Electrogenic Secretion Research Articles

Allicin Induces Electrogenic Secretion of Chloride and Bicarbonate Ions in Rat Colon via the TRPA1 Receptor.

Allicin, an antioxidant from garlic, is known to regulate intestinal contractions, but its effect on intestinal ion transport is unclear. The aim of this study was to examine the role of allicin in the regulation of electrogenic ion transport in rat intestine by measuring the transmural potential difference (ΔPD). Allicin induced significant positive ΔPD, when administered to the serosal side of the colonic mucosal-submucosal preparation. Allicin-induced colonic ΔPD was largely diminished by incubation in the chloride-free solution, although the transient peak of ΔPD after application of allicin remained. This transient peak of ΔPD was significantly diminished in both the chloride- and the bicarbonate-free incubation solution. Induction of ΔPD by allicin was greatly diminished by AP-18, an inhibitor of the transient receptor potential (TRP) cation channel subfamily A member 1, TRPA1. Both alliin and S-allylcysteine, the analogues of allicin, had no effect on ΔPD and did not affect allicin-induced ΔPD in the colon. These results suggest that allicin mainly evokes the electrogenic chloride secretion and only partially increases the electrogenic bicarbonate secretion via TRPA1.

Origanum majorana L. extract exhibit positive cooperative effects on the main mechanisms involved in acute infectious diarrhea

Ethnopharmacological relevanceOriganum majorana L. (Lamiaceae) is commonly used in Moroccan folk medicine to treat infantile colic, abdominal discomfort and diarrhea. Liquid stools and abdominal discomfort observed in acute infectious diarrhea are the consequences of imbalance between intestinal water secretion and absorption in the lumen, and relaxation of smooth muscle surrounding the intestinal mucosa. Aim of the studyThe objective of our study was to see if aqueous extract of Origanum majorana L. (AEOM) may exhibit an effect on those deleterious mechanisms. Materials and methodsThe effect of AEOM on electrogenic Cl- secretion and Na+ absorption, the two main mechanisms underlying water movement in the intestine, was assessed on intestinal pieces of mice intestine mounted, in vitro, in Ussing chambers. AEOM effect on muscle relaxation was measured on rat intestinal smooth muscle mounted in an isotonic transducer. Results1) AEOM placed on the serosal (i.e. blood) side of the piece of jejunum entirely inhibited in a concentration-dependent manner the Forskolin-induced electrogenic chloride secretion, with an IC50 = 654 ± 8 µg/mL. 2) AEOM placed on the mucosal (i.e. luminal) side stimulated in a concentration-dependent manner an electrogenic Na+ absorption, with an IC50 = 476.9 ± 1 µg/mL. 3) AEOM (1 mg/mL) inhibition of Forskolin-induced electrogenic secretion was almost entirely prevented by prior exposure to Ca++ channels or neurotransmitters inhibitors. 4) AEOM (1 mg/mL) proabsorptive effect was greater in the ileum and progressively declined in the jejunum, distal colon and proximal colon (minimal). 5) AEOM inhibited in a concentration-dependent manner smooth muscle Carbachol or KCl induced contraction, with an IC50 = 1.64 ± 0.2 mg/mL or 1.92 ± 0.8 mg/mL, respectively. Conclusionthe present results indicate that aqueous extract of Origanum majorana L. exhibit positive cooperative effects on the main mechanisms that are involved in acute infectious diarrhea.

The Effect of Deoxycholic Acid on Secretion and Motility in the Rat and Guinea Pig Large Intestine.

Background/AimsBile acid is an important luminal factor that affects gastrointestinal motility and secretion. We investigated the effect of bile acid on secretion in the proximal and distal rat colon and coordination of bowel movements in the guinea pig colon.MethodsThe short-circuit current from the mucosal strip of the proximal and distal rat colon was compared under control conditions after induction of secretion with deoxycholic acid (DCA) as well as after inhibition of secretion with indomethacin, 1,2-bis (o-aminophenoxy) ethane-N,N,N′,N′-tetra-acetic acid (an intracellular calcium chelator; BAPTA), and tetrodotoxin (TTX) using an Ussing chamber. Colonic pressure patterns were also evaluated in the extracted guinea pig colon during resting, DCA stimulation, and inhibition by TTX using a newly developed pressure-sensing artificial stool.ResultsThe secretory response in the distal colon was proportionate to the concentration of DCA. Also, indomethacin, BAPTA, and TTX inhibited chloride secretion in response to DCA significantly (P < 0.05). However, these changes were not detected in the proximal colon. When we evaluated motility, we found that DCA induced an increase in luminal pressure at the proximal, middle, and distal sensors of an artificial stool simultaneously during the non-peristaltic period (P < 0.05). In contrast, during peristalsis, DCA induced an increase in luminal pressure at the proximal sensor and a decrease in pressure at the middle and distal sensors of the artificial stool (P < 0.05).ConclusionsDCA induced a clear segmental difference in electrogenic secretion. Also, DCA induced a more powerful peristaltic contraction only during the peristaltic period.

