Rapid modulation of Ca2+ uptake in human jejunal enterocytes.
The active metabolite of D vitamin, 1,25(OH)2D3, has been suggested to promote acute uptake of calcium through the intestinal lining in cell lines and murine models. In this study, the effects of D vitamin on the cytoplasmic Ca2+ of single human jejunal enterocytes, obtained with LOC-I-GUT technique, was analyzed in vivo in a fluorometric system using fura-2 as the Ca2+-sensing probe. Vitamin-promoted acute Ca2+ influx exhibited dual kinetics, indicating initial release from intracellular Ca2+ pools and fast entry from the extracellular space. Furthermore, providing a chemical clamp of membrane potential close to 0 mV did not activate voltage-sensitive calcium channels in the cellular membrane, neither was the hormone-induced Ca2+ influx affected by verapamil. This advocates that voltage-operated channels like L-type Ca2+ channels do not participate in the process of Ca2+ uptake. In fact, the existence of calcium-release-activated-calcium channels (I(CRAC)) was implied by the findings that irreversible depletion of intracellular Ca2+ stores by thapsigargin promoted Ca2+ entry. In the thapsigargin-treated enterocytes, D vitamin lost its ability to promote calcium entry indicating an important role for intracellular store-operated Ca2+ stores in the acute effects of 1,25(OH)2D3.
Forsell
P
P
University of Uppsala, Department of Surgical Sciences and Department of Pharmacy, Uppsala, Sweden.
Eberhardson
M
M
Lennernas
H
H
Knutson
T
T
Knutson
L
L
D000328:Adult; D000704:Analysis of Variance; D002118:Calcium / Q000378:metabolism* / Q000493:pharmacokinetics; D015220:Calcium Channels / Q000737:chemistry; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism; D020895:Enterocytes / Q000378:metabolism*; D005260:Female; D005470:Fluorometry; D006801:Humans; D007413:Intestinal Mucosa / Q000378:metabolism; D007583:Jejunum / Q000166:cytology* / Q000378:metabolism; D007700:Kinetics; D008297:Male; D008564:Membrane Potentials; D008953:Models, Anatomic; D015233:Models, Statistical; D010024:Osteoporosis / Q000378:metabolism; D013696:Temperature; D019284:Thapsigargin / Q000378:metabolism / Q000494:pharmacology; D013997:Time Factors; D014807:Vitamin D / Q000378:metabolism
D015220:Calcium Channels; D014807:Vitamin D; D019284:Thapsigargin; D002118:Calcium