The subcellular localization of neuronal nitric oxide synthase determines the downstream effects of NO on myocardial function

Methods and results Adenoviruses (AdV) encoding for a human nNOS. eGFP fusion protein or eGFP were injected into the left ventricle (LV) of nNOS(-/-) mice. nNOS. eGFP localized to the sarcolemmal and t-tubular membrane and immunoprecipitated with syntrophin and caveolin-3 but not with RyR2. Myocardial transduction of nNOS. eGFP resulted in a significantly increased NOS activity (10-fold, P < 0.01), a 20% increase in myocardial tetrahydrobiopterin (BH4) (P < 0.05), and a 30% reduction in superoxide production (P < 0.001). LV myocytes transduced with nNOS. eGFP showed a significantly lower basal and beta-adrenergic stimulated ICa, [Ca2+] i transient amplitude and cell shortening (vs. eGFP). All differences between groups were abolished after NOS inhibition. In contrast, nNOS. eGFP had no effect on RyR nitrosylation, PLB phosphorylation or the rate of myocardial relaxation and [Ca2+] i decay.

Aims In healthy hearts, the neuronal nitric oxide synthase (nNOS) is predominantly localized to the sarcoplasmic reticulum (SR), where it regulates the ryanodine receptor Ca2+ release channel (RyR2) and phospholamban (PLB) phosphorylation, and to a lesser extent to the sarcolemmal membrane where it inhibits the L-type Ca2+ current (I-Ca). However, in failing hearts, impaired relaxation and depressed inotropy are associated with a larger proportion of nNOS being localized to the sarcolemmal membrane. Whether there is a causal relationship between altered myocardial function and subcellular localization of nNOS remains to be assessed.