B-PO02-019 MITOCHONDRIAL CONNEXIN43 IS INVOLVED IN THE OCCURRENCE OF ARRHYTHMIAS WITH MODULATION OF MITOCHONDRIAL KATP CHANNELS

Abstract

Connexin43 (Cx43) forms gap junctional channels in cardiac ventricles and exits as hemichannels in the inner mitochondrial membrane (mCx43). To examine whether mCx43 and mitochondrial KATP channels (mKATP) affect the occurrence of arrhythmias. To generate cardiac-specific Cx43-deficient (Cx43-/-) mice, Cx43flox/flox mice were crossed with α-myosin heavy chain (Myh6)-cre+/- mice. The resulting offspring, Cx43-/--mice and their littermates (Cx43+/+-mice) were used. Trabeculae were dissected from ventricles. Force was measured with a silicon strain gauge, Ca2+ within the mitochondria (Cam) with rhod-2, intracellular Ca2+ (Cai) with microinjected fura-2 (22°C). The minimal extracellular Ca2+ concentration (Caomin), at which arrhythmias were induced by electrical stimulation, was determined. Using isolated single ventricular myocytes, mitochondrial membrane potential (ΔΨm) was estimated with tetramethylrhodamine methylester (TMRM), ROS production with 2’,7’-dichlorofluorescein (DCF), and Ca2+ spark frequency with fluo-4 and confocal microscopy. Most of Cx43-/--mice died 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 Cai transients by 0.5 Hz electrical stimulation showed no difference between Cx43-/-- and Cx43+/+-mice (n=7). The Caomin 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 arrhythmogenesis is increased in Cx43-/--mice and is suppressed by DZX. Ca2+ 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 after 1 Hz stimulation 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 in Cx43-/--mice but not in Cx43+/+-mice at 4 - 6 mM extracellular Ca2+ (Cao). Cx43 deficiency depolarizes ΔΨm and increases Cam at higher Cao, ROS production, Ca2+ spark frequency, and arrhythmogenesis. All these changes in Cx43-/--mice are suppressed by DZX. Thus, with modulation of mKATP, mCx43 can be involved in the occurrence of arrhythmias.