Alkaline Secretion Research Articles

The method of alkaline loading and its application in the clinic of internal diseases

The works of recent years have clearly shown the importance that the alkaline-acid balance has in the physiology and pathology of the animal organism. The desire to maintain this balance at a certain height occurs by coordinating the work of a number of organs: the lungs, secreting C02, the liver, taking part in the production of ammonia, the gastrointestinal tract, secerning acid and alkaline secretions and, finally, the kidneys, giving urine with a high acid content and someone's slit, then with less-take part in the regulation of alkalineacid balance. That is why, naturally, the study of the functions of various organs aimed at regulating and maintaining the alkaline-acid balance attracted the attention of clinicians. Rehn and Gnzburg, then Pannewitz, Popescu, Inotesti. Su11a, and finally Rosenberg and Hellfors, studying fluctuations in the concentration of hydrogen ions in urine after loading with alkalis and acids, sought to gain an idea of kidney function aimed at maintaining the gap.- acids. balance, and at the same time apply this method to the study of the functional state of the kidneys in general. However, it turned out to be insufficient to talk about this condition on the basis of determining the Ph of urine. The Ph fluctuations are not always sufficiently prominent, as the review of the data obtained by the authors shows, because the concentration of hydrogen ions is a value depending on the ratio of acid to alkali (voltage 002 and bicarbonate content). This forced us to put forward another method for determining changes in the functions of tissues and kidneys for the introduction of alkali: Mainzer et al., A. G e f t e r emphasized the importance of the determination of bicarbonates in urine and suggested using the method of their determination by gasometric method (according to van Slyke'y), while giving this definition a much greater value than the study of Ph fluctuations alone.

To the pharmacology of the uterine glands

From the physiology of the female genital area, it is known that the alkaline secretion, secreted by the uterine glands, plays a very important role in the woman's body, creating favorable conditions for pregnancy.

Study of oral microorganisms contributing to non-carious cervical lesions via bacterial interaction and pH regulation.

There is a lack of evidence about the relationship between microorganisms and non‐carious cervical lesions (NCCLs) due to limited technologies. A group of 78 patients was enrolled for microbial 16S rRNA sequencing of dental plaques on normal and defective cervical surfaces. Parallel data from 39 patients were analysed with paired t tests, and Fusobacteriales exhibited significantly less distribution on NCCLs than on normal surfaces. As a result, Fusobacterium nucleatum, the most common oral bacterial strain belonging to the order Fusobacteriales, was selected for further research. From a scanning electron microscopy (SEM) scan, the tooth surface with Fusobacterium nucleatum and Streptococcus mutans culture was more intact than that without Fusobacterium nucleatum. Furthermore, the calcium contents in groups with Fusobacterium nucleatum were significantly higher than that without it. In further mechanistic research, Fusobacterium nucleatum was demonstrated to adhere to and disturb other organisms as well as producing alkaline secretions to neutralize the deleterious acidic environment, protecting the tooth structure. In conclusion, microorganisms and NCCLs were confirmed directly related through adherent bacterial interactions and pH regulation. The research provides a new perspective and experimental evidence for the relation between microorganisms and NCCLs, which guides clinical treatment and preventive dentistry in the future.

Histochemical localisation of carbonic anhydrase in the digestive tract and salivary glands of the house cricket, Acheta domesticus

The house cricket (Acheta domesticus) is one of several cricket species with great potential to be farmed as a sustainable protein source. In order to succeed in large-scale cricket farming, knowledge of cricket digestion is essential. The digestive tract morphology of A. domesticus is well documented, but knowledge of the salivary glands is lacking. In the digestive tract of insects, the carbonic anhydrase (CA) enzyme family is believed to contribute to the luminal pH gradient. Presence of CA in the digestive tract of A. domesticus has been reported, but not the cellular localisation. This study examined the digestive tract of A. domesticus, including salivary glands, and the cellular localisation and activity of CA in fed or starved (48 h) males and females. Tissues were collected from third-generation offspring of wild A. domesticus captured in Sweden and the histology of the salivary glands and the cellular localisation of CA in the digestive tract of A. domesticus were determined, to our knowledge for the first time. The salivary glands resembled those of grasshoppers and locusts, and we suggest the two main cell types present to be parietal and zymogenic cells. Histochemical analysis revealed that CA activity was localised in midgut epithelium, both main cell types of salivary gland, and muscle along the entire digestive tract. These findings support the suggestion that CA contributes to digestive tract luminal pH gradient, by driving acidic secretions from the salivary glands and alkaline secretions from the midgut. Starvation resulted in significantly reduced body size and weight, but neither starvation nor sex had any effect on CA activity or localisation.

