Abstract 1290: Connexin 43 Controls Mitochondrial Respiration
The preservation of mitochondrial function and integrity is central for cell survival following ischemia/reperfusion. Connexin 43 (Cx43) is the major protein of ventricular gap junctions, but is also present in left ventricular (LV) mitochondria. A reduction in Cx43 protein is associated with loss of diazoxide-induced reactive oxygen species formation and cardioprotection by ischemic preconditioning. However, the exact function of Cx43 within mitochondria is unclear. In our study we analyzed the effect of Cx43 on mitochondrial respiration in two different settings: 1) a reduction and 2) an increase of mitochondrial Cx43 content. Mitochondria were isolated from the LV of wildtype (Cx43+/+, 100% total Cx43) and heterozygous Cx43-deficient mice (Cx43+/−, 50% Cx43), as well as from mice, in which the ablation of Cx43 was induced by the injection of 4-hydroxytamoxifen (Cx43Cre-ER(T)/fl + 4-OHT, 5–10% Cx43) and the respective control strain (Cx43fl/fl, 100% Cx43). Mitochondrial oxygen consumption was measured under baseline conditions and after the addition of ADP. The respiratory control index (RCI: ADP-stimulated respiration/basal respiration) was 3.9±0.6 (n=6) in Cx43+/+ mitochon-dria, and was found to be reduced in mitochondria from Cx43+/− mice (RCI: 3.2±0.4, n=8, p<0.05). The 4-OHT-induced ablation of Cx43 also resulted in a significant decrease in ADP-stimulated oxygen consumption compared to control mitochondria (Cx43fl/f: RCI = 2.8±0.2, n=13 vs. Cx43Cre-ER(T)/fl + 4-OHT: RCI = 2.3±0.1, n=6, p<0.05). HL-1 cardiomy-ocytes were stably transfected with a retrovirus containing the coding sequence of rat Cx43, resulting in an about 2fold overexpression of Cx43 in mitochondria, or with the empty vector. Mitochondria isolated from the Cx43-overexpressing cells had a higher RCI compared to mitochondria from control transfected cells (4.2±0.9, n=5, vs. 2.8±0.2, n=3, p=0.09). In conclusion, oxygen consumption is affected by the mitochondrial content of Cx43. A 50% reduction of total Cx43 is sufficient to decrease and a twofold overexpression of Cx43 to increase respiratory control.