Nitric oxide modifies the sarcoplasmic reticular calcium release channel in endotoxemia by both guanosine-3',5' (cyclic) phosphate-dependent and independent pathways.
OBJECTIVE
a) To determine whether decreased sarcoplasmic calcium release channel (CRC) activity is a mechanism by which myocardial contractility is reduced in endotoxemia; b) to determine whether nitric oxide modulates CRC activity in endotoxemia; and c) to examine two nitric oxide signaling pathways in relation to CRC function in endotoxemia.


METHODS
Randomized, prospective using a rat model of endotoxemia.


METHODS
: Research laboratory.


METHODS
Sprague-Dawley rats.


METHODS
Endotoxemia was induced by lipopolysaccharide administration. The effects of nitric oxide were studied using the highly selective inducible nitric oxide synthase inhibitor N-(3-(aminomethyl)benzyl)acetamidine dihydrochloride (1400W) and the specific guanylyl cyclase inhibitor 1-H (1, 2, 4)oxadiazolo[4,3-a]quinoxalin-1-one (ODQ).


RESULTS
We assessed myocardial contractility, myocardial nitric oxide content, and guanosine-3',5' (cyclic) phosphate (cGMP) content. We determined CRC activity by calcium release and ryanodine binding assays. We followed these variables at four time points through the course of endotoxemia. We found that myocardial contractility and CRC activity were decreased in late but not in early endotoxemia. Furthermore, inducible nitric oxide synthase inhibition with 1400W restored contractility and CRC activity in late endotoxemia but paradoxically worsened these variables in early endotoxemia. Through the use of the guanylyl cyclase inhibitor ODQ, we demonstrate that nitric oxide acts through cGMP-mediated mechanisms in early and late endotoxemia. We investigated cGMP-independent pathways by assessing the oxidative status of the CRC. We found that in late endotoxemia, nitric oxide decreased the number of free thiols, demonstrating that nitric oxide also acts through cGMP-independent pathways.


CONCLUSIONS
Nitric oxide has a dual effect on the CRC in endotoxemia. At low concentrations, as measured in early endotoxemia, nitric oxide stabilizes the CRC through cGMP-mediated mechanisms. In late endotoxemia, high nitric oxide concentrations decrease channel activity through both cGMP-dependent and cGMP-independent mechanisms.
Cohen
Rubin I
RI
North Shore-Long Island Jewish Institute for Medical Research, The Albert Einstein College of Medicine, New Hyde Park, NY, USA.
Wilson
David
D
Liu
Shu Fang
SF
D000818:Animals; D006152:Cyclic GMP / Q000378:metabolism*; D004195:Disease Models, Animal; D019446:Endotoxemia / Q000503:physiopathology* / Q000517:prevention & control; D008070:Lipopolysaccharides; D008297:Male; D009200:Myocardial Contraction / Q000502:physiology*; D009569:Nitric Oxide / Q000032:analysis / Q000378:metabolism; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors* / Q000378:metabolism; D018384:Oxidative Stress; D011897:Random Allocation; D051381:Rats; D017207:Rats, Sprague-Dawley; D012016:Reference Values; D019837:Ryanodine Receptor Calcium Release Channel / Q000187:drug effects / Q000378:metabolism*; D012680:Sensitivity and Specificity
D008070:Lipopolysaccharides; D019837:Ryanodine Receptor Calcium Release Channel; D009569:Nitric Oxide; D019001:Nitric Oxide Synthase; D006152:Cyclic GMP