Abstract P3133: Role Of Myofilament-associatedNeuronal NOSFor Ca 2+ Desensitization Via Troponin I Phosphorylation In The Right Ventricular Cardiomyocytes Of Rats

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This study aimed to compare the role of neuronal nitric oxide synthase (nNOS, NOS1) in the excitation-contraction coupling and myofilament Ca 2+ -sensitivity between left ventricular cardiomyocytes (LVCMs) and right ventricular cardiomyocytes (RVCMs). Previous research had only investigated the effects of nNOS on LVCMs, but our study focused on RVCMs which have slightly larger diastolic sarcomere length (SL D ) and smaller sarcomere shortening (ΔSL) than LVCMs. Immunoblot study showed that the total expression and phosphorylated Ser 1417 ratio of nNOS were not different between RVCMs and LVCMs. However, treating RVCMs with the nNOS-specific inhibitor, S-methyl-L-thiocitrulline (SMTC), resulted in more prominent augmentation of ΔSL and shortened SL D in RVCMs, along with a paradoxical decrease of the amplitude of Ca 2+ transient (Δ[Ca 2+ ] i ) due to a more significant inhibition of L-type Ca 2+ current in RVCMs. The Ca 2+ -contraction loop showed a more leftward shift in the RVCMs by nNOS inhibition, indicating Ca 2+ desensitization of the myofilaments by the intrinsic nNOS. Previous studies offered troponin I (cTnI) phosphorylation as the regulatory target of myofilament Ca 2+ -sensitivity through the sGC-cGMP-PKG pathway downstream to NO. The SMTC treatment decreased cTnI phosphorylation in the RVCMs, while not in the LVCMs, suggesting that nNOS plays a more prominent role in myofilament Ca 2+ desensitization in RVCMs by targeting cTnI. Additionally, the higher phosphorylation of nNOSβ, the isoform of nNOS expressed in the myofilaments, was detected in the myofilament of RVCMs than LVCMs. This study is the first to demonstrate the more significant role of nNOS in RVCMs in regulating myofilament Ca 2+ desensitization through cTnI.