Lipopolysaccharide-induced diaphragmatic contractile dysfunction and sarcolemmal injury in mice lacking the neuronal nitric oxide synthase

In this study we evaluated the role of the neuronal nitric oxide synthase ( nNOS) in lipopolysaccharide (LPS)-induced diaphragmatic contractile dysfunc tion and sarcolemmal injury. Wild-type (WT) mice or mice deficient in the n NOS gene (nNOS(-/-)) were injected with either saline (control) or Escheric hia coil LPS (LPS groups) and sacrificed 12 h later. The diaphragm was then examined for NOS expression, NOS activity, and in-vitro contractility. We also assessed sarcolemmal injury in isolated muscle strips under resting co ndition and after 3 min of artificial stimulations. In WT mice, LPS injecti on reduced maximum force to about 75% of that of control animals and raised total NOS activity significantly due to the induction of the iNOS isoform. Although muscle fiber injury was minimal under resting condition, the perc entage of injured fibers in control and LPS-injected mice approached 27% an d 40% of total fibers, respectively, in response to artificial stimulation. By comparison, LPS injection in nNOS-/- mice elicited a worsening of muscl e contractility (maximum force < 60% of control animals) but elicited degre es of sarcolemmal injury similar to those observed in the WT animals. In ad dition, muscle NOS activity and iNOS protein level in nNOS(-/-) mice inject ed with LPS reached about 10% and 60% of that of WT animals, respectively ( p < 0.05 compared with WT animals). Protein level of endothelial NOS isofor m in the diaphragm was not altered by LPS injection in either WT or nNOS(-/ -) animals. We conclude that nNOS plays a protective role in attenuating th e negative influence of sepsis on diaphragmatic contractility but is not in volved in the pathogenesis of sepsis-induced sarcolemmal injury.