Secretion In Colonic Epithelia Research Articles

Genomic Priming of the Antisecretory Response to Estrogen in Rat Distal Colon throughout the Estrous Cycle

Abstract The secretion of Cl− across distal colonic crypt cells provides the driving force for the movement of fluid into the luminal space. 17β-Estradiol (E2) produces a rapid and sustained reduction in secretion in females, which is dependent on the novel protein kinase Cδ (PKCδ) isozyme and PKA isoform I targeting of KCNQ1 channels. This sexual dimorphism in the E2 response is associated with a higher expression level of PKCδ in female compared with the male tissue. The present study revealed the antisecretory response is regulated throughout the female reproductive (estrous) cycle and is primed by genomic regulation of the kinases. E2 (1–10 nm) decreased cAMP-dependent secretion in colonic epithelia during the estrous, metestrous, and diestrous stages. A weak inhibition of secretion was demonstrated in the proestrous stage. The expression levels of PKCδ and PKA fluctuated throughout the estrous cycle and correlated with the potency of the antisecretory effect of E2. The expression of PKCδ and PKA were up-regulated by estrogen at a transcriptional level via a PKCδ-MAPK-cAMP response element-binding protein-regulated pathway indicating a genomic priming of the antisecretory response. PKCδ was activated by the membrane-impermeant E2-BSA, and this response was inhibited by the estrogen receptor antagonist ICI 182,780. The 66-kDa estrogen receptor-α isoform was present at the plasma membrane of female colonic crypt cells with a lower abundance found in male colonic crypts. The study demonstrates estrogen regulation of intestinal secretion both at a rapid and transcriptional level, demonstrating an interdependent relationship between both nongenomic and genomic hormone responses.

Genomic Priming of the Antisecretory Response to Estrogen in Rat Distal Colon throughout the Estrous Cycle

The secretion of Cl(-) across distal colonic crypt cells provides the driving force for the movement of fluid into the luminal space. 17beta-Estradiol (E2) produces a rapid and sustained reduction in secretion in females, which is dependent on the novel protein kinase C delta (PKC delta) isozyme and PKA isoform I targeting of KCNQ1 channels. This sexual dimorphism in the E2 response is associated with a higher expression level of PKC delta in female compared with the male tissue. The present study revealed the antisecretory response is regulated throughout the female reproductive (estrous) cycle and is primed by genomic regulation of the kinases. E2 (1-10 nm) decreased cAMP-dependent secretion in colonic epithelia during the estrus, metestrus, and diestrus stages. A weak inhibition of secretion was demonstrated in the proestrus stage. The expression levels of PKC delta and PKA fluctuated throughout the estrous cycle and correlated with the potency of the antisecretory effect of E2. The expression of PKC delta and PKA were up-regulated by estrogen at a transcriptional level via a PKC delta-MAPK-cAMP response element-binding protein-regulated pathway indicating a genomic priming of the antisecretory response. PK Cdelta was activated by the membrane-impermeant E2-BSA, and this response was inhibited by the estrogen receptor antagonist ICI 182,780. The 66-kDa estrogen receptor-alpha isoform was present at the plasma membrane of female colonic crypt cells with a lower abundance found in male colonic crypts. The study demonstrates estrogen regulation of intestinal secretion both at a rapid and transcriptional level, demonstrating an interdependent relationship between both nongenomic and genomic hormone responses.

Genomic Priming of the Antisecretory Response to Estrogen in Rat Distal Colon throughout the Estrous Cycle

The secretion of Cl− across distal colonic crypt cells provides the driving force for the movement of fluid into the luminal space. 17β-Estradiol (E2) produces a rapid and sustained reduction in secretion in females, which is dependent on the novel protein kinase Cδ (PKCδ) isozyme and PKA isoform I targeting of KCNQ1 channels. This sexual dimorphism in the E2 response is associated with a higher expression level of PKCδ in female compared with the male tissue. The present study revealed the antisecretory response is regulated throughout the female reproductive (estrous) cycle and is primed by genomic regulation of the kinases. E2 (1-10 nm) decreased cAMP-dependent secretion in colonic epithelia during the estrous, metestrous, and diestrous stages. A weak inhibition of secretion was demonstrated in the proestrous stage. The expression levels of PKCδ and PKA fluctuated throughout the estrous cycle and correlated with the potency of the antisecretory effect of E2. The expression of PKCδ and PKA were up-regulated by estrogen at a transcriptional level via a PKCδ-MAPK-cAMP response element-binding protein-regulated pathway indicating a genomic priming of the antisecretory response. PKCδ was activated by the membrane-impermeant E2-BSA, and this response was inhibited by the estrogen receptor antagonist ICI 182,780. The 66-kDa estrogen receptor-α isoform was present at the plasma membrane of female colonic crypt cells with a lower abundance found in male colonic crypts. The study demonstrates estrogen regulation of intestinal secretion both at a rapid and transcriptional level, demonstrating an interdependent relationship between both nongenomic and genomic hormone responses.