Severe changes in colon epithelium in the Mecp2-null mouse model of Rett syndrome.

BackgroundRett syndrome is best known due to its severe and devastating symptoms in the central nervous system. It is produced by mutations affecting the Mecp2 gene that codes for a transcription factor. Nevertheless, evidence for MECP2 activity has been reported for tissues other than those of the central nervous system. Patients affected by Rett presented with intestinal affections whose origin is still not known. We have observed that the Mecp2-null mice presented with episodes of diarrhea, and decided to study the intestinal phenotype in these mice.Methods Mecp2-null mice or bearing the conditional intestinal deletion of MECP2 were used. Morphometirc and histologic analysis of intestine, and RT-PCR, western blot and immunodetection were perfomed on intestinal samples of the animals. Electrical parameters of the intestine were determined by Ussing chamber experiments in freshly isolated colon samples.ResultsFirst we determined that MECP2 protein is mainly expressed in cells of the lower part of the colonic crypts and not in the small intestine. The colon of the Mecp2-null mice was shorter than that of the wild-type. Histological analysis showed that epithelial cells of the surface have abnormal localization of key membrane proteins like ClC-2 and NHE-3 that participate in the electroneutral NaCl absorption; nevertheless, electrogenic secretion and absorption remain unaltered. We also detected an increase in a proliferation marker in the crypts of the colon samples of the Mecp2-null mice, but the specific silencing of Mecp2 from intestinal epithelium was not able to recapitulate the intestinal phenotype of the Mecp2-null mice.ConclusionsIn summary, we showed that the colon is severely affected by Mecp2 silencing in mice. Changes in colon length and epithelial histology are similar to those observed in colitis. Changes in the localization of proteins that participate in fluid absorption can explain watery stools, but the exclusive deletion of Mecp2 from the intestine did not reproduce colon changes observed in the Mecp2-null mice, indicating the participation of other cells in this phenotype and the complex interaction between different cell types in this disease.Electronic supplementary materialThe online version of this article (doi:10.1186/s40348-016-0065-3) contains supplementary material, which is available to authorized users.

Characterization of the Electrogenic Secretory Response in the Porcine Colon following in vivo Challenge with Brachyspira hyodysenteriae and “Brachyspira hampsonii”

The effects of Brachyspira hyodysenteriae and “Brachyspira hampsonii” infections on the agonist induced electrogenic secretion were assessed to determine their contribution to the pathophysiology of swine dysentery. Proximal, apex and distal sections of colon were compared in healthy and diseased purebred Yorkshire grower pigs in Ussing chambers. Activation of secretion via isoproterenol (adrenergic agonist), carbachol (cholinergic agonist) and forskolin / 3‐isobutyl‐1‐methylxanthine (IBMX) demonstrated a significantly decreased change in short‐circuit current (Isc) in infected pigs in all three sections of colon compared to control, confirming the previous observation that swine dysentery is not secretory in nature. Tissue resistances did not account for this difference, rather, it was attributed to a decrease in Cl− secretion as indicated by a significant decrease in bumentanide inhibitable short‐circuit current in infected animals. qRT‐PCR was conducted to determine if a decrease in gene transcript was responsible for the loss of Cl− secretory function. The major chloride transport proteins of the epithelium, such as the Cystic Fibrosis transmembrane conductance regulator (CFTR), Transmembrane member protein 16A (TMEM16A) and Na‐K‐Cl co‐transporter 1 (NKCC1) were compared between healthy and diseased animals in all three sections of colon. Inflammatory mediators were also assed to probe potential mechanism behind the transporter modulation. mRNA expression for these channels were determined to be elevated in the infected samples compared to controls. This suggests that these Brachyspira species reduce the Cl− secretory response by directly inhibiting Cl− channels or by inhibiting the translation of mRNA into protein.Support or Funding InformationNatural Sciences and Engineering Research Council (NSERC) 371364 / 2010 to MEL &amp; Alberta Livestock and Meat Association (ALMA) 2013R054R to JCH, MEL &amp; JEH

