Functional heterogeneity of mitochondria after cardiac cold ischemia and reperfusion revealed by confocal imaging

Abstract

Background. Mitochondria play a critical role in ischemia-reperfusion injury of the heart. The purpose of the present study was to analyze the intracellular region-specific functional state of mitochondria after cold ischemia-reperfusion in a rat heart transplant model.Methods. Imaging of the mitochondrial functional state in situ in nonfixed myocardial fibers was performed by confocal microscopy of mitochondrial flavoprotein autofluorescence as redox state indicator; fluorescence of Rhod-2, a specific probe for mitochondrial calcium; and of tetramethylrhodamine ethyl ester fluorescence to monitor the mitochondrial membrane potential.Results. This imaging demonstrated that, in contrast to control fibers, 10-hr heart cold storage, heterotopic cardiac transplantation, and 24-hr reperfusion result in a highly heterogeneous mitochondrial functional state (mitochondrial calcium content, redox state, and inner membrane potential), thus suggesting local permeability transitions and heterogeneous mitochondrial damage.Conclusions. Imaging of in situ mitochondria allows topologic assessment of mitochondrial defects and heterogeneity, consequently providing new insights into the mechanisms of cardiac ischemia-reperfusion injury.

β-Cell Mitochondria Exhibit Membrane Potential Heterogeneity That Can Be Altered by Stimulatory or Toxic Fuel Levels

“…In theory, a heterogeneous population may represent the existence of subpopulations of mitochondria that have relatively reduced capacity to generate secretagogues and thus constitute a therapeutic target for increased insulin secretion. To date, the phenomenon of mitochondrial heterogeneity has been studied in several cell types (7)(8)(9)(10)(11)(12) but not in ␤-cells.…”

“…Importantly, TMRE equilibration is rapid due to high permeability across membranes and it does not inhibit mitochondrial respiration in low concentrations (29). The dye concentrations used are lower than those previously reported in intact cell studies (7,8,29,30,31). This enabled minimal levels of cytotoxicity and self-quenching of the dyes.…”

High Glucose Disrupts Mitochondrial Morphology in Retinal Endothelial Cells

“…For example, studies investigating the ischemia-reperfusion model has shown that rat cardiomyocytes exhibit higher levels of heterogeneity after reperfusion. 30,31 Moreover, increased nutrient levels have been shown to increase mitochondrial membrane potential heterogeneity in pancreatic ␤ cells. 13 We report that an increase in mitochondrial heterogeneity coincides with the progression of RRECs through apoptosis.…”

Mitochondria: A mirror into cellular dysfunction in heart disease

“…The heterogeneous distribution of mitochondria throughout the cardiomyocyte, gives rise to functionally diverse subpopulations that are also subjected to physical and therefore functional alteration by fusion and fission cycles during physiological conditions and with acute and chronic CV disease [213]. Able to regulate mitochondrial morphology, fusion and fission events affect not only the mitochondrial membranes, but also the mitochondrial matrix, with respective sharing and splitting of matrix compartments.…”

“…I/R injury has been shown to result in increased mitochondrial heterogeneity across numerous functional parameters, including Ca 21 content, redox status and membrane potential, as measured by fluorescent confocal microscopy [207,213]. The rate of OxPhos was shown to decrease only in subsarcolemmal mitochondria, following 45 minutes global ischemia [214], while the loss of Dc M with I/R was shown to propagate [215] longitudinally from point of initiation, with overall heterogeneity in the spatial distribution of mitochondria affected [206].…”