Are myocardial eNOS and nNOS involved in the β-adrenergic and muscarinic regulation of inotropy? A systematic investigation

The role of constitutive nitric oxide (NO) production in the regulation of beta-adrenergic and muscarinic responses remains controversial. Conflicting data in left ventricular (LV) myocytes from eNOS knockout mice (eNOS-/-) have been ascribed to inconsistent experimental conditions (i.e., differences in the choice of controls, age of the mice, myocytes' stimulation frequency, and in the level of beta-adrenergic stimulation); however, the recent identification of a neuronal-like NO synthase (nNOS) in the LV myocardium has raised the possibility that this isoform may be involved in the modulation of beta-adrenergic and muscarinic responses.