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

, Stephen J. Pratt

, Richard M. Lovering

Universidad Nacional Autonoma De Mexico, School Of Science, Physics Dept, Mexico City,

Mexico,

University Of Maryland, School Of Medicine, Physiol Dept, Baltimore, MD, USA,

University

Of Maryland, School Of Medicine, Biochem And Mol Biol Dept, Baltimore, MD, USA,

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).