Abstract
The intracellular localization of calcium in the mucosal lining of the small intestine of normal, rachitic, and Vitamin D2 treated rats was studied using45Ca-autoradiography, microincineration, and electron microscopy.
Small, electron-dense granules and autoradiographic label were seen primarily within microvilli and mitochondria. The granules were sparse in mitochondria from rachitic rats while normal rat mitochondria demonstrated them regularly. The mitochondria of Vitamin-D2-treated rats contained numerous electron dense granules. These granules remained following microincineration. An inverse relation in the amount of granules appearing in the mitochondria and in the microvillus was found. Granules were limited to the microvillus region in the rachitic animals and increased significantly in the mitochondria following treatment with Vitamin D2. This study indicates that a large amount of calcium is absorbed across the cell membrane and is then bound within the microvillus. Vitamin D is apparently necessary for mobilizing this bound calcium from the microvilli. The mobilized calcium enters the mitochondria or passes through the cell to the adjacent blood vessels.
Résumé
La mise en évidence intracellulaire du calcium au niveau du revêtement muqueux de l'intestin grêle de rats normaux, rachitiques et traités à la vitamine D2 est réalisée à l'aide de l'auto radiographie au45Ca, de la micro-incinération et de la microscopie électronique.
De petits granules denses aux électrons et le marquage autoradiographique sont visibles surtout dans les microvillosités et les mitochondries. Les granules sont rares dans les mitochondries des rats rachitiques, alors que les mitochondries du rat normal en sont toujours pourvues. Les mitochondries des rats, traités à la vitamine D2, contiennent de nombreux granules denses. Ces granules subsistent après micro-incinération. Un rapport inverse est noté dans le nombre des granules présents dans les mitochondries et les microvillosités. Les granules sont limités aux microvillosités chez les animaux rachitiques, et ils augmentent significativement dans les mitochondries après traitement à la vitamine D2. Cette étude indique qu'une quantité importante de calcium est absorbée à travers la membrane cellulaire et ce calcium se lie aux microvillosités. La vitamine D semble nécessaire pour mobiliser le calcium lié aux microvillosités. Ce calcium pénètre dans les mitochondries et traverse la cellule pour aller vers les vaisseaux sanguins adjacents.
Zusammenfassung
Die intrazelluläre Lokalisation von Calcium in der Mucosa des Dünndarms von normalen, rachitischen und Vitamin D2-behandelten Ratten wurde anhand von45Ca-Autoradiographie, Microveraschung und Elektronenmikroskopie untersucht.
Kleine elektronenundurchlässige Granula und autoradiographische Markierung wurden vorerst innerhalb der Microvilli und Mitochondrien festgestellt. Es fanden sich spärlich Granula in den Mitochondrien rachitischer Ratten, während sie in denjenigen von normalen Ratten regelmäßig vorlagen. Die Mitochondrien der Vitamin D2-behandelten Ratten enthielten zahlreiche elektronenundurchlässige Granula. Diese Granula waren auch nach Mikroveraschung noch vorhanden. Die Anzahl der Granula in den Mitochondrien und in den Microvilli standen in einem umgekehrten Verhältnis zueinander. Die Granula waren bei rachitischen Tieren auf die Microvillus-Region beschränkt und stiegen in den Mitochondrien nach Vitamin D2-Behandlung signifikant an. Diese Untersuchung zeigt, daß eine große Calciummenge durch die Zellmembran absorbiert und dann innerhalb des Microvillus gebunden wird. Es scheint, daß Vitamin D für die Freisetzung dieses gebundenen Calciums aus den Microvilli notwendig ist. Das freigesetzte Calcium tritt in die Mitochondrien ein oder wandert durch die Zelle zu den anliegenden Blutgefäßen.
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This work was supported in part by NIH grants, numbers AM-09,632 and DE-224-01.
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Sampson, H.W., Matthews, J.L., Martin, J.H. et al. An electron microscopic localization of calcium in the small intestine of normal, rachitic, and vitamin-D-treated rats. Calc. Tis Res. 5, 305–316 (1970). https://doi.org/10.1007/BF02017560
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DOI: https://doi.org/10.1007/BF02017560