Functional expression of NOS 1 in vascular smooth muscle

Area of Science:

• Vascular biology
• Smooth muscle physiology
• Biochemistry

Background:

• Serotonin induces vascular smooth muscle (VSM) contraction by increasing intracellular calcium.
• Increased intracellular calcium activates Ca(2+)/calmodulin-dependent nitric oxide synthases (NOS), leading to cGMP production and protein kinase G (PKG) activation.
• PKG phosphorylates small heat shock protein 20 (HSP20).

Purpose of the Study:

• To investigate if serotonin activates a Ca(2+)-dependent NOS in VSM.
• To determine the role of NOS in serotonin-induced VSM responses.

Main Methods:

• Bovine carotid arterial smooth muscle strips were stimulated with serotonin.
• Nonspecific NOS inhibitor N-monomethyl-L-arginine (L-NMMA) and NOS 1-specific inhibitor 7-nitroindazole were used.
• cGMP levels and HSP20 phosphorylation were measured.
• Immunohistochemistry and Western blotting identified NOS isoforms.
• NOS activity was assessed by L-citrulline formation.
• High extracellular KCl-induced contractions were measured.

Main Results:

• Serotonin significantly increased cGMP and HSP20 phosphorylation in VSM.
• These increases were inhibited by L-NMMA.
• NOS 1 was identified in the VSM media, while NOS 3 was found only in the endothelium.
• NOS activity in smooth muscle was primarily NOS 1-dependent.
• NOS 1 inhibition augmented high KCl-induced contractions.

Conclusions:

• VSM contains functional NOS 1 that is activated by serotonin.
• NOS 1 activation influences VSM contractile responses.
• NOS 1 plays a role in regulating vascular smooth muscle tone.