Co-existence of tyrosine hydroxylase and dopamine beta-hydroxylase immunoreactivity in glomus cells of the cat carotid body.

Catecholamines are thought to play an important role in sensory transduction in the arterial chemoreceptors of the mammalian carotid body, and classical cytochemical techniques have demonstrated their presence in the type I (glomus) cells of this organ. However, it remains controversial whether dopamine (DA) and norepinephrine (NE) occur in the same or in different subtypes of glomus cells. In the present study, we have addressed this issue using immunocytochemistry to compare the localization of tyrosine hydroxylase (TH) and dopamine beta-hydroxylase (D beta H) in the cat carotid body. Both pre- and post-embedding double-labelling immunohistochemical techniques were employed. TH and D beta H were found to co-exist in over 90% of the glomus cells, and they were co-localized at equivalent levels in almost 80% of the cells; less than 5% contained only TH. The results suggest that DA and NE are synthesized and stored in a common cell population in the cat carotid body.