Diaphragm injury and myofibrillar structure induced by resistive loading

The purpose of this study was to determine whether ventilatory failure is associated with muscle fiber damage and myofibrillar protein alterations. Ventilatory failure was induced by tightening a polyvinyl band around the trachea of hamsters (TB; n = 14) for 6 days, which resulted in severe respiratory acidosis (PCO2: 97.9 +/- 29.6 vs. 51.6 +/- 19.6 Torr; pH: 7.16 vs. 7.35), hypoxemia (PO2: 42.8 +/- 16.8 vs. 65.9 +/- 25.8 Torr), and increased pulmonary resistance (1.89 +/- 1.61 vs. 0.29 +/- 0.27 cmH2O.ml-1 x min; P < 0.05). The point-counting technique of hematoxylin- and eosin-stained cross sections showed a higher area fraction of abnormal muscle and inflammatory cells in the costal [0.133 +/- (SE) 0.33 vs. 0.040 +/- 0.010] and crural regions (0.069 +/- 0.020 vs. 0.012 +/- 0.003) of the diaphragm in TB hamsters than in control hamsters. Electron micrographs revealed sarcomeric disruption and Z band streaming in the diaphragm of TB hamsters. Myofibrillar changes of the diaphragm associated with ventilatory failure were quantitative (i.e., a lower yield of purified myofibrils) but not qualitative (similar sodium dodecyl sulfate-polyacrylamide gel electrophoresis protein profiles); however, sulfhydryl group reactivities were reduced (P < 0.05). Proteolysis of purified myofibrils from the diaphragm digested with calpain showed faster degradation rates for tropomyosin and alpha-actinin but not for all proteins for the TB animals. Ventilatory failure induced by resistive loading was associated with diaphragm injury; some of this injury was linked to changes in myofibrillar complexes, specifically their susceptibility to calpain-mediated degradation.