Bile salts and ileal calcium transport in rats: a neglected factor in intestinal calcium absorption.
Ileum displays little active transcellular calcium (Ca2+) absorption but is credited with the bulk of Ca2+ absorbed in vivo. We examined the effect of taurodeoxycholic acid (TDC, 2 mM), a bile salt, on mannitol (MN, a marker of intercellular solute traffic) and Ca2+ fluxes in rat ileum. In the absence of electrochemical gradients between the mucosal (M) and serosal (S) bathing media in an Ussing chamber, net flux (Jnet) was observed in the S-to-M direction for both MN and Ca2+, i.e., the unidirectional secretory S-to-M flux (Js-->m) exceeded the absorptive M-to-S flux (Jm-->s). Mucosal TDC caused simultaneous increase in transepithelial conductance and Js-->m for both MN and Ca2+. This was followed by even greater increases in MN and Ca2+ Jm-->s, so that ultimately Jm-->s equaled Js-->m in each case. In control tissue, Js-->m for Ca2+ appeared to permeate exclusively through the intercellular MN pathway while part of Jm-->s for Ca2+ appeared to traverse through a non-MN route. After the TDC-induced increase in intercellular solute permeability, both Ca2+ fluxes appeared to traverse through the aqueous MN conduit. During the postprandial state, the presence of bile salts and the relative abundance of Ca2+ in ileal lumen can cause bulk Ca2+ absorption through the intercellular pathway.
Hu
M S
MS
Medical Service, Veterans Health Affairs Medical Center, Sepulveda 91343.
Kayne
L H
LH
Willsey
P A
PA
Koteva
A B
AB
Jamgotchian
N
N
Lee
D B
DB
D000042:Absorption / Q000187:drug effects; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002118:Calcium / Q000378:metabolism*; D004594:Electrophysiology; D007082:Ileum / Q000378:metabolism* / Q000502:physiology; D007413:Intestinal Mucosa / Q000378:metabolism* / Q000502:physiology; D008297:Male; D008353:Mannitol / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D013657:Taurodeoxycholic Acid / Q000494:pharmacology*
D008353:Mannitol; D013657:Taurodeoxycholic Acid; D002118:Calcium