Perturbation Analysis of Calcium, Alkalinity and Secretion during Growth of Lily Pollen Tubes.

Pollen tubes grow by spatially and temporally regulated expansion of new material secreted into the cell wall at the tip of the tube. A complex web of interactions among cellular components, ions and small molecule provides dynamic control of localized expansion and secretion. Cross-correlation studies on oscillating lily (Lilium formosanum Wallace) pollen tubes showed that an increase in intracellular calcium follows an increase in growth, whereas the increase in the alkaline band and in secretion both anticipate the increase in growth rate. Calcium, as a follower, is unlikely to be a stimulator of growth, whereas the alkaline band, as a leader, may be an activator. To gain further insight herein we reversibly inhibited growth with potassium cyanide (KCN) and followed the re-establishment of calcium, pH and secretion patterns as growth resumed. While KCN markedly slows growth and causes the associated gradients of calcium and pH to sharply decline, its removal allows growth and vital processes to fully recover. The calcium gradient reappears before growth restarts; however, it is preceded by both the alkaline band and secretion, in which the alkaline band is slightly advanced over secretion. Thus the pH gradient, rather than the tip-focused calcium gradient, may regulate pollen tube growth.

Proton Pump Inhibitors Inhibit Pancreatic Secretion: Role of Gastric and Non-Gastric H+/K+-ATPases.

The mechanism by which pancreas secretes high HCO3 - has not been fully resolved. This alkaline secretion, formed in pancreatic ducts, can be achieved by transporting HCO3 - from serosa to mucosa or by moving H+ in the opposite direction. The aim of the present study was to determine whether H+/K+-ATPases are expressed and functional in human pancreatic ducts and whether proton pump inhibitors (PPIs) have effect on those. Here we show that the gastric HKα1 and HKβ subunits (ATP4A; ATP4B) and non-gastric HKα2 subunits (ATP12A) of H+/K+-ATPases are expressed in human pancreatic cells. Pumps have similar localizations in duct cell monolayers (Capan-1) and human pancreas, and notably the gastric pumps are localized on the luminal membranes. In Capan-1 cells, PPIs inhibited recovery of intracellular pH from acidosis. Furthermore, in rats treated with PPIs, pancreatic secretion was inhibited but concentrations of major ions in secretion follow similar excretory curves in control and PPI treated animals. In addition to HCO3 -, pancreas also secretes K+. In conclusion, this study calls for a revision of the basic model for HCO3 - secretion. We propose that proton transport is driving secretion, and that in addition it may provide a protective pH buffer zone and K+ recirculation. Furthermore, it seems relevant to re-evaluate whether PPIs should be used in treatment therapies where pancreatic functions are already compromised.

English

This case of ours is a 70year old male patient who presented with gastric outlet obstruction. Endoscopy revealed nodular ulcerated mass lesion involving 3/4 th of the circumference noted in the distal body of stomach along the incisura not involving pylorus and was subsequently diagnosed as gastric adenocarcinoma on endoscopic biopsy and for which distal gastrectomy was done. Histopathological sections showed well to moderately differentiated adenocarcinoma of stomach and sections from proximal duodenum showed lobules of brunner glands indicating a rare INTRODUCTION: Brunner's glands (or duodenal glands) are compound tubular submucosal glands found in that portion of the duodenum which is above the hepatopancreatic sphincter (Sphincter of Oddi). Brunner glands are localized predominantly in the submucosa of proximal duodenum that secrete alkaline fluid composed of muc in (MUC-6) which protects duodenal epithelium by counteracting the acid chyme from stomach. 1 Benign duodenal tumors are very rare with an estimated incidence of 0.008% reported in series of 215000 autopsies. 1 Brunner gland hyperplasia first described by swiss physician Johann Conrad brunner. The main function of these glands is to produce a mucus rich alkaline secretion in order to protect the duodenum from the acidic content of chyme (which is introduced into the duodenum from the stomach), provide an alkaline condition for intestinal enzymes, lubrication of intestinal walls and for better absorption. They also secrete urogastrone which inhibits parietal and chief cells of the stomach from

