Re-examination of the carotid body ultrastructure with special attention to intercellular membrane appositions.

Ultrathin sections of the carotid body of adult rats, processed through freeze-substitution after aldehyde-prefixation, showed a substantial number of presumed gap junctions between two adjacent chief cells, between chief and sustentacular cells, and between chief cells and carotid nerve terminals. The junctions showed a very narrow intercellular space of 2 nm and ranged in length from 200 nm to 1 micron. They may form the morphological substrate for electrical coupling between cells, the occurrence of which has been demonstrated by electrophysiology. Further studies using freeze-fracture and immunocytochemistry for connexins are necessary to confirm this possibility. In addition, small tight junctions are present between chief and sustentacular cells, and between adjacent sustentacular cells.