Nitric oxide is not involved in the endotoxemia-induced alterations in Ca2+ and ryanodine responses in mouse diaphragms.
Lipopolysaccharide (LPS, endotoxin)-induced diaphragmatic contractile dysfunction and sarcolemmal injury in animals has been identified. However, the precise nature of sepsis-related alterations in diaphragm myofiber function and the activity of Ca(2+) release from sarcoplasmic reticulum of skeletal muscle remain unclear. The present study investigated the in vivo effects of LPS on the Ca(2+)-dependent mechanical activity and ryanodine response in mouse diaphragm and Ca(2+) release from isolated sarcoplasmic reticulum membrane vesicles, and aimed to examine the role of nitric oxide (NO) in these responses. When diaphragms were bathed in a solution that was Cl(-)-free, Na(+)-free, but contained high K(+), a Ca(2+)-induced contracture was elicited. Increases in external Ca(2+) concentration produced increases in peak tension of Ca(2+)-induced contracture in control diaphragm, while a decrease was seen in endotoxemic diaphragm. Ryanodine induced a marked contracture in control diaphragms, which was diminished after endotoxemia. This finding is correlated with the decrease of ryanodine-induced Ca(2+) release and the suppression of [(3)H]ryanodine binding on the isolated SR of the skeletal muscle from LPS-treated rats. In mice treated with LPS significantly increased levels of plasma nitrite and serum TNF-alpha were observed, changes inhibited by aminoguanidine [an inhibitor of inducible NO synthase (iNOS)] and pentoxifylline (an inhibitor of tumor necrosis factor-alpha formation), respectively. Moreover, LPS treatment resulted in a significant expression of mRNA for iNOS in mouse diaphragms. The inhibitory effects on Ca(2+)- and ryanodine responses by LPS could be prevented by treatment with polymyxin B (LPS neutralizer) and pentoxifylline, but not by treatment with dexamethasone, N(G)-nitro- L-arginine or aminoguanidine (NOS inhibitors). These results imply that the NO-related pathway may not be involved in the dysfunction of the Ca(2+) release mechanism in the sarcoplasmic reticulum of mouse diaphragm during endotoxemia.
Liu
Shing-Hwa
SH
Institute of Toxicology, College of Medicine, National Taiwan University, No. 1, Jen-Ai Road, Section 1, Taipei 10043, Taiwan. shliu@ha.mc.ntu.edu.tw
Lai
Jiun-Li
JL
Yang
Rong-Sen
RS
Lin-Shiau
Shoei-Yn
SY
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D003964:Diaphragm / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D019446:Endotoxemia / Q000139:chemically induced / Q000201:enzymology / Q000378:metabolism*; D008070:Lipopolysaccharides / Q000633:toxicity; D008297:Male; D051379:Mice; D008813:Mice, Inbred ICR; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology; D009569:Nitric Oxide / Q000037:antagonists & inhibitors / Q000378:metabolism*; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D012433:Ryanodine / Q000494:pharmacology*
D008070:Lipopolysaccharides; D012433:Ryanodine; D009569:Nitric Oxide; D019001:Nitric Oxide Synthase; D002118:Calcium