Evidence For The Existence Of A Constitutive Nitric Oxide Synthase In Vascular Smooth Muscle

SUMMARY1. We have identified a neuronal nitric oxide synthase (NOS)‐like constitutive form of NOS in vascular smooth muscle (VSM) using a functional contractility approach as well as immunohistochemical methods.2. NG‐Nitro‐L‐arginine methyl ester, NG‐monomethyl‐L‐ arginine and NG‐nitro‐L‐arginine (L‐NOARG), the competitive inhibitors of NOS, inhibited Mg2+‐induced relaxation of de‐endothelialized rat aorta precontracted with phenylephrine (PE). This Mg2+ relaxation of VSM was not affected by inhibitors of inducible NOS.3. Electrical field stimulation (EFS; 30–70 Hz) caused relaxation of rat aorta in the presence of tetrodotoxin (therefore not a neurogenic effect) and this EFS relaxation was effectively inhibited by L‐NOARG, oxyhemoglobin and methylene blue.4. Immunohistochemical studies of dog saphenous vein using antibodies raised against neuronal NOS indicated prominent staining along the plasmalemma in a punctate pattern similar to the distribution of antibodies against caveolin‐1, a major constituent of the plasmalemmal caveolae.5. We propose that a constitutive NOS of non‐endothelial, non‐neuronal origin is present in a special caveolae domain of VSM cell membranes and could be activated by an ionic mechanism yet to be characterized.

Evidence For The Existence Of A Constitutive Nitric Oxide Synthase In Vascular Smooth Muscle Journal Articles