Concerted regulation of skeletal muscle contractility by oxygen tension and endogenous nitric oxide

Abstract

It is generally accepted that inhibition of nitric oxide synthase (NOS) facilitates, and thus nitric oxide (NO) inhibits, contractility of skeletal muscle. However, standard assessments of contractility are carried out at a nonphysiological oxygen tension [partial pressure of oxygen (pO2)] that can interfere with NO signaling (95% O2). We therefore examined, in normal and neuronal NOS (nNOS)-deficient mice, the influence of pO2 on whole-muscle contractility and on myocyte calcium flux and sarcomere shortening. Here, we demonstrate a significant enhancement of these measures of muscle performance at low physiological pO2 and an inhibitory influence at higher physiological pO2, which depend on endogenous nNOS. At 95% O2 (which produces oxidative stress; muscle core pO2 Ϸ400 mmHg), force production is enhanced but control of contractility by NO͞nitrosylation is greatly attenuated. In addition, responsivity to pO2 is altered significantly in nNOS mutant muscle. These results reveal a fundamental role for the concerted action of NO and O2 in physiological regulation of skeletal muscle contractility, and suggest novel molecular aspects of myopathic disease. They suggest further that the role of NO in some cellular systems may require reexamination. It has recently been recognized that redox-based regulation of protein function serves not only to mediate compensatory responses to oxidative or nitrosative stress but also modulates transduction along basic signaling pathways in mammalian cells (1). Further, accumulating evidence indicates that nitric oxide (NO)-based protein modifications are critical effectors of redox regulation, which may be linked at the molecular level to partial pressure of oxygen (pO 2 ) (1). Accordingly, the functional contribution of redox mechanisms remains, for the most part, untested, and potentially masked in virtually all ex vivo studies, which have been carried out at supranormal oxygen tension (typically 21% O 2 for cells and 95% O 2 for tissue, whereas pO 2 in vivo is much lower).Mammalian skeletal muscle operates over a range of pO 2 , which is determined by local blood flow and muscle activity, and contains endogenous sources of NO. The -isoform of type I or neuronal NO synthase (nNOS) localizes to the plasma membrane (sarcolemma) of skeletal muscle fibers through interaction with the dystrophin complex (2-4). In many mammals, nNOS is either restricted to or particularly abundant in fast-twitch fibers, although, in humans, fast-and slow-twitch fibers are more evenly endowed (2, 5, 6). The loss of nNOS from sarcolemma of mdx mice (whose fast-twitch fibers are disproportionately impaired), and of patients with Duchenne or Becker muscular dystrophy, focused interest on the possibility that NO produced by muscle fibers may play a role in excitation-contraction (E-C) coupling and that NO deficiency may contribute to contractile impairment in muscle disease (2-6). However, although mice deficient in nNOS show subtle abnormalities in muscle blood flow (7), overt alterations in contractile fun...

nNOS regulation of skeletal muscle fatigue and exercise performance

“…Thus, nNOSμ appears to be necessary for sustaining muscle force output during and immediately after exercise. These findings are in agreement with Eu et al (2003) who concluded that nNOSμ promotes contractility under low O 2 concentrations characteristic of working muscle. These data suggest that the adaptive increases in nNOSμ expression in response to endurance exercise may enhance skeletal muscle fatigue resistance and thus promote exercise performance.…”

“…The nNOS regulation of fatigue has been studied using a minimally invasive in situ approach that preserves muscle innervation, vascularization, temperature, and tissue O 2 concentrations (Percival et al , 2010. This approach is widely considered to be the most physiologically relevant method for measuring skeletal muscle fatigue and is especially useful given the known vasomodulatory function and exquisite oxygen sensitivity of nNOS enzymatic activity (Thomas et al 1998;Eu et al 2003;Stuehr et al 2004;Allen et al 2008).…”

Ryanodine Receptors: Structure, Expression, Molecular Details, and Function in Calcium Release

“…S-nitrosylation of Cys3635 has been shown to reverse the CaM inhibition on RyR1 and to activate the channel (Moore et al 1999b). The S-nitrosylation of Cys3635 appears to occur only at physiological tissue O 2 tension ( pO 2 ; 10 mm Hg) and facilitates muscle contraction (Eu et al 2003). Moreover, increased S-nitrosylationinduced RyR1 activity is suggested to sensitize RyR1 to environmental heat stress and MH crises (Durham et al 2008).…”

Regulation of the apoptosis–necrosis switch

“…It affects the cellular gene transcription machinery by inhibiting the DNA-binding activity of nuclear factor kB (NF-kB) (Matthews et al, 1996;Marshall and Stamler, 2001) and activator protein-1 (AP-1) (Tabuchi et al, 1994) or by activation of OxyR (Hausladen et al, 1996). NO nitrosylates thiol groups of cytosolic enzymes such as transglutaminase (Melino et al, 1997;Bernassola et al, 1999;Rossi et al, 2000), AP-1 Melino et al, 2000a), caspases (Dimmeler et al, 1997;Melino et al, 1997), glyceraldehyde-3-phosphate dehydrogenase (Mohr et al, 1996) hemoglobin (Jia et al, 1996;Gow and Stamler, 1998) and skeletal muscle (Stamler and Meissner, 2001;Eu et al, 2003), and it can modulate the biological activity of extracellular molecules such as coagulation factor XIII (Catani et al, 1998).…”