Ultrastructure of the glomus cells in the carotid body of chronically hypoxic rats: with special reference to the similarity of amphibian glomus cells.

The ultrastructural characteristics of the glomus cells in the rat carotid body exposed to extremely long-term hypoxia (10-12 weeks) were investigated. The glomus cells could be classified into four distinct types according to the shape of dense-cored vesicles in the glomus cell cytoplasm: 1) small vesicle cells (SVCs, 50 nm in mean diameter), 2) large vesicle cells (LVCs, 80 nm in mean diameter), 3) dilated eccentric vesicle cells (EVCs, 400-800 nm in diameter), and 4) mixed vesicle cells (MVCs, large and eccentric vesicles). Many clusters of glomus cells were found to contain all four categories of cell types. The appearance of EVCs was a unique and common characteristic of glomus cells in this long-term hypoxia model. We also noted other ultrastructural features with chronic hypoxia which are characteristic of the amphibian carotid labyrinth glomus cells: 1) incomplete covering of glomus cells with the supporting cell missing over a wide area, 2) long thin cytoplasmic projections in the intervascular stroma, and 3) intimate apposition of the glomus cells and pericytes (g-p connection), endothelial cells (g-e connection), plasma cells, and fibrocytes. Because arterial PO2 is generally low in amphibia, these may be general features of hypoxic adaptation and facilitate both uptake of oxygen from blood and release of catecholamine into the blood. The g-p and g-e connections may take part in the regulation of the microcirculation in the enlarged carotid body.