Modulation of In Vivo Cardiac Function by Myocyte-Specific Nitric Oxide Synthase-3

Abstract—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 a -MHC promoter (AdVNOS3), comparing results to hearts transfected with marker-gene -galactosidase (AdVgal). Total myocardial NOS3 protein and activity were restored to near wild-type (WT) levels in NOS3/AdVNOS3 hearts, and NOS3 relocalized normally with caveolin-3. Ejection function by pressure-volume analysis was enhanced in NOS3/AdVgal over WT or NOS3/AdVNOS3. More prominently, isoproterenol (ISO)-stimulated systolic and diastolic function in WT was amplified in NOS3/AdVgal, whereas NOS3/AdVNOS3 returned the response to control. ISO-activated systolic function was inhibited 85 % by concomitant muscarinic stimulation (carbachol) in NOS3/AdVNOS3 but not NOS3/AdVgal hearts. Lastly, NOS3/AdVgal 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/AdVNOS3 (P0.001). Thus, myocyte autocrine/intracrine NOS3 regulation in vivo can underlie key roles in -adrenergic, muscarinic, and frequency-dependent cardiac regulation. (Circ Res. 2004;94:657-663.