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Novel aspects of cholinergic regulation of colonic ion transport.

Bader S, Diener M - Pharmacol Res Perspect (2015)

Bottom Line: As a strong acetylcholinesterase activity was found in colonic epithelium, the effect of choline on I sc was examined.Although choline proved to be only a partial agonist, it concentration-dependently desensitized the response to acetylcholine, suggesting that it might act as a modulator of cholinergically induced anion secretion.Thus the cholinergic regulation of colonic ion transport - up to now solely explained by cholinergic submucosal neurons stimulating epithelial muscarinic receptors - is more complex than previously assumed.

View Article: PubMed Central - PubMed

Affiliation: Institute of Veterinary Physiology and Biochemistry, Justus-Liebig-University Giessen Giessen, Germany.

ABSTRACT
Nicotinic receptors are not only expressed by excitable tissues, but have been identified in various epithelia. One aim of this study was to investigate the expression of nicotinic receptors and their involvement in the regulation of ion transport across colonic epithelium. Ussing chamber experiments with putative nicotinic agonists and antagonists were performed at rat colon combined with reverse transcription polymerase chain reaction (RT-PCR) detection of nicotinic receptor subunits within the epithelium. Dimethylphenylpiperazinium (DMPP) and nicotine induced a tetrodotoxin-resistant anion secretion leading to an increase in short-circuit current (I sc) across colonic mucosa. The response was suppressed by the nicotinic receptor antagonist hexamethonium. RT-PCR experiments revealed the expression of α2, α4, α5, α6, α7, α10, and β4 nicotinic receptor subunits in colonic epithelium. Choline, the product of acetylcholine hydrolysis, is known for its affinity to several nicotinic receptor subtypes. As a strong acetylcholinesterase activity was found in colonic epithelium, the effect of choline on I sc was examined. Choline induced a concentration-dependent, tetrodotoxin-resistant chloride secretion which was, however, resistant against hexamethonium, but was inhibited by atropine. Experiments with inhibitors of muscarinic M1 and M3 receptors revealed that choline-evoked secretion was mainly due to a stimulation of epithelial M3 receptors. Although choline proved to be only a partial agonist, it concentration-dependently desensitized the response to acetylcholine, suggesting that it might act as a modulator of cholinergically induced anion secretion. Thus the cholinergic regulation of colonic ion transport - up to now solely explained by cholinergic submucosal neurons stimulating epithelial muscarinic receptors - is more complex than previously assumed.

No MeSH data available.


Related in: MedlinePlus

Effects of inhibitors of nicotinic acetylcholine receptor subunits on nicotine-evoked secretion. The Isc induced by nicotine (10−4 mol/L, applied in the presence of tetrodotoxin) across colonic mucosa preparations was tested either under control conditions (open bars) or in the presence of different inhibitors of nicotinic acetylcholine receptor subunits (solid bars). Inhibitors: dihydro-β-erythroidine (DhβE; 10−5 mol/L), α-bungarotoxin (10−6 mol/L), strychnine (10−5 mol/L), or (a high concentration of) atropine (2.5 × 10−5 mol/L). Values are given as increase in Isc (ΔIsc) above baseline just prior administration of nicotine and are means ± SEM; n = 5–6. *P < 0.05 vs. response evoked by nicotine in the respective control series.
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fig04: Effects of inhibitors of nicotinic acetylcholine receptor subunits on nicotine-evoked secretion. The Isc induced by nicotine (10−4 mol/L, applied in the presence of tetrodotoxin) across colonic mucosa preparations was tested either under control conditions (open bars) or in the presence of different inhibitors of nicotinic acetylcholine receptor subunits (solid bars). Inhibitors: dihydro-β-erythroidine (DhβE; 10−5 mol/L), α-bungarotoxin (10−6 mol/L), strychnine (10−5 mol/L), or (a high concentration of) atropine (2.5 × 10−5 mol/L). Values are given as increase in Isc (ΔIsc) above baseline just prior administration of nicotine and are means ± SEM; n = 5–6. *P < 0.05 vs. response evoked by nicotine in the respective control series.

Mentions: In order to further characterize the presumed epithelial nicotinic receptor subunits functionally, the interference of presumed subunit specific inhibitors with the secretory response induced by nicotinic receptor stimulation was tested. Inhibitors used were as follows: α-bungarotoxin, an inhibitor of α7, α8, and α9*-subunits, strychnine, which inhibits α7, α8, α9α10-subunits, dihydro-β-erythroidine, an inhibitor of, for example, α4β2 and α3β2 nicotinic receptors (for references to the inhibitors used, see Chavez-Noriega et al. 1997; Wonnacott and Barik 2007), and atropine, which (in concentrations higher than those needed for muscarinic receptor blockade) has been reported to inhibit, for example, α3β2, α3β4, α4β2, or α4β4 nicotinic receptors (Parker et al. 2003). The preincubation for 20 min with strychnine (10−5 mol/L) and atropine (2.5 × 10−5 mol/L) significantly inhibited the increase in Isc induced by nicotine (10−4 mol/L). In contrast, α-bungarotoxin (10−6 mol/L) or dihydro-β-erythroidine (10−5 mol/L) were ineffective (Fig.4). Even when the tissue was pretreated for 60 min with α-bungarotoxin (10−6 mol/L) to allow a better diffusion of this macromolecule to its presumed action sites, the nicotine-evoked increase in Isc was unaffected, as it amounted to 6.53 ± 1.39 μEq/h per cm2 (n = 6) in the absence and 7.27 ± 1.36 μEq/h per cm2 (n = 6) in the presence of this neurotoxin.


