Abstract 10172: Mitochondrial Connexin43 Can be Involved in the Occurrence of Arrhythmias

Abstract

Background: Connexin43 (Cx43) forms gap junctions in cardiac ventricles and exits as hemichannels in the inner mitochondrial membrane (mCx43). Objective: To examine whether mCx43 is involved in the occurrence of arrhythmias with modulation of mitochondrial K ATP channels (mK ATP ). Methods: To generate cardiac-specific Cx43-deficient ( Cx43 -/- ) mice, Cx43 flox/flox mice were crossed with α-myosin heavy chain -cre +/- mice. The resulting offspring, Cx43 -/- -mice and their littermates ( Cx43 +/+ -mice) were used. Trabeculae were obtained from right ventricles. Force was measured with a strain gauge, Ca 2+ within the mitochondria (Ca m ) with rhod-2, intracellular Ca 2+ (Ca i ) with microinjected fura-2 (22°C). The minimal extracellular Ca 2+ concentration (Cao min ), at which arrhythmias were induced by electrical stimulation, was determined. Using isolated single ventricular myocytes, mitochondrial membrane potential (ΔΨ m ) was estimated with tetramethylrhodamine methylester (TMRM), ROS production with 2’,7’-dichlorofluorescein (DCF), and Ca 2+ spark frequency with fluo-4 and confocal microscopy. Results: Cx43 -/- -mice showed sudden death within 8 weeks (p<0.01). Cx43 was present in the inner mitochondrial membrane in Cx43 +/+ -mice but not in Cx43 -/- -mice. Developed force and Ca i transients by 0.5 Hz electrical stimulation showed no difference between Cx43 -/- - and Cx43 +/+ -mice (n=7). The Cao min in Cx43 -/- -mice was lower than that in Cx43 +/+ -mice (n=5, p<0.01) and was increased by diazoxide (DZX, n=4, p<0.05), suggesting that arrhythmia susceptibility is increased in Cx43 -/- -mice and is suppressed by DZX. Ca 2+ spark frequency and DCF oxidation rate in Cx43 -/- -mice were higher (p<0.01) and were decreased by DZX (p<0.01). TMRM fluorescence was decreased in Cx43 -/- -mice, and it was increased by DZX (p<0.01) and was decreased by 5-hydroxydecanoic acid (p<0.01). Rhod-2 signal was increased at 4 - 6 mM extracellular Ca 2+ in Cx43 -/- -mice but not in Cx43 +/+ -mice. Conclusions: Cx43 deficiency depolarizes ΔΨ m and increases Ca m at higher Ca o , ROS production, Ca 2+ spark frequency, and arrhythmia susceptibility. These changes in Cx43 -/- -mice are suppressed by DZX. Thus, mCx43 can be involved in the occurrence of arrhythmias with modulation of mK ATP .