Genomic Priming of the Antisecretory Response to Estrogen in Rat Distal Colon throughout the Estrous Cycle

ABSTRACT The secretion of Cl− across distal colonic crypt cells provides the driving force for the movement of fluid into the luminal space. 17β-Estradiol (E2) produces a rapid and sustained reduction in secretion in females, which is dependent on the novel protein kinase Cδ (PKCδ) isozyme and PKA isoform I targeting of KCNQ1 channels. This sexual dimorphism in the E2 response is associated with a higher expression level of PKCδ in female compared with the male tissue. The present study revealed the antisecretory response is regulated throughout the female reproductive (estrous) cycle and is primed by genomic regulation of the kinases. E2 (1-10 nm) decreased cAMP-dependent secretion in colonic epithelia during the estrous, metestrous, and diestrous stages. A weak inhibition of secretion was demonstrated in the proestrous stage. The expression levels of PKCδ and PKA fluctuated throughout the estrous cycle and correlated with the potency of the antisecretory effect of E2. The expression of PKCδ and PKA were up-regulated by estrogen at a transcriptional level via a PKCδ-MAPK-cAMP response element-binding protein-regulated pathway indicating a genomic priming of the antisecretory response. PKCδ was activated by the membrane-impermeant E2-BSA, and this response was inhibited by the estrogen receptor antagonist ICI 182,780. The 66-kDa estrogen receptor-α isoform was present at the plasma membrane of female colonic crypt cells with a lower abundance found in male colonic crypts. The study demonstrates estrogen regulation of intestinal secretion both at a rapid and transcriptional level, demonstrating an interdependent relationship between both nongenomic and genomic hormone responses.

Functional Analysis of the ClC‐2 hyperpolarization‐activated Cl− channel in Mouse Colon.

ClC‐2 is a hyperpolarization‐activated Cl− channel expressed in epithelial cells lining the gastrointestinal tract. ClC‐2 expression has been proposed to compensate for the intestinal Cl− secretion deficit in cystic fibrosis due to mutations in the Cl− channel CFTR.The overall goal of this project was to evaluate the ability of the ClC‐2 Cl− channel to stimulate intestinal fluid secretion. Distal colon sheets from ClC‐2 +/+ and ClC‐2 −/− mice were mounted in Ussing chambers and Cl− secretion was induced by two different paradigms: a) cAMP‐ and b) Ca2+‐increasing secretagogues. Neither cAMP nor Ca2+ ‐ mediated Cl− secretion was affected in ClC‐2 −/− colon. In contrast, the amiloride‐inhibited short circuit current (ISC) increased in the early distal colon of ClC‐2 −/− mice.Based on our findings, the ClC‐2 channel appeared not to be necessary for Cl− secretion in colonic epithelium. On the other hand, increased amiloride‐sensitive ISC in the early distal colon of ClC‐2 −/− mice suggested that there was an increased expression of the epithelial Na+ channel ENaC, the key component of the electrogenic NaCl absorption process. We conclude that a compensatory NaCl absorptive mechanism was activated in the early distal colon of ClC‐2 −/− mice, implying that the ClC‐2 channel might be important for colonic NaCl absorption.This work was supported in part by grants from NIH (DE09626) and Takeda Pharmaceutical Company, Inc.