Tu1389 Increased Basolateral Small Conductance Potassium Channel (KCNQ1/ KCNE3) Activity in Ulcerative Colitis

Introduction and Aims: Basolateral K+ channels keep colonic cells in a hyperpolarized state to ensure transcellular ionic movements. Intermediate conductance K+ (IK) channels dominate the basolateral membrane conductance in human colonic cells, but their expression and activity are markedly decreased in ulcerative colitis (UC), thus contributing to defective Na+ and water absorption across inflamed mucosa (J Pathol 2012;226:463-470). This study is the first to characterize basolateral small conductance (KCNQ1/KCNE3) K+ channels in normal human colon, and explore their activity in UC. Methods: Intact crypts were isolated from distal colonic biopsies taken while investigating patients with functional diarrhea (normals) and patients with UC not receiving steroids. Expression of KCNQ1 and KCNE3 mRNAs was determined by qPCR. Patch clamp recording was used to study (i) basolateral KCNQ1/KCNE3 channel activity in normal and UC crypt cells and (ii) in normal crypts cells, the effects of forskolin (an activator of adenylate cyclase) and inflammatory mediators present at high concentrations in UC. Results: qPCR product bands were of the expected size (KCNQ1 160 bp, KCNE3 119 bp, β-actin 148 bp). Product identity was confirmed by automated sequencing and melting curve analysis, and KCNQ1 and KCNE3 mRNA expression was similar in normal and UC patients. In normal crypts (n=34), usually single channels (conductance 6.8 ± 0.5 pS) were seen in 36% of patches, whereas in UC crypts (n=9), two or more channels were seen in 74% of patches, the difference in channel prevalence between the two groups being significant (P<0.001). Overall channel activity was 10-fold greater in UC than control patients (P<0.001). These channels constituted a greater calculated basolateral conductance (GSK) in UC (5.85 ± 0.62 mS.cm-2) than in control patients (0.28 ± 0.04 mS.cm-2, P<0.001), but this increase in GSK did not compensate for the decrease in basolateral membrane conductance (from 22 mS.cm-2 to 5 mS.cm-2) previously attributed to decreased IK channel expression/activity in UC (J Pathol 2012;226:463-470). In control crypts, 10μM forskolin and 1μM thromboxane A2 stimulated channel activity 30-fold (n=8, P<0.005) and 10-fold (n=5, P<0.05) respectively, while 100nM PGE2, 10nM IL-1β and 1μM LTD4 had no effect. Conclusions: Crypt cells in normal human colon express cAMP-activated KCNQ1/ KCNE3 channels which make a far smaller contribution to overall basolateral conductance than IK channels. In active UC, KCNQ1/KCNE3 channel activity is significantly increased, but this fails to compensate for the depolarizing effect of decreased IK channel expression/ activity. This may explain, at least in part, why defective electrogenic Na+ absorption rather than increased electrogenic Cl secretion is the dominant pathophysiological mechanism of diarrhea in active UC (J Pathol 2012;226:463-470).

VPAC1 receptors regulate intestinal secretion and muscle contractility by activating cholinergic neurons in guinea pig jejunum

