Mitochondrial connexin 43 impacts on respiratory complex I activity and mitochondrial oxygen consumption

Abstract

Connexin 43 (Cx43) is present at the sarcolemma and the inner membrane of cardiomyocyte subsarcolemmal mitochondria (SSM). Lack or inhibition of mitochondrial Cx43 is associated with reduced mitochondrial potassium influx, which might affect mitochondrial respiration. Therefore, we analysed the importance of mitochondrial Cx43 for oxygen consumption. Acute inhibition of Cx43 in rat left ventricular (LV) SSM by 18α glycyrrhetinic acid (GA) or Cx43 mimetic peptides (Cx43-MP) reduced ADP-stimulated complex I respiration and ATP generation. Chronic reduction of Cx43 in conditional knockout mice (Cx43Cre-ER(T)/fl + 4-OHT, 5–10% of Cx43 protein compared with control Cx43fl/fl mitochondria) reduced ADP-stimulated complex I respiration of LV SSM to 47.8 ± 2.4 nmol O2/min.*mg protein (n = 8) from 61.9 ± 7.4 nmol O2/min.*mg protein in Cx43fl/fl mitochondria (n = 10, P < 0.05), while complex II respiration remained unchanged. The LV complex I activities (% of citrate synthase activity) of Cx43Cre-ER(T)/fl+4-OHT mice (16.1 ± 0.9%, n = 9) were lower than in Cx43fl/fl mice (19.8 ± 1.3%, n = 8, P < 0.05); complex II activities were similar between genotypes. Supporting the importance of Cx43 for respiration, in Cx43-overexpressing HL-1 cardiomyocytes complex I respiration was increased, whereas complex II respiration remained unaffected. Taken together, mitochondrial Cx43 is required for optimal complex I activity and respiration and thus mitochondrial ATP-production.

Strategic Positioning and Biased Activity of the Mitochondrial Calcium Uniporter in Cardiac Muscle

“…Absorbance at 405 nm was tracked for 5 min (10-s intervals). Enzyme activity was expressed as citrate synthase activity units per mg of mitochondrial protein (28). The mitochondrial inner membrane intactness was calculated as the ratio between the citrate synthase activity of the mitochondria preparation in Tris-HCl buffer (0.1 M, pH 8) versus the activity of the same mitochondria preparation treated with 0.1% Triton X-100 lysis buffer (giving the percentage of "leaky" or broken mitochondria).…”

Interaction of Risk Factors, Comorbidities, and Comedications with Ischemia/Reperfusion Injury and Cardioprotection by Preconditioning, Postconditioning, and Remote Conditioning

“…Cx43 is believed to form hemichannels in the inner mitochondrial membrane, thereby facilitating complex I function and the influx of K + into mitochondria in response to the ischemic preconditioning stimulus (Boengler et al, 2012(Boengler et al, , 2013aSoetkamp et al, 2014). The activation of the RISK or SAFE pathways is not involved in the protective function of Cx43 in ischemic preconditioning (Sanchez et al, 2013).…”

Molecular Basis of Cardioprotection

“…360,361 Activation of mitochondrial Cx 43 channels contributes to mitochondrial potassium uptake, 362,363 increases respiration at complex I and mitochondrial oxygen consumption and ATP formation, 364 and in close interaction with mitochondrial K ATP -channels releases ROS. 365 Cx 43 is expressed in subsarcolemmal mitochondria, presumably serving a signaling function, but not in interfibrillar mitochondria.…”