Mechanical ventilation (MV) is a life-saving intervention for patients in
respiratory failure. However, prolonged MV causes the rapid development of diaphragm
muscle atrophy, and diaphragmatic weakness may contribute to difficult weaning from MV. Therefore, developing a therapeutic countermeasure to protect against MV-induced diaphragmatic
atrophy is important. MV-induced diaphragm
atrophy is due, at least in part, to increased production of
reactive oxygen species (ROS) from diaphragm mitochondria and the activation of key muscle
proteases (i.e.,
calpain and
caspase-3). In this regard, leakage of
calcium through the
ryanodine receptor (
RyR1) in diaphragm muscle fibers during MV could result in increased mitochondrial ROS emission,
protease activation, and diaphragm
atrophy. Therefore, these experiments tested the hypothesis that a pharmacological blockade of the
RyR1 in diaphragm fibers with
azumolene (AZ) would prevent MV-induced increases in mitochondrial ROS production,
protease activation, and diaphragmatic
atrophy. Adult female Sprague-Dawley rats underwent 12 hours of full-support MV while receiving either AZ or vehicle. At the end of the experiment, mitochondrial ROS emission,
protease activation, and fiber cross-sectional area were determined in diaphragm muscle fibers. Decreases in muscle force production following MV indicate that the diaphragm took up a sufficient quantity of AZ to block
calcium release through the
RyR1. However, our findings reveal that AZ treatment did not prevent the MV-induced increase in mitochondrial ROS emission or
protease activation in the diaphragm. Importantly, AZ treatment did not prevent MV-induced diaphragm fiber
atrophy. Thus, pharmacological inhibition of the
RyR1 in diaphragm muscle fibers is not sufficient to prevent MV-induced diaphragm
atrophy.