Park, Song-Young2; Gifford, Jayson R7; Andtbacka, Robert H I4; Hyngstrom, John R7; Garten, Ryan S5; Diakos, Nikolaos A6; Ives, Stephen J7; Dela, Flemming8; Larsen, Steen8; Drakos, Stavros7; Richardson, Russell S7
1 Section of Systems Biology Research, Department of Biomedical Sciences, Faculty of Health and Medical Sciences, Københavns Universitet2 unknown3 University of Utah4 Huntsman Cancer Hospital.5 George E Whalen Veterans Affairs Medical Center.6 National & Kapodestrian University of Athens.7 University of Utah8 Section of Systems Biology Research, Department of Biomedical Sciences, Faculty of Health and Medical Sciences, Københavns Universitet
Are all mitochondria created equal?
Unlike cardiac and skeletal muscle, little is known about vascular smooth muscle mitochondrial function. Therefore, this study examined mitochondrial respiratory rates in the smooth muscle of healthy human feed arteries and compared with that of healthy cardiac and skeletal muscle. Cardiac, skeletal, and smooth muscle was harvested from a total of 22 subjects (53±6 yrs) and mitochondrial respiration assessed in permeabilized fibers. Complex I+II, state 3 respiration, an index of oxidative phosphorylation capacity, fell progressively from cardiac, skeletal, to smooth muscle (54±1; 39±4; 15±1 pmol•s(-1)•mg (-1), p<0.05, respectively). Citrate synthase (CS) activity, an index of mitochondrial density, also fell progressively from cardiac, skeletal, to smooth muscle (222±13; 115±2; 48±2 umol•g(-1)•min(-1), p<0.05, respectively). Thus, when respiration rates were normalized by CS (respiration per mitochondrial content), oxidative phosphorylation capacity was no longer different between the three muscle types. Interestingly, Complex I state 2 normalized for CS activity, an index of non-phosphorylating respiration per mitochondrial content, increased progressively from cardiac, skeletal, to smooth muscle, such that the respiratory control ratio (RCR), state 3/state 2 respiration, fell progressively from cardiac, skeletal, to smooth muscle (5.3±0.7; 3.2±0.4; 1.6±0.3, pmol•s(-1)•mg (-1) p<0.05, respectively). Thus, although oxidative phosphorylation capacity per mitochondrial content in cardiac, skeletal, and smooth muscle suggest all mitochondria are created equal, the contrasting RCR and non-phosphorylating respiration highlight the existence of intrinsic functional differences between these muscle mitochondria. This likely influences the efficiency of oxidative phosphorylation and could potentially ROS production.
American Journal of Physiology: Heart and Circulatory Physiology, 2014, Vol 307, Issue 3