In the gastrointestinal tract, vasoactive intestinal peptide (VIP) is found exclusively within neurons. VIP regulates intestinal motility via neurally mediated and direct actions on smooth muscle and secretion by a direct mucosal action, and via actions on submucosal neurons. VIP acts via VPAC1 and VPAC2 receptors; however, the subtype involved in its neural actions is unclear. The neural roles of VIP and VPAC1 receptors (VPAC1R) were investigated in intestinal motility and secretion in guinea pig jejunum. Expression of VIP receptors across the jejunal layers was examined using RT-PCR. Submucosal and myenteric neurons expressing VIP receptor subtype VPAC1 and/or various neurochemical markers were identified immunohistochemically. Isotonic muscle contraction was measured in longitudinal muscle-myenteric plexus preparations. Electrogenic secretion across mucosa-submucosa preparations was measured in Ussing chambers by monitoring short-circuit current. Calretinin(+) excitatory longitudinal muscle motor neurons expressed VPAC1R. Most cholinergic submucosal neurons, notably NPY(+) secretomotor neurons, expressed VPAC1R. VIP (100 nM) induced longitudinal muscle contraction that was inhibited by TTX (1 μM), PG97-269 (VPAC1 antagonist; 1 μM), and hyoscine (10 μM), but not by hexamethonium (200 μM). VIP (50 nM)-evoked secretion was depressed by hyoscine or PG97-269 and involved a small TTX-sensitive component. PG97-269 and TTX combined did not further depress the VIP response observed in the presence of PG97-269 alone. We conclude that VIP stimulates ACh-mediated longitudinal muscle contraction via VPAC1R on cholinergic motor neurons. VIP induces Cl(-) secretion directly via epithelial VPAC1R and indirectly via VPAC1R on cholinergic secretomotor neurons. No evidence was obtained for involvement of other neural VIP receptors.

Neural involvement in 5-hydroxytryptamine-induced net electrogenic ion secretion in the rat intestine in-vivo.

5-Hydroxytryptamine (5-HT) induces active electrogenic anion secretion by both the small intestine and the colon, responses that can be detected from measurements of transmural electrical activity. This approach was adopted to examine the involvement of neural mechanisms in 5-HT-induced secretion in rat proximal jejunum, distal ileum and proximal colon in-vivo. Under control conditions, 5-HT caused maximum rises in transintestinal potential difference of 4.7 +/- 0.3, 3.8 +/- 0.4 and 7.6 +/- 0.3 mV, respectively, with corresponding ED50 values of 28 +/- 3, 38 +/- 4 and 41 +/- 4 nmol kg-1 (n = 12). In each region examined a neural component in the secretory response to 5-HT was identified. Hexamethonium (22 mumol kg-1) reduced the 5-HT response in each region: in the jejunum and colon, it also attenuated the responses to the 5-HT3 agonist, phenylbiguanide and to 5-methoxytryptamine (5-MeOT), an agonist at all 5-HT receptors except 5-HT3, indicating that in these regions the nicotinic pathway can be activated by more than one 5-HT receptor subtype. Atropine (0.27 and 2.7 mumol kg-1) was found to have regional effects on the intestinal responses to 5-HT receptor agonists. In the jejunum, evidence for a pro-secretory muscarinic pathway which could be activated by more than one 5-HT receptor subtype was found. In the ileum and colon no muscarinic pro-secretory pathway was identified, indeed in the colon, an anti-secretory pathway may be present. This muscarinic anti-secretory pathway was observed with phenylbiguanide and 5-MeOT, but not 5-HT. Substance P release does not appear to be involved in mediating the intestinal secretory response to 5-HT. 5-HT-induced intestinal anion secretion may involve a direct secretory action on the enterocyte which can be modified by neurally-mediated pro-secretory and anti-secretory pathways, the balance between these processes varying down the length of the gut.

Do 5-HT4 receptors mediate the intestinal secretory response to 5-HT in rat in-vivo?

The involvement of the recently characterized 5-HT4 receptor in the actions of 5-hydroxytryptamine (5-HT) on jejunal, ileal and colonic electrogenic ion secretion was investigated in the rat in-vivo. 5-HT and the 5-HT1-, 5-HT2- and 5-HT4-receptor agonist 5-methoxytryptamine (5-MeOT), induced a rise in transintestinal PD in all regions of the gut. However, the 5-HT4-receptor agonists renzapride and cisapride had no effect. Furthermore, the 5-HT4-receptor antagonists SDZ 205-557 (2-diethylaminoethyl-[2-methoxy-4-amino-5-chloro] benzoate), tropisetron and SB 204070 ([1-butyl-4-piperidinylmethyl]-8-amino-7-chloro-1,4- benzodioxan-5-carboxylate hydrochloride) did not affect the secretory response to either 5-HT or 5-MeOT in the jejunum, but did cause a small inhibition in the ileum and colon. It is concluded that 5-HT4 receptors do not make a contribution to the electrically monitored 5-HT intestinal secretory response in the rat jejunum in-vivo, but may play a small role in the ileum and colon.

