Inotropic response to beta-adrenergic receptor stimulation and anti-adrenergic effect of ACh in endothelial NO synthase-deficient mouse hearts

1. The functional consequences of a lack of endothelial nitric oxide syntha se (eNOS) on left ventricular Force development and the anti-adrenergic gic effect of acetylcholine (ACh) M ere investigated in isolated hearts and ca rdiomyocytes from wild type (WT) and eNOS knockout (eNOS-/-) mice. 2. eNOS expression in cardiac myocytes accounted for 20% of total cardiac e NOS (Western blot analysis). These results were confirmed hv RT-PCR analysi s. 3. In the unstimulated perfused heart, the left ventricular pressure (LVP) and maximal rate of left ventricular force development (dP/dt(max)) of eNOS -/- hearts were not significantly different from those of WT hearts (LVP: 9 7 +/- 11 mmHg WT vs. 111 +/- 11 mmHg eNOS-/-; dP/dt(max): 3700 +/- 712 mmHg s(-1) WT vs. 4493 +/- 320 mmHg s(-1) eNOS-/-). 4. The dobutamine (10-300 nM)-induced increase in LVP was enhanced in eNOS- /- hearts. In contrast, L-tvpe Ca2+ currents (I-Ca,I-L) in isolated cardiom yocytes of WT and eNOS-/- heal ts showed no differences after beta -adrener gic stimulation. Dibutyryl-cGMP (50 muM) reduced basal I-Ca,I-L in WT cells to 72 +/- 12% while eNOS-/- I-Ca,I-L was insensitive to the drug. The pre stimulated I-Ca,I-L (30 nM isoproterenol) was attenuated by dibutyryl-cGMP in WT and eNOS-/- cells to the same extent. 5. The Ca2+ (1.5-4.5 mM)-induced increase in inotropy was not different bet ween the two experimental groups and P-adrenergic receptor density was incr eased by 50% in eNOS-/- hearts. 6. The contractile effects of dobutamine could be inhibited almost complete ly by ACh ol adenosine. The extent of the anti-adrenergic effect of both co mpounds was identical in WT and eNOS-/- hearts. Measurement of I-Ca,I-L in isolated cardiac myocytes yielded similar results. 7. These data demonstrate that in the Adult mouse (1) lack of eNOS is assoc iated with increased cardiac contractile force in response to beta -adrener gic stimulation and with elevated beta -adrenergic receptor density, (2) th e unaltered response of I-Ca,I-L in eNOS-/- cardiac myocytes to beta -adren ergic stimulation suggests that endothelium-derived NO is important in medi ating the whole-organ effects and (3) eNOS is unimportant fur the anti-adre nergic effect of ACh and adenosine.