Transport of thiamine in human intestine: mechanism and regulation in intestinal epithelial cell model Caco-2.
The present study examined the intestinal uptake of thiamine (vitamin B(1)) using the human-derived intestinal epithelial cells Caco-2 as an in vitro model system. Thiamine uptake was found to be 1) temperature and energy dependent and occurred with minimal metabolic alteration; 2) pH sensitive; 3) Na(+) independent; 4) saturable as a function of concentration with an apparent Michaelis-Menten constant of 3.18 +/- 0.56 microM and maximal velocity of 13.37 +/- 0.94 pmol. mg protein(-1). 3 min(-1); 5) inhibited by the thiamine structural analogs amprolium and oxythiamine, but not by unrelated organic cations tetraethylammonium, N-methylnicotinamide, and choline; and 6) inhibited in a competitive manner by amiloride with an inhibition constant of 0.2 mM. The role of specific protein kinase-mediated pathways in the regulation of thiamine uptake by Caco-2 cells was also examined using specific modulators of these pathways. The results showed possible involvement of a Ca(2+)/calmodulin (CaM)-mediated pathway in the regulation of thiamine uptake. No role for protein kinase C- and protein tyrosine kinase-mediated pathways in the regulation of thiamine uptake was evident. These results demonstrate the involvement of a carrier-mediated system for thiamine uptake by Caco-2 intestinal epithelial cells. This system is Na(+) independent and is different from the transport systems of organic cations. Furthermore, a CaM-mediated pathway appears to play a role in regulating thiamine uptake in these cells.
Said
H M
HM
Veterans Affairs Medical Center, Long Beach, California, 90822, USA. hmsaid@uc.edu
Ortiz
A
A
Kumar
C K
CK
Chatterjee
N
N
Dudeja
P K
PK
Rubin
S
S
D001692:Biological Transport / Q000502:physiology; D018938:Caco-2 Cells; D002412:Cations / Q000494:pharmacology; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007413:Intestinal Mucosa / Q000166:cytology / Q000378:metabolism*; D009994:Osmolar Concentration; D011494:Protein Kinases / Q000502:physiology; D012964:Sodium / Q000378:metabolism; D013696:Temperature; D013831:Thiamine / Q000031:analogs & derivatives / Q000037:antagonists & inhibitors / Q000378:metabolism*; D013997:Time Factors
D002412:Cations; D012964:Sodium; D011494:Protein Kinases; D013831:Thiamine