Structural differences in two biochemically defined populations of cardiac mitochondria

Abstract

To determine whether there are structural differences in two topologically separated, biochemically defined mitochondrial populations in rat heart myocytes, the interior of these organelles was examined by high-resolution scanning electron microscopy. On the basis of a count of 159 in situ subsarcolemmal mitochondria (SSM, i.e., those that directly abut the sarcolemma), these organelles possess mainly lamelliform cristae (77%), whereas the cristae in in situ interfibrillar mitochondria (IFM, i.e., those situated between the myofibrils, n = 300) are mainly tubular (55%) or a mixture of tubular and lamelliform (24%). Isolated SSM (n = 374), similar to their in situ counterparts, have predominantly lamelliform cristae (75%). The proportions of crista types in isolated IFM (n = 337) have been altered, with only 20% of these organelles retaining exclusively tubular cristae, whereas 58% are mixed; of the latter, lamelliform cristae predominate. This finding suggests that, in contrast to SSM, the cristae in IFM are structurally plastic, changing during isolation. These observations on >1,000 organelles provide the first quantitative morphological evidence for definitive differences between the two populations of cardiac mitochondria.

Structure of cristae in cardiac mitochondria of aged rat

“…It appears that aging-related biochemical defects do not affect the configuration of the mitochondrial cristae, even though this is where the electron transport chain complexes reside that are compromised with age. In the Sprague-Dawley rat strain, major differences between SSM and IFM were clearly evident by HRSEM (Riva et al, 2005).The profound biochemical changes that we have described in IFM are not paralleled by similar age-related alterations in crista morphology. It is obvious in the aged Fischer 344 rat that the biochemical performance of mitochondria is not in lock-step with morphology.…”

“…It appears that aging-related biochemical defects do not affect the configuration of the mitochondrial cristae, even though this is where the electron transport chain complexes reside that are compromised with age. In the Sprague-Dawley rat strain, major differences between SSM and IFM were clearly evident by HRSEM (Riva et al, 2005).…”

“…Specimens of both in situ tissues and mitochondrial pellets were prepared for HRSEM by our previously published protocol (Riva et al, 1999;Riva et al, 2005). Fixed solid tissues were sectioned at 150 μm with a Sorvall TC2 tissue sectioner at room temperature.…”

“…Our use of osmium extraction-HRSEM allowed us to establish the threedimensional structure of cristae in more than a thousand in situ and isolated cardiac mitochondria in or derived from young adult Sprague-Dawley rats (Riva et al, 2005). SSM contain largely lamelliform cristae; in contrast, cristae in IFM display mostly tubular morphology (Riva et al, 2005). This result provides a morphological underpinning for the Corresponding Author: Charles L. Hoppel, M.D., Case Western Reserve University School of Medicine, Department of Pharmacology, 10900 Euclid Avenue, Cleveland, Phone: (216) FAX: (216) 368-3395, E-mail: charles.hoppel@case.edu Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication.…”

“…With this technique, it is possible to examine the internal organization, i.e., crista configuration, of vast numbers of organelles with relative ease. As a baseline for the current study, we examined by HRSEM the cardiac mitochondria of adult Sprague-Dawley rats (Riva et al, 2005). In this rat strain, 77% of the in situ SSM had lamelliform cristae exclusively, whereas of the IFM 55% were tubular and 24% mixed.…”