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transport
Departments of 1 Physiology and Biophysics and 2 Pediatrics, University of Illinois at Chicago, Chicago, Illinois 60612-7342
Taurodeoxycholic acid (TDC) stimulates Cl
transport in
adult (AD), but not weanling (WN) and newborn (NB), rabbit colonic epithelial cells (colonocytes). The present study demonstrates that
stimuli like neurotensin (NT) are also age specific and identifies the
age-dependent signaling step. Bile acid actions are segment and bile
acid specific. Thus although TDC and taurochenodeoxycholate stimulate
Cl
transport in AD distal but not proximal colon,
taurocholate has no effect in either segment. TDC increases
intracellular Ca2+ concentration
([Ca2+]i) in AD, but not in WN and NB,
colonocytes. In AD cells, TDC (5 min) action on Cl
transport needs intra- but not extracellular Ca2+. NT,
histamine, and bethanechol increase Cl
transport and
[Ca2+]i in AD, but not WN, distal
colonocytes. However, A-23187 increased [Ca2+]i and Cl
transport in all
age groups, suggesting that Ca2+-sensitive Cl
transport is present from birth. Study of the proximal steps in
Ca2+ signaling revealed that NT, but not TDC, activates a
GTP-binding protein, G
q, in AD and WN cells. In
addition, although WN and AD colonocytes had similar levels of
phosphatidylinositol 4,5-bisphosphate, NT and TDC increased
1,4,5-inositol trisphosphate content only in AD cells.
Nonresponsiveness of WN cells to Ca2+-dependent stimuli,
therefore, is due to the absence of measurable phospholipase C
activity. Thus delays in Ca2+ signaling afford a crucial
protective mechanism to meet the changing demands of the developing colon.
taurodeoxycholic acid; neurohumoral modulators; rabbit colon; inositol trisphosphates
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