Aim: To study the cell-type specific subcellular distribution of the three isoforms of nitric oxide synthase (NOS) in the rat duodenum.
Methods: Postembedding immunoelectronmicroscopy was performed, in which primary antibodies for neuronal NOS (nNOS), endothelial NOS (eNOS), and inducible NOS (iNOS), were visualized with protein A-gold-conjugated secondary antibodies. Stained ultrathin sections were examined and photographed with a Philips CM10 electron microscope equipped with a MEGAVIEW II camera. The specificity of the immunoreaction in all cases was assessed by omitting the primary antibodies in the labeling protocol and incubating the sections only in the protein A-gold conjugated secondary antibodies.
Results: Postembedding immunoelectronmicroscopy revealed the presence of nNOS, eNOS, and iNOS immunoreactivity in the myenteric neurons, the enteric smooth muscle cells, and the endothelium of capillaries running in the vicinity of the myenteric plexus of the rat duodenum. The cell type-specific distributions of the immunogold particles labeling the three different NOS isozymes were revealed. In the control experiments, in which the primary antiserum was omitted, virtually no postembedding gold particles were observed.
Conclusion: This postembedding immunoelectronmicroscopic study provided the first evidence of cell-type-specific differences in the subcellular distributions of NOS isoforms.
Keywords: Endothelial nitric oxide synthase; Inducible nitric oxide synthase; Neuronal nitric oxide synthase; Postembedding immunoelectronmicroscopy; Subcellular distribution.