Respiration of permeabilized cardiomyocytes from mice: no sex differences, but substrate-dependent changes in the apparent ADP-affinity
Niina Karro, Martin Laasmaa, Marko Vendelin, Rikke Birkedal
Sci Rep, 2019 Aug 29; 9(1): 12592.
- PMID: 31467353
- DOI: 10.1038/s41598-019-48964-x
Significance
Male and female hearts can differ in health and disease, but it is unclear whether their individual heart cells have different energy-producing capacity. This published paper measured respiration in permeabilized mouse cardiomyocytes and found no sex differences in mitochondrial content, respiratory capacity, or the apparent ability of ADP to reach mitochondria. Instead, the metabolic substrates supplied to the cells changed their apparent ADP affinity. The results show that fuel choice can influence internal barriers to energy transfer in heart cells, an important consideration for studies of cardiac metabolism.
Abstract
Sex differences in cardiac physiology are getting increased attention. This study assessed whether isolated, permeabilized cardiomyocytes from male and female C57BL/6 mice differ in terms of their respiration with multiple substrates and overall intracellular diffusion restriction estimated by the apparent ADP-affinity of respiration. Using respirometry, we recorded 1) the activities of respiratory complexes I, II and IV, 2) the respiration rate with substrates fuelling either complex I, II, or I + II, and 3) the apparent ADP-affinity with substrates fuelling complex I and I + II. The respiration rates were normalized to protein content and citrate synthase (CS) activity. We found no sex differences in CS activity (a marker of mitochondrial content) normalized to protein content or in any of the respiration measurements. This suggests that cardiomyocytes from male and female mice do not differ in terms of mitochondrial respiratory capacity and apparent ADP-affinity. Pyruvate modestly lowered the respiration rate, when added to succinate, glutamate and malate. This may be explained by intramitochondrial compartmentalization caused by the formation of supercomplexes and their association with specific dehydrogenases. To our knowledge, we show for the first time that the apparent ADP-affinity was substrate-dependent. This suggests that substrates may change or regulate intracellular barriers in cardiomyocytes.