Mitochondrial localization of melatonin in salivary glands: ultrastructural evidences

Abstract

The storage of melatonin in acinar secretory granules of human salivary glands and the release of the hormone by granule exocytosis following the regulated secretory pathway were recently reported [1-4]. Melatonin was detected principally in secretory granules, but also in small vesicles, rough endoplasmic reticulum and in the nucleus of the cells. Recently, the occur- rence of melatonin has been reported in mitochondria [5] as a peculiar site of its function, but the ultrastructural demonstration of melatonin localization in these organelles has not been delved deeper. In this study we showed the fine localization of this hormone in mitochondria by transmission electron microscopy. Bioptic samples of human parotid, submandibular and labial glands were fixed, dehydrated, embedded in Epon Resin and processed to demonstrate melatonin reactivity by the immunogold staining method. In each type of major and minor human salivary glands, the melatonin reactivity was detected in the mitochondrial membranes in secretory cells. Moreover, melatonin was found in mitochondria of ductal cells. Our data pro- vided new morphological evidences of the melatonin localization in mitochondria, fundamental prerequisite for a better understanding the roles of melatonin in human secretory cells.

Melatonin