Differences in Ca2+signaling underlie age-specific effects of secretagogues on colonic Cl−transport

Abstract

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+]iin AD, but not WN, distal colonocytes. However, A-23187 increased [Ca2+]iand 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, Gαq, 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.