Cellular Mechanisms Underlying the Laxative Effect of Flavonol Naringenin on Rat Constipation Model

Background & AimsSymptoms of constipation are extremely common, especially in the elderly. The present study aim to identify an efficacious treatment strategy for constipation by evaluating the secretion-promoting and laxative effect of a herbal compound, naringenin, on intestinal epithelial anion secretion and a rat constipation model, respectively.Methods/Principal FindingsIn isolated rat colonic crypts, mucosal addition of naringenin (100 µM) elicited a concentration-dependent and sustained increase in the short-circuit current (ISC), which could be inhibited in Cl− free solution or by bumetanide and DPC (diphenylamine-2-carboxylic acid), but not by DIDS (4, 4′- diisothiocyanatostilbene-2, 2′-disulfonic acid). Naringenin could increase intracellular cAMP content and PKA activity, consisted with that MDL-12330A (N-(Cis-2-phenyl-cyclopentyl) azacyclotridecan-2-imine-hydrochloride) pretreatment reduced the naringenin-induced ISC. In addition, significant inhibition of the naringenin-induced ISC by quinidine indicated that basolateral K+ channels were involved in maintaining this cAMP-dependent Cl− secretion. Naringenin-evoked whole cell current which exhibited a linear I–V relationship and time-and voltage- independent characteristics was inhibited by DPC, indicating that the cAMP activated Cl− conductance most likely CFTR (cystic fibrosis transmembrane conductance regulator) was involved. In rat constipation model, administration of naringenin restored the level of fecal output, water content and mucus secretion compared to loperamide-administrated group.ConclusionsTaken together, our data suggest that naringenin could stimulate Cl− secretion in colonic epithelium via a signaling pathway involving cAMP and PKA, hence provide an osmotic force for subsequent colonic fluid secretion by which the laxative effect observed in the rat constipation model. Naringenin appears to be a novel alternative treatment strategy for constipation.

Membrane cholesterol content modulates activation of BK channels in colonic epithelia

Changes in the level of membrane cholesterol regulate a variety of signaling processes including those mediated by acylated signaling molecules that localize to lipid rafts. Recently several types of ion channels have been shown to have cholesterol-dependent activity and to localize to lipid rafts. In this study, we have investigated the role of cholesterol in the regulation of ion transport in colonic epithelial cells. We observed that methyl-β-cyclodextrin (MβCD), a cholesterol-sequestering molecule, activated transepithelial short circuit current ( I sc), but only from the basolateral side. Similar results were obtained with a cholesterol-binding agent, filipin, and with the sphingomyelin-degrading enzyme, sphingomyelinase. Experiments with ΔF508CFTR mutant mice indicated that raft disruption affected CFTR-mediated anion secretion, while pharmacological studies showed that this effect was due to activation of basolateral large conductance Ca 2+-activated K + (BK) channels. Sucrose density gradient centrifugation studies demonstrated that BK channels were normally present in the high-density fraction containing the detergent-insoluble cytoskeleton, and that following treatment with MβCD, BK channels redistributed into detergent-soluble fractions. Our evidence therefore implicates novel high-density cholesterol-enriched plasma membrane microdomains in the modulation of BK channel activation and anion secretion in colonic epithelia.

TGFβ down-regulation of the CFTR: a means to limit epithelial chloride secretion

Transforming growth factor β (TGFβ) is a multifunctional cytokine with effects on many cell types. We recently showed that in addition to epithelial barrier enhancing properties, TGFβ causes diminished cAMP-driven chloride secretion in colonic epithelia, in a manner that is p38 MAPK-dependent. In this study, we sought to further delineate the mechanism behind TGFβ diminution of chloride secretion. Using colonic and kidney epithelial cell lines, we found that exposure to TGFβ causes dramatic changes in the expression and localization of the apical membrane chloride channel, cystic fibrosis transmembrane conductance regulator (CFTR). In TGFβ-treated colonic epithelia (T84 and HT-29), CFTR mRNA was significantly reduced 2–24 h post-cytokine exposure. At a time consistent with decreased colonic epithelial secretory responses (16 h), TGFβ treatment caused diminished intracellular CFTR protein expression (confocal microscopy) and reduced channel expression in the apical membrane during stimulated chloride secretion (biotinylation assay). In comparison, polarized kidney epithelia (MDCK) treated with TGFβ displayed similarly reduced secretory responses to cAMP stimulating agents; however, a perinuclear accumulation of CFTR was observed, contrasting the diffuse cytoplasmic CFTR expression of control cells. Our data indicate that TGFβ has profound effects on the expression and subcellular localization of an important channel involved in cAMP-driven chloride secretion, and thus suggest TGFβ represents a key regulator of fluid movement.

