Impaired ATP turnover and ADP supply depress cardiac mitochondrial respiration and elevate superoxide in nonfailing spontaneously hypertensive rat hearts

Abstract

Hickey AJ, Chai CC, Choong SY, de Freitas Costa S, Skea GL, Phillips AR, Cooper GJ. Impaired ATP turnover and ADP supply depress cardiac mitochondrial respiration and elevate superoxide in nonfailing spontaneously hypertensive rat hearts. Am J Physiol Cell Physiol 297: C766 -C774, 2009. First published June 24, 2009 doi:10.1152/ajpcell.00111.2009.-Although most attention has been focused on mitochondrial ATP production and transfer in failing hearts, less has been focused on the nonfailing hypertensive heart. Here, energetic complications are less obvious, yet they may provide insight into disease ontogeny. We studied hearts from 12-mo-old spontaneously hypertensive rats (SHR) relative to normotensive Wistar-Kyoto (WKY) rats. The ex vivo working-heart model of SHR showed reduced compliance and impaired responses to increasing preloads. High-resolution respirometry showed higher state 3 (with excess ADP) respiration in SHR left ventricle fibers with complex I substrates and maximal uncoupled respiration with complex I ϩ complex II substrates. Respiration with ATP was depressed 15% in SHR fibers relative to WKY fibers, suggesting impaired ATP hydrolysis. This finding was consistent with a 50% depression of actomyosin ATPase activities. Superoxide production from SHR fibers was similar to that from WKY fibers respiring with ADP; however, it was increased by 15% with ATP. In addition, the apparent Km for ADP was 54% higher for SHR fibers, and assays conducted after ex vivo work showed a 28% depression of complex I in SHR, but not WKY, fibers. Transmission electron microscopy showed similar mitochondrial volumes but a decrease in the number of cristae in SHR mitochondria. Tissue lipid peroxidation was also 15% greater in SHR left ventricle. Overall, these data suggest that although cardiac mitochondria from nonfailing SHR hearts function marginally better than those from WKY hearts, they show dysfunction after intense work. Impaired ATP turnover in hard-working SHR hearts may starve cardiac mitochondria of ADP and elevate superoxide. adenylate control; saponin-permeabilized fibers; hypertensive heart; oxidative stress; complex I dysfunction; respiration MITOCHONDRIAL ENERGY PRODUCTION and linked energy transfer to ATP-consuming processes are central to the maintenance of physiological cell and tissue functions. Cardiac mitochondria occupy 30 -40% of the healthy mammalian cardiomyocyte (depending on species and health) and are regimentally arranged to supply 95% of cellular energy (for review see Ref. 20) via creatine kinase shuttle systems coupled to energy consumption sites (33,40,41). In hypertension-mediated hypertrophy and resulting heart failure, functional disruption occurs at all these levels (33), with changes in respiration (14,15,22,23,28,47), energy transfer (33, 53), and ATP consumption (55).In the context of heart failure (33), there has been a particular focus on mitochondria and energy transfer within the cardiomyocyte. This has driven many to study mitochondria in isolation and in vivo using NMR (4...

Differences in left ventricular cardiomyocyte loss induced by chronic intermittent hypoxia between spontaneously hypertensive and Wistar–Kyoto rats

“…According to a previous study, when cardiomyocytes had been subjected to hypoxia for 24-72 h, the proportion of cells capturing PI increased from 10% to 48% [5]. Since PI positivity indicates plasma membrane rupture, the abovementioned studies indicate that higher oxidative stress leads to a depletion of ATP [28], which results in greater cardiomyocyte necrosis [29,30] from cell membrane damage [5], ultimately resulting in greater cardiomyocyte loss. Therefore, our findings show that when SHR were exposed to CIH, the increase in PI-positive cells was greater than that in WKY, such that the cell membrane disruption was higher in SHR than in WKY.…”

“…Furthermore, an increase in oxidative stress reduces the amount of ATP available to the myocardium [28]. When cellular ATP is inadequate, the ratio of cells undergoing apoptosis to those undergoing necrosis decreases [29,30].…”

Ob/ob Mouse Livers Show Decreased Oxidative Phosphorylation Efficiencies and Anaerobic Capacities after Cold Ischemia

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“…Images were acquired at the following magnifications, ×5600, ×8800 and ×66000, using a Phillips CM-10 transmission electron microscope (Eindhoven, The Netherlands). Analysis of mitochondrial surface density (% cover) and cristae density (cristaeµm −1 ) was performed in ImageJ software (v. 1.45, National Institutes of Health, Bethesda, MD, USA) using protocols described by Hickey and colleagues (Hickey et al, 2009). …”