2012 OSU Molecular Life Sciences
Interdisciplinary Graduate Programs Symposium

 

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Poster number 29 submitted by Lifei Tang

Neuronal nitric oxide synthase contributes to the positive inotropic effect of beta-adrenergic stimulation via Ca2+/calmodulin-dependent protein kinase II activation

Lifei Tang (Department of Physiology and Cell Biology), Steve R. Roof (Department of Physiology and Cell Biology), Jerry Curran (The Dorothy M. Davis Heart and Lung Research Institute), Peter J. Mohler (The Dorothy M. Davis Heart and Lung Research Institute), Thomas R. Shannon (Rush University)

Abstract:
RATIONALE: Stimulation of the beta-adrenergic (beta-AR) pathway leads to positive inotropy, and is the major regulator of heart function. Our previous work has shown that NOS1 can modulate the functional response to beta-AR stimulation. However, the molecular mechanisms of this modulation are unknown. OBJECTIVE: The purpose of this study is to determine how NOS1 signaling contributes to the positive inotropic effect of beta-AR stimulation. METHODS AND RESULTS: Akt (Inhibitor V) and CaMKII (KN93) inhibition decreased the contractile response (Ca2+ transients-Fluo-4, cell shortening-edge detection) to isoproterenol (ISO, non-specific beta-AR agonist) in wildtype (WT, C57Bl6)ventricular myocytes. Furthermore, in WT myocytes, beta-AR stimulation increased ryanodine receptor(RyR) activity (SR Ca2+ leak/load relationship) via CaMKII activation (autophosphorylation at Thr287). Interestingly, Akt and CaMKII inhibition had no effect on the already reduced contractile response to ISO in NOS1 knockout (NOS1-/-) myocytes. Moreover, in NOS1-/- myocytes, ISO did not increase RyR activity nor activate CaMKII. We also observed that nitric oxide is able to directly increase the activity of purified CaMKII (32P incorporation into the β2a-subunit of the L-type Ca channel). CONCLUSION: These data suggest that during beta-AR stimulation, NOS1 is activated by Akt, which then directly actuates CaMKII to increase RyR activity contributing to the positive inotropy. Further study of this pathway is warranted since CaMKII expression and activity are increased in cardiac hypertrophy and heart failure. A better understanding of the NOS1/CaMKII pathway during beta-AR stimulation has beneficial therapeutic potential for heart disease.

Keywords: NOS1, CaMKII, Akt