Cholinergic modulation of electrogenic ion transport in different regions of the rat small intestine.

Acetylcholine acting via muscarinic receptors located in the intestinal mucosa controls ion and fluid transport. This study examined the pathway(s) by which cholinergic receptors mediate secretion in rat isolated duodenum, jejunum and ileum using the short-circuit current (Isc) as an index of electrogenic CL- secretion. Carbachol and bethanechol induced electrogenic CL- transport which was insensitive to the neural blocker tetrodotoxin, indicating their direct action on the enterocytes. Functional characterization of electrogenic secretion activated via muscarinic receptors on jejunal and ileal enterocytes was achieved by use of selective muscarinic antagonists in the presence of tetrodotoxin. In both regions the rank order of potency of these compounds (atropine > 4-diphenylacetoxy-N-piperidine methiodide (4-DAMP) > hexahydro-sila-difenidol (HHSiD) > pirenzepine > methoctramine) indicated the M3 receptor subtype. Secretion activated by the muscarinic agonist 4-[[(3-chlorophenyl)amino]carbonyl]-N,N, N-trimethyl-2-butyn-1-ammonium chloride (McN-A-343) was sensitive to tetrodotoxin and pirenzepine but not to the ganglionic blocker, hexamethonium, indicating the M1 receptor subtype on post ganglionic neurons. Regional differences for bethanechol-activated secretion showed an increasing gradient in secretory capacity (Isc max) in a proximal-to-distal direction along the small intestine. Responses to McN-A-343 also showed regional differences but these were unlike those of bethanechol. These results show that cholinomimetic-induced electrogenic CL- secretion in rat isolated small intestine appears to be mediated by two dissimilar populations of muscarinic receptor: M3 muscarinic receptors positioned on enterocytes and M1 muscarinic receptors sited on submucosal neurons.

Strain‐dependent differences in electrogenic secretion of electrolytes across mouse colon epithelium

Mice have proven to be powerful models for the study of human physiology and pathophysiology. With the advent of techniques for genomic manipulation, the possibilities for studying inherited diseases in this convenient laboratory mammal are increasing by the day. It has been reported that when knocking out or otherwise modifying genes of interest in mice, the phenotype obtained can vary markedly depending on the genetic background of the animals used in the study. The aim of this work was to study whether the genetic background can influence the characteristics of fluid and electrolyte transepithelial transport in the distal colon of three mouse strains most in use in our and other laboratories. Ussing chamber recordings revealed that the colons of C57Bl/6J, Sv 129 and Black Swiss animals have distinctive responses to the calcium agonists carbachol and histamine that are not explained by the presence of different types of muscarinic and histaminergic receptors in these tissues. We have also found differences in the cAMP-activated, KCNMA1-channel-dependent potassium secretion between the strains. We interpret this to indicate a unique distribution of KCNMA1 channels in lower parts of the crypt of Sv 129 colonic epithelium compared with that of C57Bl/6J and Black Swiss animals. The reported differences should be taken into account when choosing the genetic background of animals to be used for genetic modification.

Getting a Handle on Cholera and the Circuits Controlling Intestinal Motility

Getting a Handle on Cholera and the Circuits Controlling Intestinal Motility

Differences in electrogenic secretion of electrolytes in colonic epithelium of inbred mouse strains.

The mouse is the animal model of choice in studies of the physiology and pathophysiology of intestinal fluid and electrolyte transport. In the course of our research in colon physiology we have observed differences in electrical tissue properties and responses to agonists that induce electrogenic secretion of electrolytes among mice strains. Such differences are important enough to preclude comparisons between strains and might be crucial when choosing the genetic background for knockout of genes of interest. We have now investigated some of these differences by electrophysiological methods. Colonic tissue from Black Swiss, 129Sv and B6 mice were placed in Ussing chambers and their responses to a series of agonists and blockers recorded. We observe that while the 3 strains have similar anion secretory responses to increasing cAMP (around ‐100 μA cm−2), when the muscarinic agonist carbachol was used the largest response was seen with B6 tissue, compared to that of Black Swiss and 129Sv colon (‐200, ‐163 and ‐133 μA cm−2 respectively). The importance of the genetic background on the severity of cystic fibrosis in mice has long been known (Rozmahel et al., Nat Genet 12: 280‐7, 1996) and has been related to differences in calcium‐dependent anion secretion. We reported previously that basolateral KCNN4 calcium‐activated potassium channels are the rate‐limiting step in calcium‐agonist‐dependent anion secretion, rather than apical CFTR chloride channels (Flores et al., J Physiol 583: 705‐17, 2007). We are studying KCNN4 expression as a possible explanation to these differences.Supported by FONDECYT 3085023

