Insulin and IGF-I inhibit calcium-dependent chloride secretion by T84 human colonic epithelial cells

Abstract

D-Myo-inositol (3,4,5,6) tetrakisphosphate [Ins(3,4,5,6)P(4)] or phosphatidylinositol 3-kinase (PI 3-kinase) activity acts to inhibit calcium-dependent chloride secretion in T84 colonic epithelial cells. To further distinguish between the contributions of these two signaling pathways to the inhibition of secretion, we studied effects of insulin, because the insulin receptor links to PI 3-kinase but not to pathways postulated to generate Ins(3,4,5,6)P(4). Chloride secretion across T84 cell monolayers was studied in Ussing chambers. Activation of PI 3-kinase was assessed by Western blotting. Basolateral, but not apical, addition of insulin inhibited carbachol- and thapsigargin-induced chloride secretion in a time- and concentration-dependent fashion. Insulin-like growth factor-I (IGF-I) had similar effects. Insulin had no effect on Ins(3,4,5,6)P(4) levels, and the inhibitory effects of insulin and IGF-I on chloride secretion were fully reversed by the PI 3-kinase inhibitors wortmannin and LY-294002. Western blot analysis showed that both insulin and IGF-I recruited the 85-kDa regulatory and 110-kDa catalytic subunits of PI 3-kinase to anti-phosphotyrosine immunoprecipitates. In conclusion, insulin and IGF-I act to inhibit calcium-dependent chloride secretion through a PI 3-kinase-dependent pathway. Because insulin is released in a pulsatile fashion postprandially and IGF-I levels are elevated in pathological settings, our findings may have physiological and/or pathophysiological significance.

TGF-β effects on epithelial ion transport and barrier: reduced Cl− secretion blocked by a p38 MAPK inhibitor

“…The effects of recombinant TGF-␤ were reproduced in epithelia infected with adenovirus encoding the gene for the active form of TGF-␤; diminished ⌬I sc to forskolin were apparent 144 h postinfection (i.e., end of the experiment). However, unlike other growth factors, such as EGF and IGF, which induce acute effects on epithelial ⌬I sc (39,11), TGF-␤ when added to T84 monolayers in Ussing chambers for 30 min had no effect on subsequent forskolin-evoked ⌬I sc . Thus TGF-␤ can be added to the list of cytokines that directly modulate epithelial ion transport (reviewed in Ref.…”

Ileal apical Na+-dependent bile acid transporter ASBT is upregulated in rats with diabetes mellitus induced by low doses of streptozotocin

“…In this regard, the role of insulin in the regulation of a number of intestinal epithelial processes is well established. For example, insulin has been shown to stimulate the function of oligopeptide transporter, Pept-1 (36), to decrease the transepithelial resistance (28), and to abrogate calcium-dependent chloride secretion in T84 intestinal epithelial cells (8). Additionally, previous studies have shown that insulin acutely decreased glucose flux across rat jejunum and ileum (27).…”

Gs Protein-coupled Receptor Agonists Induce Transactivation of the Epidermal Growth Factor Receptor in T84 Cells

“…In addition to G q PCR agonists (3, 8 -10), a wide array of substances, including bile acids (11), bacteria (12)(13)(14), steroids (15), and growth factors (16,17), have all been shown to have the capability to transactivate the EGFr and thereby recruit associated effector signaling pathways. However, as yet, there is little information regarding the role of EGFr-dependent signaling mechanisms in regulating cellular responses to agonists that bind to G s PCRs thereby eliciting elevations in intracellular cAMP.…”