Substrate‐Dependent Differential Regulation of Mitochondrial Bioenergetics and ROS emission in the Heart and Kidney Cortex and Outer Medulla

Abstract

RationaleThe kinetics and efficiency of mitochondrial oxidative phosphorylation (OxPhos) is determined by the availability and utilization of particular respiratory substrates. Although the heart and kidney represent the two major energy consuming organs in the body, the substrate dependency of their mitochondrial OxPhos has not been characterized for these two organs within the same species and same individual animal.MethodThe effects of different substrate combinations on the kinetics and efficiency of OxPhos were characterized in mitochondria isolated from the heart, renal cortex, and renal outer medulla (OM) of adult Sprague‐Dawley rats. The substrate combinations included pyruvate+malate (PM), glutamate+malate (GM), palmitoyl‐carnitine+malate (PCM), alpha‐ketoglutarate+malate (AM), and succinate±rotenone (Suc±Rot). Mitochondrial bioenergetics (O2 consumption and membrane potential) and H2O2 emission were studied using two protocols: addition of a fixed [ADP] and sequential additions of incremental [ADP] in the presence of different substrates to determine how these substrates influence mitochondrial functional markers in each of these tissues.ResultsResults show that the kinetics and efficiency of mitochondrial OxPhos are highly dependent on the substrates used and this dependency is tissue‐specific. Heart mitochondria showed higher respiratory rates and OxPhos efficiencies for all substrates used in comparison to kidney mitochondria. Renal cortex mitochondrial respiratory rates were higher than OM mitochondria, but OM mitochondria OxPhos efficiencies were higher than cortex mitochondria. It was also found that heart mitochondria do not synthesize ATP efficiently from ADP with Suc in the absence of Rot (blocker of complex I). This may be due to (i) accumulation of oxaloacetate (OAA) and/or (ii) occurrence of reverse electron transfer (RET). In contrast, cortex and OM mitochondria achieved the same respiratory rates with Suc±Rot suggesting that efficient conversion of ADP to ATP by kidney mitochondria can occur in the presence of Suc. Similar differences were observed in mitochondrial membrane potential. However, differences in H2O2 emission in the presence of Suc±Rot were observed in heart mitochondria and to a lesser extent in OM mitochondria, but not in cortex mitochondria. The bioenergetics and H2O2 emission data observed with Suc±Rot indicate that OAA accumulation and RET play a more prominent regulatory role in heart mitochondria than in kidney mitochondria.ConclusionThis study provided novel quantitative data demonstrating that the choice of respiratory substrates affects mitochondrial bioenergetics and H2O2 emission in a tissue‐specific manner.