Background: Apical tubules (ATs) in marginal cells (MCs) of the stria vascularis appear in limited stages of differentiation of the MCs, but their origin and roles remain uncertain. The present study was designed to solve the problem of whether the ATs are intracellular compartments derived from the Golgi apparatus (GA).
Methods: The cochleae of Wistar rats at ages of postnatal days 1, 3, and 5 were prepared for electron microscopy and cytochemistry using thiamine pyrophosphatase (TPPase) and coenzyme A phosphatase (CoA-Pase) as marker enzymes of trans Golgi cisterns and fluorescent labelled lectin, griffonia simplicifolia agglutinin-I (GS-1).
Results: The ATs appeared in the apical cytoplasm of the MCs between postnatal days 1 and 5. Reaction products of TPPase and CoA-Pase activities were localized in the trans-Golgi cisterns and the ATs, which were occasionally in a close apposition to the GA. The reaction was found along the apical plasma membrane of the MCs only in case of TPPase. Heavy reactions to GS-1 were seen in the supranuclear region as well as along the apical plasma membrane of the MCs.
Conclusions: The present ultrastructural and cytochemical studies indicate that the ATs, which appear in the MCs at limited perinatal stages, originate from the trans-Golgi cisterns. These ATs may be involved in the apical plasma membrane supply for the differentiation of the MCs prior to the generation of EP.