Duchenne Muscular Dystrophy (DMD) is a recessive
X-linked genetic disease, caused by mutations in the gene encoding
dystrophin. DMD is characterized in humans and in mdx mice by a severe and progressive destruction of muscle fibers,
inflammation, oxidative/nitrosative stress, and cell death. In mdx muscle fibers, we have shown that basal
ATP release is increased and that extracellular
ATP stimulation is pro-apoptotic. In normal fibers, depolarization-induced
ATP release is blocked by
nifedipine, leading us to study the potential
therapeutic effect of
nifedipine in mdx muscles and its relation with extracellular
ATP signaling. Acute exposure to
nifedipine (10 µM) decreased [Ca(2+)]r, NF-κB activity and iNOS expression in mdx myotubes. In addition, 6-week-old mdx mice were treated with daily
intraperitoneal injections of
nifedipine, 1 mg/Kg for 1 week. This treatment lowered the [Ca(2+)]r measured in vivo in the mdx vastus lateralis. We demonstrated that extracellular
ATP levels were higher in adult mdx flexor digitorum brevis (FDB) fibers and can be significantly reduced after 1 week of treatment with
nifedipine. Interestingly, acute treatment of mdx FDB fibers with
apyrase, an
enzyme that completely degrades extracellular
ATP to
AMP, reduced [Ca(2+)]r to a similar extent as was seen in FDB fibers after 1-week of
nifedipine treatment. Moreover, we demonstrated that
nifedipine treatment reduced
mRNA levels of pro-oxidative/nitrosative (iNOS and gp91(
phox)/p47(
phox) NOX2 subunits) and pro-apoptotic (Bax) genes in mdx diaphragm muscles and lowered serum
creatine kinase (CK) levels. In addition,
nifedipine treatment increased muscle strength assessed by the inverted grip-hanging test and exercise tolerance measured with forced swimming test in mdx mice. We hypothesize that
nifedipine reduces basal
ATP release, thereby decreasing
purinergic receptor activation, which in turn reduces [Ca(2+)]r in mdx skeletal muscle cells. The results in this work open new perspectives towards possible targets for pharmacological approaches to treat DMD.