Novel choline transport characteristics in Caco-2 cells.
Choline transport is characterized by sodium-dependent high-affinity, sodium-independent low-affinity, and sodium-independent blood-brain barrier transport mechanisms. Each defined mechanism has specific characteristics with regard to affinity for choline, transport capacity, and inhibition by hemicholinium. The purpose of this study is to determine the characteristics of choline transport across Caco-2 monolayers.


METHODS
Choline transport across Caco-2 cell monolayers was determined in both the apical to basal direction and the opposite direction. Further, the determination of calcium dependence and specific inhibitors was made. Determination of the apparent permeability of choline was calculated by established methods.


RESULTS
The apical to basal Caco-2 permeability coefficient is 11.11 +/- 0.33 x 10(-6) cm/sec with 21.3% of the choline associating with the cells. Meanwhile the basal to apical value is approximately 50% less (5.55 +/- 0.14 x 10(-6) cm/sec), suggesting an active apical to basal transport mechanism. Choline transport in this system was inhibited by nifedipine (82%), verapamil (80%), EGTA (36%), and cyclosporin (15%).


CONCLUSIONS
Choline transport across Caco-2 cells is demonstrated to be active and both pH- and Ca(2+)-dependent. Furthermore, choline transport across Caco-2 monolayers has unique characteristics when compared to traditional choline transport models.
Crowe
A P
AP
Division of Health Sciences, School of Pharmacy, Curtin University of Technology, Perth, Western Australia 6845.
Lockman
P R
PR
Abbruscato
T J
TJ
Allen
D D
DD
D001692:Biological Transport; D018938:Caco-2 Cells; D002794:Choline / Q000378:metabolism*; D004347:Drug Interactions; D006801:Humans; D006863:Hydrogen-Ion Concentration; D026901:Membrane Transport Proteins / Q000187:drug effects; D009543:Nifedipine / Q000494:pharmacology; D014700:Verapamil / Q000494:pharmacology
D026901:Membrane Transport Proteins; C065637:choline transporter; D014700:Verapamil; D009543:Nifedipine; D002794:Choline