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Physiological concentrations of bile acids down-regulate agonist induced secretion in colonic epithelial cells.

Keating N, Mroz MS, Scharl MM, Marsh C, Ferguson G, Hofmann AF, Keely SJ - J. Cell. Mol. Med. (2009)

Bottom Line: At high concentrations (0.5-1 mM), DCA acutely stimulated Cl(-) secretion but this effect was associated with cell injury, as evidenced by decreased transepithelial resistance (TER) and increased lactate dehydrogenase (LDH) release.The EGFr inhibitor, AG1478, and the protein synthesis inhibitor, cycloheximide, reversed the antisecretory effects of DCA, while the MAPK inhibitors, PD98059 and SB203580, did not.In summary, our studies suggest that, in contrast to its acute prosecretory effects at pathophysiological concentrations, lower, physiologically relevant, levels of DCA chronically down-regulate colonic epithelial secretory function.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular Medicine, Royal College of Surgeons in Ireland, Dublin, Ireland.

ABSTRACT
In patients with bile acid malabsorption, high concentrations of bile acids enter the colon and stimulate Cl(-) and fluid secretion, thereby causing diarrhoea. However, deoxycholic acid (DCA), the predominant colonic bile acid, is normally present at lower concentrations where its role in regulating transport is unclear. Thus, the current study set out to investigate the effects of physiologically relevant DCA concentrations on colonic epithelial secretory function. Cl(-) secretion was measured as changes in short-circuit current across voltage-clamped T(84) cell monolayers. At high concentrations (0.5-1 mM), DCA acutely stimulated Cl(-) secretion but this effect was associated with cell injury, as evidenced by decreased transepithelial resistance (TER) and increased lactate dehydrogenase (LDH) release. In contrast, chronic (24 hrs) exposure to lower DCA concentrations (10-200 microM) inhibited responses to Ca(2+) and cAMP-dependent secretagogues without altering TER, LDH release, or secretagogue-induced increases in intracellular second messengers. Other bile acids - taurodeoxycholic acid, chenodeoxycholic acid and cholic acid - had similar antisecretory effects. DCA (50 microM) rapidly stimulated phosphorylation of the epidermal growth factor receptor (EGFr) and both ERK and p38 MAPKs (mitogen-activated protein kinases). The EGFr inhibitor, AG1478, and the protein synthesis inhibitor, cycloheximide, reversed the antisecretory effects of DCA, while the MAPK inhibitors, PD98059 and SB203580, did not. In summary, our studies suggest that, in contrast to its acute prosecretory effects at pathophysiological concentrations, lower, physiologically relevant, levels of DCA chronically down-regulate colonic epithelial secretory function. On the basis of these data, we propose a novel role for bile acids as physiological regulators of colonic secretory capacity.

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Prolonged exposure to physiological concentrations of DCA inhibits Cl− secretion across rat colon. (A) Voltage‐clamped segments of stripped rat colonic mucosa were apically exposed to DCA (1 mM) and Isc responses were recorded (n= 5). (B) Voltage‐clamped sections of rat colon were exposed to increasing concentrations of apical DCA and maximal Isc responses were measured (n= 4–7 for each concentration tested). (C) Voltage‐clamped rat colonic mucosa was exposed to 200 μM apical DCA and after 3 hrs incubation subsequent Isc responses to CCh (100 μM; n= 4) and FSK (10 μM; n= 5) were measured. ***P < 0.005 when compared to control cells.
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f3: Prolonged exposure to physiological concentrations of DCA inhibits Cl− secretion across rat colon. (A) Voltage‐clamped segments of stripped rat colonic mucosa were apically exposed to DCA (1 mM) and Isc responses were recorded (n= 5). (B) Voltage‐clamped sections of rat colon were exposed to increasing concentrations of apical DCA and maximal Isc responses were measured (n= 4–7 for each concentration tested). (C) Voltage‐clamped rat colonic mucosa was exposed to 200 μM apical DCA and after 3 hrs incubation subsequent Isc responses to CCh (100 μM; n= 4) and FSK (10 μM; n= 5) were measured. ***P < 0.005 when compared to control cells.

Mentions: We next analysed DCA effects on Cl− secretion across sections of rat colon. In these experiments DCA was added apically in order to more closely mimic in vivo situations where bile acids are found in the lumen. As expected, high concentrations of DCA (1 mM) stimulated a rapid and transient ΔIsc response (Fig. 3A). The effects of DCA were concentration‐dependent with levels more than 200 μM being required for a prosecretory effect to occur (Fig. 3B). However, when tissues were exposed to relatively low concentrations of DCA (200 μM) on the apical side for prolonged periods (3 hrs), subsequent secretory responses to CCh (100 μM) or FSK (10 μM) were significantly attenuated (Fig. 3C). This effect of DCA was not associated with alterations in tissue viability or integrity as indicated by transmucosal conductance measurements. The conductance across control tissues was 26.5 ± 1.8 mS/cm2 compared to 29.7 ± 3.7 mS/cm2 in DCA‐pretreated tissues (n= 5). Thus, similar to its effects in cultured human colonic epithelia, prolonged exposure to relatively low concentrations of DCA exerts antisecretory effects in rat colonic mucosa.