Novel aspects of cholinergic regulation of colonic ion transport.

Bader S, Diener M - Pharmacol Res Perspect (2015)

Effects of inhibitors of nicotinic acetylcholine receptor subunits on nicotine-evoked secretion. The Isc induced by nicotine (10−4 mol/L, applied in the presence of tetrodotoxin) across colonic mucosa preparations was tested either under control conditions (open bars) or in the presence of different inhibitors of nicotinic acetylcholine receptor subunits (solid bars). Inhibitors: dihydro-β-erythroidine (DhβE; 10−5 mol/L), α-bungarotoxin (10−6 mol/L), strychnine (10−5 mol/L), or (a high concentration of) atropine (2.5 × 10−5 mol/L). Values are given as increase in Isc (ΔIsc) above baseline just prior administration of nicotine and are means ± SEM; n = 5–6. *P < 0.05 vs. response evoked by nicotine in the respective control series.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4492755&req=5

fig04: Effects of inhibitors of nicotinic acetylcholine receptor subunits on nicotine-evoked secretion. The Isc induced by nicotine (10−4 mol/L, applied in the presence of tetrodotoxin) across colonic mucosa preparations was tested either under control conditions (open bars) or in the presence of different inhibitors of nicotinic acetylcholine receptor subunits (solid bars). Inhibitors: dihydro-β-erythroidine (DhβE; 10−5 mol/L), α-bungarotoxin (10−6 mol/L), strychnine (10−5 mol/L), or (a high concentration of) atropine (2.5 × 10−5 mol/L). Values are given as increase in Isc (ΔIsc) above baseline just prior administration of nicotine and are means ± SEM; n = 5–6. *P < 0.05 vs. response evoked by nicotine in the respective control series.
Mentions: In order to further characterize the presumed epithelial nicotinic receptor subunits functionally, the interference of presumed subunit specific inhibitors with the secretory response induced by nicotinic receptor stimulation was tested. Inhibitors used were as follows: α-bungarotoxin, an inhibitor of α7, α8, and α9*-subunits, strychnine, which inhibits α7, α8, α9α10-subunits, dihydro-β-erythroidine, an inhibitor of, for example, α4β2 and α3β2 nicotinic receptors (for references to the inhibitors used, see Chavez-Noriega et al. 1997; Wonnacott and Barik 2007), and atropine, which (in concentrations higher than those needed for muscarinic receptor blockade) has been reported to inhibit, for example, α3β2, α3β4, α4β2, or α4β4 nicotinic receptors (Parker et al. 2003). The preincubation for 20 min with strychnine (10−5 mol/L) and atropine (2.5 × 10−5 mol/L) significantly inhibited the increase in Isc induced by nicotine (10−4 mol/L). In contrast, α-bungarotoxin (10−6 mol/L) or dihydro-β-erythroidine (10−5 mol/L) were ineffective (Fig.4). Even when the tissue was pretreated for 60 min with α-bungarotoxin (10−6 mol/L) to allow a better diffusion of this macromolecule to its presumed action sites, the nicotine-evoked increase in Isc was unaffected, as it amounted to 6.53 ± 1.39 μEq/h per cm2 (n = 6) in the absence and 7.27 ± 1.36 μEq/h per cm2 (n = 6) in the presence of this neurotoxin.

Bottom Line: As a strong acetylcholinesterase activity was found in colonic epithelium, the effect of choline on I sc was examined.Although choline proved to be only a partial agonist, it concentration-dependently desensitized the response to acetylcholine, suggesting that it might act as a modulator of cholinergically induced anion secretion.Thus the cholinergic regulation of colonic ion transport - up to now solely explained by cholinergic submucosal neurons stimulating epithelial muscarinic receptors - is more complex than previously assumed.

View Article: PubMed Central - PubMed

Affiliation: Institute of Veterinary Physiology and Biochemistry, Justus-Liebig-University Giessen Giessen, Germany.

ABSTRACT
Nicotinic receptors are not only expressed by excitable tissues, but have been identified in various epithelia. One aim of this study was to investigate the expression of nicotinic receptors and their involvement in the regulation of ion transport across colonic epithelium. Ussing chamber experiments with putative nicotinic agonists and antagonists were performed at rat colon combined with reverse transcription polymerase chain reaction (RT-PCR) detection of nicotinic receptor subunits within the epithelium. Dimethylphenylpiperazinium (DMPP) and nicotine induced a tetrodotoxin-resistant anion secretion leading to an increase in short-circuit current (I sc) across colonic mucosa. The response was suppressed by the nicotinic receptor antagonist hexamethonium. RT-PCR experiments revealed the expression of α2, α4, α5, α6, α7, α10, and β4 nicotinic receptor subunits in colonic epithelium. Choline, the product of acetylcholine hydrolysis, is known for its affinity to several nicotinic receptor subtypes. As a strong acetylcholinesterase activity was found in colonic epithelium, the effect of choline on I sc was examined. Choline induced a concentration-dependent, tetrodotoxin-resistant chloride secretion which was, however, resistant against hexamethonium, but was inhibited by atropine. Experiments with inhibitors of muscarinic M1 and M3 receptors revealed that choline-evoked secretion was mainly due to a stimulation of epithelial M3 receptors. Although choline proved to be only a partial agonist, it concentration-dependently desensitized the response to acetylcholine, suggesting that it might act as a modulator of cholinergically induced anion secretion. Thus the cholinergic regulation of colonic ion transport - up to now solely explained by cholinergic submucosal neurons stimulating epithelial muscarinic receptors - is more complex than previously assumed.

No MeSH data available.


Related in: MedlinePlus