Modulation of in vivo cardiac function by myocyte-specific nitric oxide synthase-3

Nitric oxide ( NO) functions principally as a diffusible paracrine effector. The exception is in cardiomyocytes where both NO synthases ( NOS) and target proteins coexist, allowing NO to work in an autocrine/ intracrine fashion. However, the most abundant myocyte isoform ( NOS3) is far more expressed in vascular endothelium; thus, the in vivo contribution of myocyte- NOS3 remains less clear. The present study tested this role by transfecting whole hearts of NOS3- null ( NOS3(-/-)) mice with adenovirus- expressing NOS3 coupled to alpha-MHC promoter ( AdV(NOS3)), comparing results to hearts transfected with marker-gene beta-galactosidase ( AdV beta(gal)). Total myocardial NOS3 protein and activity were restored to near wild- type ( WT) levels in NOS3(-/-) +AdV(NOS3) hearts, and NOS3 relocalized normally with caveolin- 3. Ejection function by pressure- volume analysis was enhanced in NOS3(-/-) +AdVbeta(gal) over WT or NOS3(-/-) +AdV(NOS3). More prominently, isoproterenol ( ISO)- stimulated systolic and diastolic function in WT was amplified in NOS3(-/-) +AdVbeta(gal), whereas NOS3(-/-) +AdV(NOS3) returned the response to control. ISO- activated systolic function was inhibited 85% by concomitant muscarinic stimulation ( carbachol) in NOS3(-/-) +AdV(NOS3) but not NOS3(-/-) +AdVbeta(gal) hearts. Lastly, NOS3(-/-) +AdVbeta(gal) mice displayed enhanced inotropy and lusitropy over WT at slower heart rates but a blunted rate augmentation versus controls. A more positive rate response was restored in NOS3(-/-) +AdV(NOS3) ( P < 0.001). Thus, myocyte autocrine/ intracrine NOS3 regulation in vivo can underlie key roles in beta- adrenergic, muscarinic, and frequency- dependent cardiac regulation.