Electron-dense endoplasmic reticulum-like profiles closely associated with mitochondria in glomus cells of the carotid body after fixation with oxalate.

Fixation in the presence of oxalate was used to demonstrate the electron-dense Ca2+ precipitates in the endoplasmic reticulum in glomus cells of the carotid body. Glomus cells in intact carotid bodies or cells dissociated from the organ by treatment with collagenase were studied electron microscopically. In the intact organ as well as in dissociated glomus cells, electron-dense endoplasmic reticulum-like profiles were seen closely associated with mitochondria, while these lacked reaction product. The interspace between mitochondria was occupied by electron-dense, slightly distended ER, which appeared to contact the outer membrane of the mitochondria. Occasionally, a mitochondrion was in contact with several ER profiles or the ER formed an electron-dense 'cap' on the mitochondrion. The electron-dense precipitates could be removed from ultrathin sections with the calcium chelator ethyleneglycol-2(2-aminoethyl tetra-acetic acid) (EGTA). It is tentatively suggested that the endoplasmic reticulum could be involved in intracellular buffering of Ca2+ in the glomus cell, as has been previously suggested for neurons.