Hoppel 2018 MiPschool Tromso D1

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Charles Hoppel
Two populations of muscle mitochondria: heart and skeletal muscle.

Link: MitoEAGLE

Hoppel CL (2018)

Event: MiPschool Tromso-Bergen 2018


Based on morphology of cardiac muscle cells, mitochondria are located under the sarcolemma, between the myofibrils, and in the central perinuclear region. Using concepts of cellular enzymology, protein yields, transmission electron microscopy (TEM) by Drs. Bernard Tandler and Hisashi Fujioka, high-resolution scanning electron microscopy (HRSEM) with Dr. Alessandro Riva, and functional studies with Dr. June Palmer, methods were devised to remove the sarcolemma from heart tissue producing a skinned myofibril releasing of a specific population of mitochondria, dubbed subsarcolemmal mitochondria (SSmt). The resultant myofibril pellet was then subjected to protease treatment to disrupt the fibrils, leading to liberation of mitochondria from the interfibrillar space (IFmt). The overall recovery of mitochondria was 70 -80% with only 5% released into the supernatants and the remaining ~20% entrapped in the tissue debris consisting largely of digested myofibrils. The content of mitochondrial enzymes and activity of oxidative phosphorylation is @150% in IFmt compared to the SSmt. Of the multiple examples of pathophysiological changes found only in one population, we will focus on the cardiomyopathy in the Syrian Hamster (only IFmt affected), diabetes mellitus in the rat (only SSmt affected), and aging in the rat heart (only the IFmt involved). Because of the location of the IFmt and t-tubule system in proximity of the intercalated discs, the involvement and interaction of these with Ca2+ signaling in cardiac excitation-contraction coupling (E-C) has been explored.

In skeletal muscle there is controversy as to whether the mitochondria exist as a reticulum or as distinct entities. There are more studies published using the two populations of skeletal muscle mitochondria than from heart. We were unable to prepare purified SSmt from skeletal muscle as judged by transmission electron microscopy, because of the presence of vesicles of undetermined origin. Attempts to remove these contaminants were unsuccessful (unpublished with Dr. Linda Brady). When we switched from using the Polytron homogenizer to disrupt the sarcolemma in muscle tissue to using proteolytic enzymes (collagenase for heart and dispase for skeletal muscle) to expose the sarcolemma so that a gentle physical force could be applied (Potter-Elvehjem homogenizer) to disrupt that plasma membrane, we observed a remarkable diminution in the presence of vesicles in the SSmt. Nicola Lai modified the skeletal muscle procedure to maximize SSmt and IFmt recovery (overall ~80%) while preserving mitochondrial integrity, function, and structure. We will discuss the skeletal muscle mitochondrial observations in a model of pacing-induced heart failure in a dog model. The decrease in respiratory rates of skeletal muscle SSmt are neither relieved upon collapsing the mitochondrial potential with an uncoupler nor increased in the presence of maximal ADP concentrations, showing a defect in the ETC. In contrast, respiratory rates of skeletal muscle IFmt from HF were relieved with the uncoupler and partially improved in the presence of maximal ADP concentrations. These IFmt alterations in the phosphorylation apparatus were detected with a decreased amount of ANT isoform 2 and increased amount of isoform 1. The IFmt dysfunction may be explained by this shift in ANT isoforms.

In conclusion, the study of the two populations of muscle mitochondria is necessary to truly understand the presence and type of dysfunction.

Bioblast editor: Beno M, Plangger M O2k-Network Lab: US OH Cleveland Hoppel CL


Dept Pharmacology Medicine, Case Western Reserve Univ School Medicine, Cleveland, OH, USA

MitoEAGLE recommendations: harmonization of nomenclature

  • Gnaiger 2019 MitoFit Preprint Arch: The general abbreviation for 'mitochondria' or 'mitochondrial' (compare mtDNA) is 'mt'
  • IFM was converted to IFmt
  • SSM was converted to SSmt

Labels: MiParea: Respiration, Comparative MiP;environmental MiP  Pathology: Aging;senescence, Diabetes, Myopathy 

Organism: Rat, Dog, Other mammals  Tissue;cell: Heart, Skeletal muscle  Preparation: Isolated mitochondria 

Coupling state: OXPHOS 

HRR: Oxygraph-2k  Event: D1, Oral