Single-Cell Biophysics: Measurement, Modulation, and Modeling

Single-Cell Biophysics: Measurement, Modulation, and Modeling

Poster Abstracts

25-POS

Board 13

Sarcolemmal Biomechanics and Excitability in Cultured and Isolated Mechanically Muscle Fibers of Dystrophic Mice Karla P. Garcia-Pelagio 1,2 , Erick Hernandez-Ochoa 3 , Stephen J. Pratt 4 , Richard M. Lovering 4 . 1 Universidad Nacional Autonoma De Mexico, School Of Science, Physics Dept, Mexico City, Mexico, 2 University Of Maryland, School Of Medicine, Physiol Dept, Baltimore, MD, USA, 3 University Of Maryland, School Of Medicine, Biochem And Mol Biol Dept, Baltimore, MD, USA, 4 University Of Maryland, School Of Medicine, Orthopaedics Dept, Baltimore, MD, USA. Duchenne muscular dystrophy (DMD), the most common and severe dystrophy, is caused by the absence of dystrophin. Muscle weakness and fragility (i.e. increased susceptibility to damage) are presumably due to structural weakness of the myofiber cytoskeleton, but recent studies suggest that malformed/split myofibers in dystrophic muscle may also play a role. We have studied the biomechanical properties of the sarcolemma in: 1) Single myofibers isolated mechanically from extensor digitorum longus (EDL) muscles, and 2) Enzymatically-dissociated myofibers (both normal and malformed) from the flexor digitorum brevis muscle (FDB) in wild- type (WT) and dystrophic (mdx, mouse model for DMD) mice. Suction pressures (P) applied through a pipette to the membrane generated a bleb, which increased in height with increasing P. Larger increases in P ruptured the costameres, the connections between the sarcolemma and myofibrils, and eventually caused the sarcolemma to burst. The results from dissociated FDB and dissected EDL myofibers was higher in separation P up to 14-fold higher in the FDB than EDL. P at which the sarcolemma separated from the underlying myofibrils was 27% lower in mdx myofibers and 50% less in branches of split fibers compared to the trunk. We also asked whether the abnormal biomechanical phenotype of the MDX myofibers is associated with further deficits on excitable properties. To this end we use high-speed confocal microscopy and the voltage-sensitive indicator di-8-butyl-amino-naphthyl-ethylene-pyridinium-propyl-sulfonate. We found that the AP amplitude is not altered in MDX ‘normal’ or MDX ‘split’ FDB muscle fibers when compared to WT. Data indicate a reduction in muscle stiffness, increased sarcolemmal deformability and instability in mdx muscle. Findings also suggest mechanical differences due to altered morphology and technique of getting the fibers. Supported partially by PAPIIT-UNAM (IA210016) to KPGP and NIH to RML (R01AR059179).

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