Endothelial nitric oxide synthase and caveolin‐1 are co‐localized in sinusoidal endothelial fenestrae

Abstract: Background/Aims: Nitric oxide is synthesized in diverse mammalian tissues by a family of calmodulin‐dependent nitric oxide synthases (NOS). Caveolin, the principal structural protein in caveolae, interacts with endothelial NOS leading to enzyme inhibition in a reversible process modulated by Ca++‐calmodulin. The aim of the present study was to clarify the ultrastructural localization of eNOS and caveolin‐1 in hepatic sinusoidal endothelium by an electron immunogold method. Methods: Male Wistar rats were used. Liver tissues and hepatic sinusoidal endothelial cells isolated from rat livers by collagenase infusion were studied. For immunohistochemistry, liver specimens were reacted with anti‐eNOS or anti‐caveolin‐1 antibody. The ultrastructural localization of eNOS or caveolin‐1 was identified by electron microscopy using an immunogold post‐embedding method. Results: Immunohistochemical studies using liver tissues localized endothelial NOS in hepatic sinusoidal lining cells, portal veins and hepatic arteries; and caveolin‐1 in sinusoidal lining cells, bile canaliculi, portal vein and hepatic arteries. Immunogold particles indicating the presence of eNOS and caveolin‐1 were demonstrated on the plasma membrane of sinusoidal endothelial fenestrae in liver tissue and also in isolated sinusoidal endothelial cells. Conclusion: Endothelial NOS and caveolin are co‐localized on sinusoidal endothelial fenestrae, suggesting that interaction of the two may modulate cellular regulation of NO synthesis.