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. 2023 Feb;242(2):146-152.
doi: 10.1111/joa.13775. Epub 2022 Sep 29.

Melatonin ultrastructural localization in mitochondria of human salivary glands

Raffaella Isola  1 , Ylenia Lai  1 , Roberta Noli  1 , Carla Masala  2 , Michela Isola  1 , Francesco Loy  1
Affiliations

Melatonin ultrastructural localization in mitochondria of human salivary glands

Raffaella Isola et al. J Anat. 2023 Feb.

Abstract

The hormone melatonin was initially believed to be synthesized exclusively by the pineal gland and the enterochromaffin cells, but nowadays its production and distribution were observed in several other tissues and organs. Among others, the ultrastructural localization of melatonin and its receptors has been reported in human salivary glands. In these glands, the fine localization of melatonin in intracellular organelles, above all in mitochondria, remains to be explored comprehensively. Bioptic samples of parotid and submandibular glands were treated to search for melatonin using the immunogold staining method by transmission electron microscopy. Morphometric analysis was applied to micrographs. The results indicated that, both in parotid and submandibular glands mitochondria, a certain melatonin positivity was present. Within glandular cells, melatonin was less retrieved in mitochondria than in secretory granules; however, its presence in this organelle was clearly evident. Inside striated duct cells, melatonin staining in mitochondria was more prominent than in glandular cells. Our data provide an ultrastructural report on the presence of melatonin in mitochondria of human major salivary glands and represent a fundamental prerequisite for a better understanding of the melatonin role in this organelle.

Keywords: immunogold method; melatonin; mitochondria; salivary glands.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

FIGURE 1
FIGURE 1
Melatonin localization in granules of serous cells in human parotid (a) and submandibular (b) glands. The melatonin localization in mitochondria (arrow) and in rough endoplasmic reticulum (arrowheads) is indicated. N: Nuclei. Bars: 1 μm.
FIGURE 2
FIGURE 2
Submandibular gland. Serous cells show melatonin localization in the granules (G), in the rough endoplasmic reticulum (black arrowhead) and nuclei (N; white arrowheads). Note that mitochondria (m) show reactivity for the hormone (black arrows). a, b, c: Bars 500 nm.
FIGURE 3
FIGURE 3
Parotid gland. Melatonin reactivity (arrows) in mitochondria (m) of acinar cells and in the nucleus (N; arrowheads). G, granules. Bar: 1 μm.
FIGURE 4
FIGURE 4
TEM. Parotid glands. High magnification of mitochondria (m), labeled for melatonin detection (arrows). These organelles showed reactivity for melatonin in their central part (a) or at their periphery (b). (a, b) Bars 250 nm.
FIGURE 5
FIGURE 5
Striated ductal cells. (a) Submandibular gland. (b) Parotid gland. Melatonin localization (black arrows) was evident. Arrowheads: Nuclear localization. M: Mitochondria. N: Nuclei. Bars 1 μm.
See this image and copyright information in PMC

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