4 Characterisation of Mitochondrial Morphology in the Adult Rodent Heart. (19th January 2014) - Beikoghli Kalkhoran, S
Abstract : Rationale: In adult cardiomyocytes there are known to be 3 different sub-populations of mitochondria: Subsarcolemmal (SS), Interfibrillar (IF), and Perinuclear (PN), which appear to have distinctive properties and shapes. Here, we investigate the mitochondrial morphology of these 3 different mitochondrial subgroups and examine the effect of ischaemia on these parameters. Methodology: We investigated mitochondrial morphology in adult rodent hearts at baseline and in response to ischemia using electron microscopy (x3000 magnification). In six randomly selected electron micrographs of longitudinally-arranged cardiomyocytes, the following characteristics were determined (approx. 500 mitochondria in total): (1) Surface area (SA); (2) Fret's diameter (the longest distance between any points in a given mitochondrion); (3) Perimeter; (4) Aspect ratio: the length-to-width ratio; (5) Roundness: 4. SA/π.major axis2; (6) Circularity: 4π. SA/perimeter2 (1.0 indicates a perfect circle and as the value approaches zero it indicates an elongated shape). Results: In adult rat cardiomyocytes (n = 3 animals), IF mitochondria have a significantly greater SA [μm 2 ] (IF 0.37 ± 1.08 vs. SS 0.30 ± 1.07, PN 0.27 ± 1.03; P < 0.0001), Fret's diameter (IF 0.93 ± 0.02 vs. SS 0.83 ± 0.02, PN 0.79 ± 0.18, P < 0.0001), and Perimeter (IF 2.48 ± 1.08 vs. SS 2.21 ± 1.07 PN 2.11 ± 1.03, P < 0.0001), when compared to SSM and PN mitochondria. However, there were no major differences in Aspect ratio, Roundness or Circularity. IF mitochondria in the ischaemic adult murine heart had a smaller Area, Perimeter, Fret's diameter, Aspect ratio, and a greater degree of Roundness and Circularity. Conclusions: Interfibrillar mitochondria are generally larger and longer than SSM and PN mitochondria. In response to ischaemia, the IF mitochondria undergo fragmentation, generating smaller more rounded mitochondria.