Characterization of the 1,25-dihydroxycholecalciferol-stimulated calcium influx pathway in CaCo-2 cells |
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Authors: | Xiao-Ying Tien Christopher Katnik Bahaa M Qasawa Michael D Sitrin Deborah J Nelson Thomas A Brasitus |
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Institution: | (1) Department of Medicine, Section of Gastroenterology, 5841 S. Maryland Avenue, MC 4076, 60637 Chicago, Illinois;(2) Department of Neurology, University of Chicago, 60637 Chicago, Illinois |
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Abstract: | The present studies were conducted to investigate the mechanisms underlying the 1,25-dihydroxycholecalciferol (1,25(OH)2D3)-induced increase in intracellular Ca2+ (Ca2+]
i
) in individual CaCo-2 cells. In the presence of 2mm Ca2+, 1,25(OH)2D3-induced a rapid transient rise in Ca2+]
i
in Fura-2-loaded cells in a concentration-dependent manner, which decreased, but did not return to baseline levels. In Ca2+-free buffer, this hormone still induced a transient rise in Ca2+]
i
, although of lower magnitude, but Ca2+]
i
then subsequently fell to baseline. In addition, 1,25(OH)2D3 also rapidly induced45Ca uptake by these cells, indicating that the sustained rise in Ca2+]
i
was due to Ca2+ entry. In Mn2+-containing solutions, 1,25(OH)2D3 increased the rate of Mn2+ influx which was temporally preceded by an increase in Ca2+]
i
. The sustained rise in Ca2+]
i
was inhibited in the presence of external La3+ (0.5mm). 1,25(OH)2D3 did not increase Ba2+ entry into the cells. Moreover, neither high external K+ (75mm), nor the addition of Bay K 8644 (1 μm), an L-type, voltage-dependent Ca2+ channel agonist, alone or in combination, were found to increase Ca2+]
i
, 1,25(OH)2D3 did, however, increase intracellular Na+ in the absence, but not in the presence of 2mm Ca2+, as assessed by the sodium-sensitive dye, sodium-binding benzofuran isophthalate. These data, therefore, indicate that CaCo-2
cells do not express L-type, voltage-dependent Ca2+ channels. 1,25(OH)2D3 does appear to activate a La3+-inhibitable, cation influx pathway in CaCo-2 cells. |
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Keywords: | Microfluorimetry Fura-2 Intracellular Ca2+ Intracellular Na+ Ca2+ channels |
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