Kinetic studies of calcium movements in intestinal cells: Effects of vitamin D deficiency and treatment

Summary

The calcium distribution among three cellular calcium pools was studied by kinetic analyses in intestinal cells isolated from normal, vitamin D-deficient and vitamin D-repleted chicks. Vitamin D deficiency significantly reduces the cellular⁴⁵Ca uptake by reducing the intracellular exchangeable calcium pool. Calcium efflux from the cells varies depending on the onset of the vitamin D deficiency: at four weeks calcium efflux is greater than control but after the fifth week it decreases and remains significantly lower than control. The cytoplasmic calcium pool follows the same biphasic pattern: it is higher at 4 weeks and lower after 5 weeks of D-deficiency. The mitochondrial calcium pool and calcium efflux from this compartment do not show a biphasic pattern. They are markedly depressed from the 4th week of D-deficiency. Eighteen hours after vitamin D administration the cytoplasmic and mitochondrial calcium pools return toward normal; after 42 hours the cytoplasmic pool and calcium efflux from the cell are normal. These data suggest that in D-deficiency, mitochondrial calcium uptake is depressed producing first a rise and then a drop in cytoplasmic calcium. The cytoplasmic calcium is responsible for the changes in cellular calcium efflux. The decreased calcium uptake may be partially due to a decreased cellular exchangeable calcium pool.