5-Hydroxytryptamine Induces Electrogenic Secretion in the Duodenum of Gerbil (Gerbillus cheesmani)

The effect of serosally added 5-hydroxytryptamine (5-HT 100 I¼M) on the short circuitcurrent (Isc) across duodenum taken from fed, starved (4 days, water ad lib) and undernourished (50% control food intake for 21 days) gerbils (Gerbillus cheesmani) were investigated. The effect of the neurotoxin, tetrodotoxin (TTX 10 I¼M) and atropine (100I¼M) on the maximum increase in Isc induced by 5-HT were also studied. The 5-HT-induced Isc were higher in unstripped than in the stripped sheets in the three feeding conditions. TTX reduced the maximum increase in Isc induced by 5-HT across stripped and unstripped sheets taken from fed, starved and undernourished gerbils. Atropine decreased the 5-HT-induced Isc of stripped sheets in the three feeding conditions and it also decreased the 5-HTinduced Isc in unstripped sheets in fed duodenum. Therefore, the duodenal response to 5-HT occur partly by activation of a nonneural pathway and partly by activating electrogenic ion transport via muscarinic neural mechanism. It also showed that the 5-HT-induced Isc was chloride-dependent in fed duodenum and were chloride and bicarbonate dependent in the duodenum taken from starved and undernourished gerbil The results also showed that the increase in 5-HT-induced Isc as a results of starvation and undernourishment were TTX-sensitive and both chloride and bicarbonate dependent.

Clostridium perfringens alpha toxin affects electrophysiological properties of isolated jejunal mucosa of laying hens

Bacteria that colonize the intestinal tract can invade epithelial cells or produce toxins that cause diarrhoeal diseases. Proliferation of Clostridium perfringens and production of alpha-toxin, a phospholipase C, is the major factor for necrotic enteritis in poultry. However, little is known about the functional importance of luminal alpha-toxin during intestinal infection. The purpose of this study was to investigate the effects of purified alpha toxin of Clostridium perfringens on the electrophysiology of the laying hen's stripped jejunum in Ussing chambers. The effects were investigated in Experiment 1 after toxin addition to the mucosal and serosal side of the tissue, and a second experiment was performed to study the effect of the toxin on sodium-dependent glucose transport. Mucosal exposure of jejunal tissue sheets to 100 units of alpha toxin/L did not elicit electrophysiologic changes. The addition of purified alpha toxin to the serosal side induced a biphasic increase in short-circuit current (ISC) after 15 and 100 min. The magnitude of the increase of ISC of both peaks was similar, but the second phase response lasted longer. The tissue conductivity tended (P = 0.07) to be lower after 2 h of toxin addition compared with basal value when no toxin was added. In the second experiment, adding D-glucose on the mucosal side of the jejunum increased (P < 0.05) the ISC from a baseline value of 42 ± 28 µA/cm2 to a maximal value of 103 ± 27 µA/cm2. Preincubation with α-toxin almost fully inhibited this stimulation of ISC by D-glucose. The conductance of the tissues was not affected by the toxin addition. These findings indicate that alpha toxin not only causes electrogenic secretion of anions, probably due to the stimulation of chloride secretion, but also diminishes electrogenic Na+/glucose cotransport from the mucosal to serosal side in the small intestine of poultry.

Segmental heterogeneity of electrogenic secretions in human ascending colon and rectum

