Abstract
The current study explored the Na+/K+-ATPase (NKA) inhibition-independent proarrhythmic mechanisms of cardiac glycosides (CGs) which are well-known NKA inhibitors. With the cytosolic Ca2+ chelated by EGTA and BAPTA or extracellular Ca2+ replaced by Ba2+, effects of bufadienolides (bufalin (BF) and cinobufagin (CBG)) and cardenolides (ouabain (Oua) and pecilocerin A (PEA)) on the L-type calcium current (ICa,L) were recorded in heterologous expression Cav1.2-CHO cells and human embryonic stem cell-derived cardiomyocytes (hESC-CMs). BF and CBG demonstrated a concentration-dependent (0.1 to 100 µM) ICa,L inhibition (maximal ≥50%) without and with the NKA activity blocked by 10 µM Oua. BF significantly shortened the action potential duration at 1.0 µM and shortened the extracellular field potential duration at 0.01~1.0 µM. On the other hand, BF and CBG at 100 µM demonstrated a strong inhibition (≥40%) of the rapidly activating component of the delayed rectifier K+ current (IKr) in heterologous expression HEK293 cells and prolonged the APD of the heart of day-3 Zebrafish larva with disrupted rhythmic contractions. Moreover, hESC-CMs treated with BF (10 nM) for 24 hours showed moderate yet significant prolongation in APD90. In conclusion, our data indicate that CGs particularly bufadienolides possess cytosolic [Ca2+]i- and NKA inhibition- independent proarrhythmic potential through ICa,L and IKr inhibitions.
Highlights
(BF) and cinobufagin (CBG)) and cardenolides (ouabain (Oua) and pecilocerin A (PEA)) on the L-type calcium current (ICa,L) were recorded in heterologous expression Cav1.2-CHO cells and human embryonic stem cell-derived cardiomyocytes
Based on that used in previous in vitro experiments[5,6,7,8,9] and in patients[10], the concentrations of BF, CBG, Oua and PEA adopted in the current study ranged from 0.1 to 100 μM, whereas 0.01~1.0 μM falls in the therapeutic range and 1.0~10 μM overlapped with the cardiotoxicity range
Data from the current study indicate that NKA inhibition-independent ICa,L inhibition could contribute to the greater proarrhythmic effects of BF and CBG compared with Oua and PEA
Summary
(BF) and cinobufagin (CBG)) and cardenolides (ouabain (Oua) and pecilocerin A (PEA)) on the L-type calcium current (ICa,L) were recorded in heterologous expression Cav1.2-CHO cells and human embryonic stem cell-derived cardiomyocytes (hESC-CMs). NKA inhibition causes an accumulation of cytosolic Na+ which in turn activates the reverse-mode of Na+/ Ca2+-exchanger This leads to an increase in cytosolic [Ca2+]i which perturbs the CGs through positive inotropic effect[3,4,5]. CG-induced accumulation of cytosolic [Ca2+]i is known to accelerate [Ca2+]i-dependent inactivation (CDI) of the L-type Calcium channels (LTCC) and lead to the suppression of the LTCC currents (ICa,L)[11, 12], which could be responsible for the shortening of cardiac action potential (AP) duration (APD) in cardiac myocytes of various animal species[11, 13,14,15,16] and the shortening of the cardiac field potential (FP) duration of human induced pluripotent stem cell-derived cardiomyocytes[17]. Chan Su (toad venom) and its key ingredient BF have demonstrated more potent cardiotoxicity over Oua as additional proarrhythmic effects were achieved by Chan Su or BF after the Na+/K+-ATPase activity was fully blocked by Oua[20, 22]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
