Morphometric studies of dense-cored vesicles in type I cells of rat carotid body

Two subclasses of Type I cells of rat carotid body were recognized by analyzing the diameters of dense-cored vesicles. One group of cells contained vesicles with a mean diameter of about 52 nm; in the other group of cells the vesicles measured about 71 nm. The mean volume of the small vesicle cell (SVC) was roughly 3/4 that of the large vesicle cell (LVC). Furthermore there were significant differences between SVC and LVC in volume densities of vesicles extensions typical of the Type I cells were more common for LVC than for SVC. The majority of the nerve-endings observed terminated on LVC. The significance of these differences has yet to be determined.