We have attempted to ascertain putative segmental differences in the secretory responses of the human ascending colon and rectum. From the mucosal biopsy samples of two segments, the short-circuit current (I(sc)) and tissue resistance (R(te)) were compared under control conditions, as well as after the induction of secretion, using a modified Ussing chamber. We also performed semiquantitative reverse transcriptase-polymerase chain reaction (RT-PCR) to detect and quantify transport proteins. The spontaneous I(sc) in the ascending colon was found to be greater than that in the rectum (P<0.01), whereas isobutylmethylxanthine/forskolin and carbachol (CCh) induced a greater rise in I(sc) in the rectum than in the ascending colon (P<0.05). When coupled with indomethacin pretreatment, the increase in Delta I(sc) after the addition of CCh and forskolin was significant as compared to that observed without pretreatment (P<0.05). However, in the rectum, the secretory response to CCh and forskolin was abolished to a significant degree by indomethacin (P<0.05). Moreover, these indomethacin-induced changes were reversed by the addition of PGE2. Upon semiquantitative RT-PCR analysis, the amounts of cystic fibrosis transmembrane regulator, KCNQ1, and CLCA1 mRNAs were not found to be different between the two segments. There was a clear segmental heterogeneity with regard to electrogenic secretion in the human colon, and this difference can be explained by differences in the ascending colon and rectum.

Endolymphatic sodium homeostasis by REISSNER’s membrane

Cochlear sensory transduction depends on active extrusion of sodium ion (Na +) from the luminal fluid, endolymph. Reissner’s membrane epithelium forms much of the barrier between cochlear endolymph and perilymph and we hypothesized that Reissner’s membrane might be responsible for this function. We found that Reissner’s membrane isolated from gerbil produced a short circuit current ( I sc) directed into the apical side, consistent with cation absorption and/or anion secretion. I sc was inhibited by amiloride analogs in the potency sequence benzamil>amiloride>>ethylisopropylamiloride, consistent with Na + absorption through an epithelial sodium channel in the apical cell membrane. I sc was also inhibited by an inhibitor of Na +,K +-ATPase, ouabain, and by the K + channel blockers Ba 2+, 4-aminopyridine and quinine but not tetraethylammonium nor glibenclamide, consistent with the presence of a voltage-activated K + channel. Bumetanide, an inhibitor of the Na +,2Cl −,K +-cotransporter, had no effect on I sc. Contrary to previous hypotheses, no evidence was found for electrogenic secretion of Cl − under control of cAMP since neither forskolin nor genistein affected I sc when Na + absorption was blocked. These results provide the first direct evidence that Reissner’s membrane contributes to normal cochlear function by absorption of Na + from endolymph.

Secretory modulation of basolateral membrane inwardly rectified K(+) channel in guinea pig distal colonic crypts.

Cell-attached recordings revealed K(+) channel activity in basolateral membranes of guinea pig distal colonic crypts. Inwardly rectified currents were apparent with a pipette solution containing 140 mM K(+). Single-channel conductance (gamma) was 9 pS at the resting membrane potential. Another inward rectifier with gamma of 19 pS was observed occasionally. At a holding potential of -80 mV, gamma was 21 and 41 pS, respectively. Identity as K(+) channels was confirmed after patch excision by changing the bath ion composition. From reversal potentials, relative permeability of Na(+) over K(+) (P(Na)/P(K)) was 0.02 +/- 0.02, with P(Rb)/P(K) = 1.1 and P(Cl)/P(K) < 0.03. Spontaneous open probability (P(o)) of the 9-pS inward rectifier ((gp)K(ir)) was voltage independent in cell-attached patches. Both a low (P(o) = 0.09 +/- 0.01) and a moderate (P(o) = 0.41 +/- 0.01) activity mode were observed. Excision moved (gp)K(ir) to the medium activity mode; P(o) of (gp)K(ir) was independent of bath Ca(2+) activity and bath acidification. Addition of Cl(-) and K(+) secretagogues altered P(o) of (gp)K(ir). Forskolin or carbachol (10 microM) activated the small-conductance (gp)K(ir) in quiescent patches and increased P(o) in low-activity patches. K(+) secretagogues, either epinephrine (5 microM) or prostaglandin E(2) (100 nM), decreased P(o) of (gp)K(ir) in active patches. This (gp)K(ir) may be involved in electrogenic secretion of Cl(minus sign) and K(+) across the colonic epithelium, which requires a large basolateral membrane K(+) conductance during maximal Cl(-) secretion and, presumably, a lower K(+) conductance during primary electrogenic K(+) secretion.

Coordination between intestinal motility and electrogenic mucosal secretion — A comparison between males and females

Coordination between intestinal motility and electrogenic mucosal secretion — A comparison between males and females

Coordination between intestinal motility and electrogenic mucosal secretion — A comparison between males and females

Coordination between intestinal motility and electrogenic mucosal secretion — A comparison between males and females