Slc26a3 deficiency is associated with loss of colonic HCO3− secretion, absence of a firm mucus layer and barrier impairment in mice

Downregulated in adenoma (DRA, Slc26a3) is a member of the solute carrier family 26 (SLC26), family of anion transporters, which is mutated in familial chloride-losing diarrhoea (CLD). Besides Cl(-) -rich diarrhoea, CLD patients also have a higher-than-average incidence of intestinal inflammation. In a search for potential explanations for this clinical finding, we investigated colonic electrolyte transport, the mucus layer and susceptibility against dextran sodium sulphate (DSS)-induced colitis in Slc26a3(-/-) mice. HCO3 (-) secretory (JHCO3 (-) ) and fluid absorptive rates were measured by single-pass perfusion in vivo and in isolated mid-distal colonic mucosa in Ussing chambers in vitro. Colonocyte intracellular pH (pHi ) was assessed fluorometrically, the mucus layer by immunohistochemistry and colitis susceptibility by the addition of DSS to the drinking water. HCO3 (-) secretory (JHCO3- ) and fluid absorptive rates were strongly reduced in Slc26a3(-/-) mice compared to wild-type (WT) littermates. Despite an increase in sodium/hydrogen exchanger 3 (NHE3) mRNA and protein expression, and intact acid-activation of NHE3, the high colonocyte pH in Slc26a3(-/-) mice prevented Na(+) /H(+) exchange-mediated fluid absorption in vivo. Mucin 2 (MUC2) immunohistochemistry revealed the absence of a firm mucus layer, implying that alkaline secretion and/or an absorptive flux may be necessary for optimal mucus gel formation. Slc26a3(-/-) mice were highly susceptible to DSS damage. Deletion of DRA results in severely reduced colonic HCO3 (-) secretory rate, a loss of colonic fluid absorption, a lack of a firmly adherent mucus layer and a severely reduced colonic mucosal resistance to DSS damage. These data provide potential pathophysiological explanations for the increased susceptibility of CLD patients to intestinal inflammation.

Protein phosphatase 1 coordinates CFTR‐dependent airway epithelial HCO3− secretion by reciprocal regulation of apical and basolateral membrane Cl−‐HCO3− exchangers

Our recent studies on human airway serous-like Calu-3 cells showed that cAMP agonists stimulated a HCO3(-) rich secretion containing up to 80 mM HCO3(-). This alkaline secretion relied on a coordinated switch in the activity of distinct Cl(-)-HCO3(-) anion exchangers (AE) located at different regions of the cell. At the apical membrane, cAMP agonists activated the electroneutral AE pendrin (SLC26A4), together with cystic fibrosis transmembrane conductance regulator (CFTR), while at the basolateral membrane the agonists inhibited AE2 (SLC4A2). However, the underlying mechanism(s) that orchestrates this cAMP-dependent switch in AE activity has not been elucidated. Apical and basolateral Cl(-)-HCO3(-) exchange was assessed by measuring Cl(-)-dependent changes in intracellular pH (pH(i)). We show that protein phosphatase 1 (PP1), together with CFTR, play central roles in this reciprocal regulation of AE activity. Activation of pendrin by cAMP agonists, but not inhibition of the basolateral exchanger, was protein kinase A-dependent. Knocking down CFTR expression, or blocking its activity with GlyH-101, led to incomplete inhibition of the basolateral AE by cAMP, supporting a role for CFTR in this process. Addition of the PP1/2A inhibitor, okadaic acid, but not the PP2A specific inhibitor fostreicin, mimicked the effect of cAMP stimulation. Furthermore, okadaic acid-treated Calu-3 monolayers produced a more alkaline fluid than untreated cells, which was comparable with that produced by cAMP stimulation. These results identify PP1 as a novel regulator of AE activity which, in concert with CFTR, coordinates events at both apical and basolateral membranes, crucial for efficient HCO3(-) secretion from Calu-3 cells.

