An X chromosome-linked mouse mutant (mdx) has been investigated as an animal model of Duchenne's
muscular dystrophy, and has been found to have the same defect of
dystrophin in the muscle surface membrane. Intracellular recordings from the mdx mouse hemidiaphragm preparations revealed low resting membrane potentials and electrical
myotonia which occurred at the time of
microelectrode insertion and withdrawal. Electrical
myotonia of the mdx mouse was observed in 30-50% of the impaled muscle fibers at low temperature, which decreased to only 7.8% at 37 degrees C. Electrical
myotonia of mdx mice was not abolished by (+)-
tubocurarine. Though there was no behavioral
myotonia in mdx mice, repetitive bursts of action potentials in mdx mice were based on the abnormalities of the muscle membrane since neuromuscular blockade did not abolish the repetitive bursts. Also close observation of the
lenses of mdx mice revealed
cataracts from the newborn stage to the adult age.
Slit lamp examination of the
lenses of the mdx mice revealed nuclear
cataracts followed by anterior subcapsular
cataract as they grew. The
cataract of mdx mice is different from that of
myotonic dystrophy which is usually posterior subcapsular.