Avian mitochondria respiration is not predicated solely on complex abundance and DNA content

Skeletal muscle is a collection of heterogenous muscle fiber types differing in their ability to contract and metabolize energy substrates. The relative proportion of each fiber type in muscle drive function, where oxidative muscles are more fatigue resistant and generally have greater amounts of mitochondria than more glycolytic muscles that have less mitochondria because of their reliance on glycolytic reactions for energy production. However, even highly glycolytic muscles, like the breast muscle of chickens have mitochondria. Yet, differences in mitochondrial characteristics across muscle types remain largely unknown.We compared glycolytic and oxidative muscles of two different species in an attempt to understand better the relationship between mitochondrial DNA (mtDNA) and protein abundance, and mitochondria function. Glycolytic muscles longissimus lumborum (LL) and the pectoralis major (PM) and oxidative muscles masseter (MS) and quadriceps femoris (QF) were collected from adult pigs and chickens, respectively. Greater mtDNA abundance (2 -ΔΔCT ) was noted in oxidative muscles of both species compared to their glycolytic counterparts ( P < 0.01). However, when absolute mtDNA was estimated, porcine MS had more mtDNA than LL ( P < 0.001), whereas both avian muscles were equivalent. Porcine MS muscle had greater succinate dehydrogenase (SDHA, P < 0.05) and citrate synthase (CS, P < 0.001) than LL, while avian QF muscle had greater CS ( P < 0.001) and voltage dependent anion channel (VDAC, P < 0.05) compared to PM muscle. Isolated mitochondria from the MS of pigs had more electron transport chain complex I (CI, P < 0.010) and complex II (CII, P < 0.05) than those isolated from the LL. Avian mitochondria had no differences in either electron transport chain complexes across muscle, but mitochondria from the PM had greater VDAC than those purified from the QF. Oxygen consumption rates (OCR) followed muscle type, where mitochondria from oxidative muscles consumed more oxygen than those of glycolytic muscle when stimulated with ADP ( P < 0.05). These data show that porcine mtDNA abundance, mitochondrial protein abundance, and mitochondrial function is greater in oxidative muscle compared to glycolytic muscle, and that respiration is greater in mitochondria from more oxidative muscle. However, differences in the relative abundance of mtDNA and electron transport chain complexes were not evident in isolated mitochondria from the chicken, yet respired differently nonetheless suggesting mtDNA and protein may not be directly correlated to the overall function of mitochondria. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.