Skeletal Muscle NADPH Oxidase Is Increased and Triggers Stretch-Induced Damage in the mdx Mouse

Recent studies have shown that oxidative stress contributes to the pathogenesis of muscle damage in dystrophic (mdx) mice. In this study we have investigated the role of NADPH oxidase as a source of the oxidative stress in these mice. The NADPH oxidase subunits gp91phox, p67phox and rac 1 were increased 2–3 fold in tibilais anterior muscles from mdx mice compared to wild type. Importantly, this increase occurred in 19 day old mice, before the onset of muscle necrosis and inflammation, suggesting that NADPH oxidase is an important source of oxidative stress in mdx muscle. In muscles from 9 week old mdx mice, gp91phox and p67phox were increased 3–4 fold and NADPH oxidase superoxide production was 2 times greater than wild type. In single fibers from mdx muscle NADPH oxidase subunits were all located on or near the sarcolemma, except for p67phox,which was expressed in the cytosol. Pharmacological inhibition of NADPH oxidase significantly reduced the intracellular Ca2+ rise following stretched contractions in mdx single fibers, and also attenuated the loss of muscle force. These results suggest that NADPH oxidase is a major source of reactive oxygen species in dystrophic muscle and its enhanced activity has a stimulatory effect on stretch-induced Ca2+ entry, a key mechanism for muscle damage and functional impairment

Reciprocal regulation of mammalian nitric oxide synthase and calcineurin by plant calmodulin isoforms

Calmodulin (CaM) is the primary mediator of Ca signal transduction processes in cells. Unlike animal cells, plant cells express multiple CaM isoforms. One cloned soybean CaM isoform (SCaM-4) half-maximally activated mammalian nitric oxide synthase (NOS) at 180 nM while another (SCaM-1) served as a competitive antagonist (K(i) ≃ 120 nM) of this activation. The reciprocal was true for the protein phosphatase calcineurin (CAN); SCaM-1 half-maximally activated mammalian CaN at ~12 nM, and SCaM-4 competitively antagonized (K(i) ≃ 70 nM) its activation. The reciprocal enzyme activation and competitive inhibition exhibited by these plant CaM isoforms suggest that their differential expression in cells could allow selective activation of some target enzymes and the selective inhibition of others. This may allow for a branching or bifurcation in the Ca2+-CaM signal transduction pathway and to alterations in cell function.close394