Physiological concentrations of bile acids down-regulate agonist induced secretion in colonic epithelial cells.

Keating N, Mroz MS, Scharl MM, Marsh C, Ferguson G, Hofmann AF, Keely SJ - J. Cell. Mol. Med. (2009)

Prolonged exposure to physiological concentrations of DCA inhibits Cl− secretion across rat colon. (A) Voltage‐clamped segments of stripped rat colonic mucosa were apically exposed to DCA (1 mM) and Isc responses were recorded (n= 5). (B) Voltage‐clamped sections of rat colon were exposed to increasing concentrations of apical DCA and maximal Isc responses were measured (n= 4–7 for each concentration tested). (C) Voltage‐clamped rat colonic mucosa was exposed to 200 μM apical DCA and after 3 hrs incubation subsequent Isc responses to CCh (100 μM; n= 4) and FSK (10 μM; n= 5) were measured. ***P < 0.005 when compared to control cells.
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Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC4940785&req=5

f3: Prolonged exposure to physiological concentrations of DCA inhibits Cl− secretion across rat colon. (A) Voltage‐clamped segments of stripped rat colonic mucosa were apically exposed to DCA (1 mM) and Isc responses were recorded (n= 5). (B) Voltage‐clamped sections of rat colon were exposed to increasing concentrations of apical DCA and maximal Isc responses were measured (n= 4–7 for each concentration tested). (C) Voltage‐clamped rat colonic mucosa was exposed to 200 μM apical DCA and after 3 hrs incubation subsequent Isc responses to CCh (100 μM; n= 4) and FSK (10 μM; n= 5) were measured. ***P < 0.005 when compared to control cells.
Mentions: We next analysed DCA effects on Cl− secretion across sections of rat colon. In these experiments DCA was added apically in order to more closely mimic in vivo situations where bile acids are found in the lumen. As expected, high concentrations of DCA (1 mM) stimulated a rapid and transient ΔIsc response (Fig. 3A). The effects of DCA were concentration‐dependent with levels more than 200 μM being required for a prosecretory effect to occur (Fig. 3B). However, when tissues were exposed to relatively low concentrations of DCA (200 μM) on the apical side for prolonged periods (3 hrs), subsequent secretory responses to CCh (100 μM) or FSK (10 μM) were significantly attenuated (Fig. 3C). This effect of DCA was not associated with alterations in tissue viability or integrity as indicated by transmucosal conductance measurements. The conductance across control tissues was 26.5 ± 1.8 mS/cm2 compared to 29.7 ± 3.7 mS/cm2 in DCA‐pretreated tissues (n= 5). Thus, similar to its effects in cultured human colonic epithelia, prolonged exposure to relatively low concentrations of DCA exerts antisecretory effects in rat colonic mucosa.

Bottom Line: At high concentrations (0.5-1 mM), DCA acutely stimulated Cl(-) secretion but this effect was associated with cell injury, as evidenced by decreased transepithelial resistance (TER) and increased lactate dehydrogenase (LDH) release.The EGFr inhibitor, AG1478, and the protein synthesis inhibitor, cycloheximide, reversed the antisecretory effects of DCA, while the MAPK inhibitors, PD98059 and SB203580, did not.In summary, our studies suggest that, in contrast to its acute prosecretory effects at pathophysiological concentrations, lower, physiologically relevant, levels of DCA chronically down-regulate colonic epithelial secretory function.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular Medicine, Royal College of Surgeons in Ireland, Dublin, Ireland.

ABSTRACT
In patients with bile acid malabsorption, high concentrations of bile acids enter the colon and stimulate Cl(-) and fluid secretion, thereby causing diarrhoea. However, deoxycholic acid (DCA), the predominant colonic bile acid, is normally present at lower concentrations where its role in regulating transport is unclear. Thus, the current study set out to investigate the effects of physiologically relevant DCA concentrations on colonic epithelial secretory function. Cl(-) secretion was measured as changes in short-circuit current across voltage-clamped T(84) cell monolayers. At high concentrations (0.5-1 mM), DCA acutely stimulated Cl(-) secretion but this effect was associated with cell injury, as evidenced by decreased transepithelial resistance (TER) and increased lactate dehydrogenase (LDH) release. In contrast, chronic (24 hrs) exposure to lower DCA concentrations (10-200 microM) inhibited responses to Ca(2+) and cAMP-dependent secretagogues without altering TER, LDH release, or secretagogue-induced increases in intracellular second messengers. Other bile acids - taurodeoxycholic acid, chenodeoxycholic acid and cholic acid - had similar antisecretory effects. DCA (50 microM) rapidly stimulated phosphorylation of the epidermal growth factor receptor (EGFr) and both ERK and p38 MAPKs (mitogen-activated protein kinases). The EGFr inhibitor, AG1478, and the protein synthesis inhibitor, cycloheximide, reversed the antisecretory effects of DCA, while the MAPK inhibitors, PD98059 and SB203580, did not. In summary, our studies suggest that, in contrast to its acute prosecretory effects at pathophysiological concentrations, lower, physiologically relevant, levels of DCA chronically down-regulate colonic epithelial secretory function. On the basis of these data, we propose a novel role for bile acids as physiological regulators of colonic secretory capacity.

Show MeSH
Related in: MedlinePlus