Abstract
Altered Ca
2+
homeostasis is a salient feature of heart disease, where the calcium release channel ryanodine receptor (RyR) plays a major role. Accumulating data support the notion that neuronal nitric oxide synthase (NOS1) regulates the cardiac RyR via
S
-nitrosylation. We tested the hypothesis that NOS1 deficiency impairs RyR
S
-nitrosylation, leading to altered Ca
2+
homeostasis. Diastolic Ca
2+
levels are elevated in NOS1
−/−
and NOS1/NOS3
−/−
but not NOS3
−/−
myocytes compared with wild-type (WT), suggesting diastolic Ca
2+
leakage. Measured leak was increased in NOS1
−/−
and NOS1/NOS3
−/−
but not in NOS3
−/−
myocytes compared with WT. Importantly, NOS1
−/−
and NOS1/NOS3
−/−
myocytes also exhibited spontaneous calcium waves. Whereas the stoichiometry and binding of FK-binding protein 12.6 to RyR and the degree of RyR phosphorylation were not altered in NOS1
−/−
hearts, RyR2
S
-nitrosylation was substantially decreased, and the level of thiol oxidation increased. Together, these findings demonstrate that NOS1 deficiency causes RyR2 hyponitrosylation, leading to diastolic Ca
2+
leak and a proarrhythmic phenotype. NOS1 dysregulation may be a proximate cause of key phenotypes associated with heart disease.
