Abstract 14187: Blockade of Connexin43 by Carbenoxolone Increases Arrhythmias under Modulation of Mitochondrial KATP Channels
Connexin43 (Cx43) forms gap junction (GJ) channels in the heart and is also present in the inner mitochondrial membrane. The presence of Cx43 is needed for cardioprotection by pharmacological preconditioning with diazoxide, a mitochondrial KATP (mKATP) channel opener. Using carbenoxolone (CBX), a blocker of Cx43, we examined how the blockade of Cx43 and the modulation of mKATP channels affect Ca2+ waves and triggered arrhythmias in the myocardium with nonuniform contraction.
Methods: Trabeculae were obtained from rat hearts. Force and intracellular Ca2+ were measured. The permeability of GJs (PGJ) was calculated from the diffusion coefficients for fura-2. Nonuniform contraction was created by a jet of 20 mM 2,3-butanedione monoxime solution. Ca2+ waves were induced by 2.5 Hz electrical stimulation for 7.5 s. Inducibility of arrhythmias was estimated from the minimal [Ca2+]o at which arrhythmias were induced by electrical stimulation. The mitochondrial membrane potential (ΔΨm) was assessed using tetramethylrhodamine methylester (TMRM) fluorescence. The Ca2+ spark rate was measured in isolated single rat ventricular myocytes using fluo-4 and fast 2D confocal microscopy.
Results: CBX (5 μM) decreased the PGJ (p<0.01, n=7), whereas it increased the amplitude of aftercontractions (p<0.01) and the propagation velocity of Ca2+ waves after electrical stimulation (p<0.01, n=11). CBX increased the Ca2+ leak from the sarcoplasmic reticulum in trabeculae (p<0.05, n=7) and the Ca2+ spark rate in isolated single myocytes (p<0.05) and further increased the inducibility of arrhythmias (p<0.05, n=6). CBX increased the inducibility of arrhythmias in the presence of 5-hydroxydecanoic acid, a mKATP channel blocker (p<0.05, n=4), but not in the presence of diazoxide nor cromakalim (n=7). CBX decreased TMRM fluorescence, and this decrease was suppressed by diazoxide.
Conclusions: CBX depolarized ΔΨm and increased the inducibility of arrhythmias, and activation of mKATP channels suppressed these changes, suggesting that arrhythmias are increased when both Cx43 and mKATP channels are closed in the myocardium with nonuniform contraction. Thus, in diseased hearts Cx43 is deeply involved with the occurrence of arrhythmias under the modulation of mKATP channels.
Author Disclosures: M. Miura: None. T. Handoh: None. T. Hasegawa: None. R. Ozawa: None. C. Shindoh: None.
- © 2016 by American Heart Association, Inc.