in different cell populations, but also to coexist in other cells. Blocking the "voltage or Ca(2+) clock" produced a similar depolarization of the maximal diastolic potential (MDP) that culminated by cessation of action potentials, suggesting that they converge to a common pacemaker component. Using patch-clamp recording, real-time PCR, Western blotting, and immunocytochemistry, we identified a previously unrecognized Ca(2+)-activated intermediate K(+) conductance (IK(Ca), KCa3.1, or SK4) in young and old stage-derived hESC-CMs. IK(Ca) inhibition produced MDP depolarization and pacemaker suppression. By shaping the MDP driving force and exquisitely balancing inward currents during diastolic depolarization, IK(Ca) appears to play a crucial role in human embryonic cardiac automaticity.
authors.affiliation: Department of Physiology and Pharmacology, The Sackler Faculty of Medicine, Tel Aviv University, Ramat Aviv 69978, Israel.
authors.forename: David
authors.initials: D
authors.lastname: Weisbrod
authors.forename: Asher
authors.initials: A
authors.lastname: Peretz
authors.forename: Anna
authors.initials: A
authors.lastname: Ziskind
authors.forename: Nataly
authors.initials: N
authors.lastname: Menaker
authors.forename: Shimrit
authors.initials: S
authors.lastname: Oz
authors.forename: Lili
authors.initials: L
authors.lastname: Barad
authors.forename: Sivan
authors.initials: S
authors.lastname: Eliyahu
authors.forename: Joseph
authors.initials: J
authors.lastname: Itskovitz-Eldor
authors.forename: Nathan
authors.initials: N
authors.lastname: Dascal
authors.forename: Daniel
authors.initials: D
authors.lastname: Khananshvili
authors.forename: Ofer
authors.initials: O
authors.lastname: Binah
authors.forename: Bernard
authors.initials: B
authors.lastname: Attali
mesh_terms: D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D002460:Cell Line; D053595:Embryonic Stem Cells / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D051660:Intermediate-Conductance Calcium-Activated Potassium Channels / Q000378:metabolism*; D008955:Models, Cardiovascular; D032383:Myocytes, Cardiac / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D011720:Pyrazoles / Q000494:pharmacology; D011743:Pyrimidines / Q000494:pharmacology; D019837:Ryanodine Receptor Calcium Release Channel / Q000378:metabolism; D012849:Sinoatrial Node / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism*; D013890:Thiourea / Q000031:analogs & derivatives / Q000494:pharmacology
chemical_list: C101670:2-(2-(4-(4-nitrobenzyloxy)phenyl)ethyl)isothiourea methanesulfonate; D051660:Intermediate-Conductance Calcium-Activated Potassium Channels; C496923:KCNN4 protein, human; D011720:Pyrazoles; D011743:Pyrimidines; D019837:Ryanodine Receptor Calcium Release Channel; C411671:TRAM 34; C082246:ICI D2788; D013890:Thiourea