ULTRASTRUCTURAL-LOCALIZATION OF AMILORIDE-SENSITIVE SODIUM-CHANNELS AND NA-ATPASE IN THE RATS OLFACTORY EPITHELIAL SURFACE(,K+)

Several studies have indicated that olfactory responses are impeded by amiloride. Therefore, it was of interest to see whether, and if so wh ich, olfactory epithelial cellular compartments have amiloride-sensiti ve structures. Using ultrastructural methods that involved rapid freez ing, freeze-substitution and low temperature embedding of olfactory ep ithelia, this study shows that, in the rat, this tissue is immunoreact ive to antibodies against amiloride sensitive Na+-channels. However, m icrovilli of olfactory supporting cells, as opposed to receptor cilia, contained most of the immunoreactive sites. Apices from which the mic rovilli sprout and receptor cell dendritic knobs had much less if any of the amiloride-antibody binding sites. Using a direct ligand-binding cytochemical method, this study also confirms earlier ones that showe d that olfactory receptor cell cilia have Na+,K+-ATPase. It is propose d that supporting cell microvilli and the receptor cilia themselves ha ve mechanisms, different but likely complementary, that participate in regulating ti-ie salt concentration around the receptor cell cilia. i n this way, both structures help to provide the ambient mucous environ ment for receptor cells to function properly This regulation of the sa lt concentration of an ambient fluid environment is a function that th e olfactory epithelium shares with cells of transporting epithelia, su ch as those of kidney.