TGF$beta; down-regulation of the CFTR: a means to limit epithelial chloride secretion

Transforming growth factor β (TGFβ) is a multifunctional cytokine with effects on many cell types. We recently showed that in addition to epithelial barrier enhancing properties, TGFβ causes diminished cAMP-driven chloride secretion in colonic epithelia, in a manner that is p38 MAPK-dependent. In this study, we sought to further delineate the mechanism behind TGFβ diminution of chloride secretion. Using colonic and kidney epithelial cell lines, we found that exposure to TGFβ causes dramatic changes in the expression and localization of the apical membrane chloride channel, cystic fibrosis transmembrane conductance regulator (CFTR). In TGFβ-treated colonic epithelia (T84 and HT-29), CFTR mRNA was significantly reduced 2–24 h post-cytokine exposure. At a time consistent with decreased colonic epithelial secretory responses (16 h), TGFβ treatment caused diminished intracellular CFTR protein expression (confocal microscopy) and reduced channel expression in the apical membrane during stimulated chloride secretion (biotinylation assay). In comparison, polarized kidney epithelia (MDCK) treated with TGFβ displayed similarly reduced secretory responses to cAMP stimulating agents; however, a perinuclear accumulation of CFTR was observed, contrasting the diffuse cytoplasmic CFTR expression of control cells. Our data indicate that TGFβ has profound effects on the expression and subcellular localization of an important channel involved in cAMP-driven chloride secretion, and thus suggest TGFβ represents a key regulator of fluid movement.

Regulation of Cl- secretion by alpha2-adrenergic receptors in mouse colonic epithelium

Previous studies have shown that α2 adrenoceptor (α2AR) agonists inhibit electrolyte secretion in colonic epithelia, but little is known about the molecular mechanisms involved in this process. In this study we examined the effect of α2AR activation on transepithelial anion secretion across isolated murine colonic epithelium. We found that α2AR agonists, UK 14,304, clonidine and medetomidine were potent inhibitors of anion secretion, especially in the proximal colon. Short circuit current measurements (Isc) in colonic epithelia from normal and cystic fibrosis (CF) mice showed that α2AR agonists inhibited basal cystic fibrosis transmembrane conductance regulator (CFTR)-mediated Cl− secretion but had no effect on CFTR activation by cAMP-dependent phosphorylation. Apical administration of an ionophore, nystatin (90 μg ml−1), was used to investigate the effect of UK 14,304 on basolateral K+ transport. The Na+–K+-ATPase current, measured as ouabain-sensitive current in the absence of ion gradients, was unaltered by pretreatment of the tissue with UK 14,304 (1 μm). In the presence of a basolaterally directed K+ gradient, UK 14,304 significantly reduced nystatin-activated Isc indicating that activation of α2ARs inhibits basolateral K+ channels. Studies with selective K+ channel inhibitors and openers showed that α2AR agonists inhibited KATP channels that were tonically active in mouse colonic epithelia. RT-PCR and pharmacological studies suggested that these channels could be similar to vascular smooth muscle KATP channels comprising Kir6.1/SUR2B or Kir6.2/SUR2B subunits. Inhibition of anion secretion by α2AR agonists required activation of pertussis toxin-sensitive Gi/o proteins, but did not involve classical second messengers, such as cAMP or Ca2+. In summary, α2ARs inhibit anion secretion in colonic epithelia by acting on basolateral KATP channels, through a process that does not involve classical second messengers.

Regulation of Cl- secretion by alpha2-adrenergic receptors in mouse colonic epithelium.

