T-0156, a novel phosphodiesterase type 5 inhibitor, and sildenafil have different pharmacological effects on penile tumescence and electroretinogram in dogs

Stimulus-specific blockade of nitric oxide-mediated dilatation by asymmetric dimethylarginine (ADMA) and monomethylarginine (L-NMMA) in rat aorta and carotid artery

Previous work on female rat aorta has shown that although monomethylarginine (L-NMMA) and asymmetric dimethylarginine (ADMA) each enhance submaximal phenylephrine-induced tone, consistent with blockade of basal nitric oxide activity, neither agent has any major effect on acetylcholine-induced relaxation. The aim of this study was to adopt a variety of different experimental approaches to test the hypothesis that these methylarginines block basal but not agonist-stimulated activity of nitric oxide. Basal activity of nitric oxide was assessed by observing the rise in submaximal phenylephrine-induced tone produced by nitric oxide synthase (NOS) inhibitors in male and female aorta and female carotid artery, and by monitoring the vasodilator actions of superoxide dismutase (SOD) or the PDE 5 inhibitor, T-0156. Agonist-stimulated activity of nitric oxide was assessed by observing the relaxant actions of acetylcholine or calcium ionophore A23187. L-NMMA, ADMA and L-NAME (100 μM) each enhanced submaximal phenylephrine-induced tone and inhibited SOD- or T-0156-induced relaxation, consistent with each NOS inhibitor blocking basal nitric oxide activity. In contrast, L-NMMA and ADMA had little effect on acetylcholine- or A23187-induced relaxation, while L-NAME produced powerful blockade. These observations provide support for the hypothesis that L-NMMA and ADMA selectively block basal over agonist-stimulated activity of nitric oxide in rat vessels.

Phosphodiesterase 5 restricts NOS3/Soluble guanylate cyclase signaling to L-type Ca2+ current in cardiac myocytes

Endothelial nitric oxide synthase (NOS3) regulates the functional response to beta-adrenergic (beta-AR) stimulation via modulation of the L-type Ca(2+) current (I(Ca)). However, the NOS3 signaling pathway modulating I(Ca) is unknown. This study investigated the contribution of soluble guanylate cyclase (sGC) and phosphodiesterase type 5 (PDE5), a cGMP-specific PDE, in the NOS3-mediated regulation of I(Ca). Myocytes were isolated from NOS3 knockout (NOS3(-/-)) and wildtype (WT) mice. We measured I(Ca) (whole-cell voltage-clamp), and simultaneously measured Ca(2+) transients (Fluo-4 AM) and cell shortening (edge detection). Zaprinast (selective inhibitor of PDE5), decreased beta-AR stimulated (isoproterenol, ISO)-I(Ca), and Ca(2+) transient and cell shortening amplitudes in WT myocytes. However, YC-1 (NO-independent activator of sGC) only reduced ISO-stimulated I(Ca), but not cardiac contraction. We further investigated the NOS3/sGC/PDE5 pathway in NOS3(-/-) myocytes. PDE5 is mislocalized in these myocytes and we observed dissimilar effects of PDE5 inhibition and sGC activation compared to WT. That is, zaprinast had no effect on ISO-stimulated I(Ca), or Ca(2+) transient and cell shortening amplitudes. Conversely, YC-1 significantly decreased both ISO-stimulated I(Ca), and cardiac contraction. Further confirming that PDE5 localizes NOS3/cGMP signaling to I(Ca); YC-1, in the presence of zaprinast, now significantly decreased ISO-stimulated Ca(2+) transient and cell shortening amplitudes in WT myocytes. The effects of YC-1 on I(Ca) and cardiac contraction were blocked by KT5823 (a selective inhibitor of the cGMP-dependent protein kinase, PKG). Our data suggests a novel physiological role for PDE5 in restricting the effects of NOS3/sGC/PKG signaling pathway to modulating beta-AR stimulated I(Ca), while limiting effects on cardiac contraction.