Characterization of the 1,25-dihydroxycholecalciferol-stimulated calcium influx pathway in CaCo-2 cells.
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 2 mM 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 Ca(2+)-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 induced 45Ca uptake by these cells, indicating that the sustained rise in [Ca2+]i was due to Ca2+ entry. In Mn(2+)-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+ (0.5 mM). 1,25(OH)2D3 did not increase Ba2+ entry into the cells. Moreover, neither high external K+ (75 mM), nor the addition of Bay K 8644 (1 microM), 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 2 mM 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 La(3+)-inhibitable, cation influx pathway in CaCo-2 cells.
Tien
X Y
XY
Department of Neurology, University of Chicago, Illinois 60637.
Katnik
C
C
Qasawa
B M
BM
Sitrin
M D
MD
Nelson
D J
DJ
Brasitus
T A
TA
D002117:Calcitriol / Q000378:metabolism / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology*; D002132:Calcium Radioisotopes / Q000378:metabolism; D002460:Cell Line; D004553:Electric Conductivity / Q000187:drug effects; D005470:Fluorometry; D006801:Humans; D007811:Lanthanum / Q000494:pharmacology; D008345:Manganese / Q000494:pharmacology; D014407:Tumor Cells, Cultured
D015220:Calcium Channels; D002132:Calcium Radioisotopes; D008345:Manganese; D007811:Lanthanum; D002117:Calcitriol; D002118:Calcium