Previous studies have shown that alpha2 adrenoceptor (alpha2AR) agonists inhibit electrolyte secretion in colonic epithelia, but little is known about the molecular mechanisms involved in this process. In this study we examined the effect of alpha2AR activation on transepithelial anion secretion across isolated murine colonic epithelium. We found that alpha2AR agonists, UK 14,304, clonidine and medetomidine were potent inhibitors of anion secretion, especially in the proximal colon. Short circuit current measurements (Isc) in colonic epithelia from normal and cystic fibrosis (CF) mice showed that alpha2AR agonists inhibited basal cystic fibrosis transmembrane conductance regulator (CFTR)-mediated Cl- secretion but had no effect on CFTR activation by cAMP-dependent phosphorylation. Apical administration of an ionophore, nystatin (90 microg ml-1), was used to investigate the effect of UK 14,304 on basolateral K+ transport. The Na+-K+-ATPase current, measured as ouabain-sensitive current in the absence of ion gradients, was unaltered by pretreatment of the tissue with UK 14,304 (1 microM). In the presence of a basolaterally directed K+ gradient, UK 14,304 significantly reduced nystatin-activated Isc indicating that activation of alpha2ARs inhibits basolateral K+ channels. Studies with selective K+ channel inhibitors and openers showed that alpha2AR agonists inhibited KATP channels that were tonically active in mouse colonic epithelia. RT-PCR and pharmacological studies suggested that these channels could be similar to vascular smooth muscle KATP channels comprising Kir6.1/SUR2B or Kir6.2/SUR2B subunits. Inhibition of anion secretion by alpha2AR agonists required activation of pertussis toxin-sensitive Gi/o proteins, but did not involve classical second messengers, such as cAMP or Ca2+. In summary, alpha2ARs inhibit anion secretion in colonic epithelia by acting on basolateral KATP channels, through a process that does not involve classical second messengers.

17beta-oestradiol acutely regulates Cl- secretion in rat distal colonic epithelium.

In this study we used the short circuit current (ISC) technique to measure the non-genomic effects of the female sex steroid 17beta-oestradiol (E2) on electrogenic transepithelial ion transport in rat distal colonic epithelium. Basal ISC was largely composed of a transepithelial Cl- secretory component with minimal electrogenic Na+ movement. E2 (1-100 nM) caused a significant decrease in basal ISC after 15 min. In addition, pre-treating colonic epithelial tissues with E2 (0.1-100 nM) for 10 min significantly reduced forskolin (20 microM)-induced Cl- secretion. E2 also down-regulated Cl- secretion which was pre-stimulated by forskolin. Cl- secretory responses to the Ca2+-dependent secretagogue carbachol (10 microM) were also significantly reduced in the presence of E2 (10- 100 nM). However, E2 had no effect on amiloride-sensitive Na+ absorption. The rapid anti-secretory effect of E2 was abolished in the presence of the intracellular Ca2+ chelator BAPTA (50 microM) or the protein kinase C (PKC) inhibitor chelerythrine chloride (1 microM). However, in the presence of the nuclear oestrogen receptor antagonist tamoxifen (10 microM), E2 still produced an inhibition of Cl- secretion. Testosterone, progesterone and 17alpha-oestradiol had no significant effect on colonic Cl- secretion. Also, E2 (100 nM) did not alter Cl- secretion in colonic epithelia isolated from male rats. We conclude that E2 inhibits colonic Cl- secretion via a non-genomic pathway that involves intracellular Ca2+ and PKC. It is possible that this gender-specific mechanism contributes to the salt and water retention associated with high E2 states.

Forskolin- but not ionomycin-evoked Cl- secretion in colonic epithelia depends on intact microtubules

Several transport proteins are known to be trafficked to the cell membrane in response to appropriate secretagogues. In several cases, the response has been shown to be dependent on the cytoskeleton. We tested the hypothesis that the forskolin- and/or ionomycin-sensitive Cl- secretory response in colonic epithelia is dependent on an intact cytoskeleton. Using 125I- efflux as an assay for Cl- transport in the colonic epithelial cell line T84, we found that preincubation of the tissue for 3 h with either of two inhibitors of microtubule polymerization, nocodazole or colchicine, disrupted the cellular tubulin architecture and also reduced the forskolin- but not the ionomycin-evoked I- efflux. In contrast, brief exposure (4 min) to nocodazole was without effect on the forskolin-sensitive efflux, suggesting that the drug is not acting to block the stimulus-response pathway. An inactive structural analogue of colchicine, beta-lumicolchicine, had no inhibitory effect on either the forskolin-sensitive efflux or on microtubular structure. In a second model of Cl- secretion, the stripped rat colon, both colchicine and nocodazole reduced the forskolin-dependent short-circuit current by an average of 30-40%, suggesting a similar mechanism for insertion of Cl- channels into the plasma membrane. These findings suggest that the Cl- secretory response is dependent on microtubules and has a physiological role in the adenosine 3',5'-cyclic monophosphate-dependent, but not the Ca(2+)-dependent, Cl- secretion in colonic epithelia.