Cholecystokinin but not ghrelin stimulates mucosal bicarbonate secretion in rat duodenum: Independence of feeding status and cholinergic stimuli

Cholecystokinin (CCK) is an important regulator of food digestion but its influence on small intestinal secretion has received little attention. We characterized effects of CCK-8, ghrelin and some related peptides on duodenal HCO3− secretion in vivo and demonstrated CCK-induced calcium signaling in acutely isolated enterocytes.A segment of proximal duodenum with intact blood supply was cannulated in situ in anaesthetized rats. Mucosal HCO3− secretion was continuously recorded (pH-stat). Peptides were administrated to the duodenum by close intra-arterial infusion. Clusters of duodenal enterocytes were attached to the bottom of a perfusion chamber. The intracellular calcium concentration ([Ca2+]i) was examined by dual-wavelength imaging.CCK-8 (3.0, 15 and 60 pmol/kg,h) caused dose-dependent increases (p<0.01) in duodenal alkaline secretion in both overnight fasted and continuously fed animals. The CCK1R-antagonist devazepide but neither the CCK2R-antagonist YMM022 nor the melatonin MT2-selective antagonist luzindole inhibited the rise in secretion. Atropine decreased sensitivity to CCK-8. The appetite-related peptide ghrelin was without effect on the duodenal secretion in fasted as well as fed animals. Superfusion with CCK-8 (1.0-50 nM) induced [Ca2+]i signaling in acutely isolated duodenal enterocytes. After an initial peak response, [Ca2+]i returned to near basal values within 3–5min. Devazepide but not YMM022 inhibited this [Ca2+]i response.Low doses of CCK-8 stimulate duodenal alkaline secretion and induce enterocyte [Ca2+]i signaling by an action at CCK1 receptors. The results point to importance of CCK in the rapid postprandial rise in mucosa-protective duodenal secretion.

Pancreatic Bicarbonate Secretion Involves Two Proton Pumps

Pancreas secretes fluid rich in digestive enzymes and bicarbonate. The alkaline secretion is important in buffering of acid chyme entering duodenum and for activation of enzymes. This secretion is formed in pancreatic ducts, and studies to date show that plasma membranes of duct epithelium express H(+)/HCO(3)(-) transporters, which depend on gradients created by the Na(+)/K(+)-ATPase. However, the model cannot fully account for high-bicarbonate concentrations, and other active transporters, i.e. pumps, have not been explored. Here we show that pancreatic ducts express functional gastric and non-gastric H(+)-K(+)-ATPases. We measured intracellular pH and secretion in small ducts isolated from rat pancreas and showed their sensitivity to H(+)-K(+) pump inhibitors and ion substitutions. Gastric and non-gastric H(+)-K(+) pumps were demonstrated on RNA and protein levels, and pumps were localized to the plasma membranes of pancreatic ducts. Quantitative analysis of H(+)/HCO(3)(-) and fluid transport shows that the H(+)-K(+) pumps can contribute to pancreatic secretion in several species. Our results call for revision of the bicarbonate transport physiology in pancreas, and most likely other epithelia. Furthermore, because pancreatic ducts play a central role in several pancreatic diseases, it is of high relevance to understand the role of H(+)-K(+) pumps in pathophysiology.

The impact of cyclooxygenase inhibition on duodenal motility and mucosal alkaline secretion in anaesthetized rats

Non-steroidal anti-inflammatory drugs (NSAIDs) are effective in the treatment of various human diseases. However, these drugs also have serious adverse effects in the gastrointestinal tract. In the duodenum NSAIDs inhibit mucosal alkaline secretion (DMAS), an important protective mechanism against the acid emptied from the stomach in most species, including humans. Surprisingly, NSAIDs have been shown to stimulate DMAS in an anaesthetized rat model. The aim of this review was to summarize the effects of NSAIDs and selective cyclooxygenase-2 (COX-2) inhibition on duodenal function in the rat and provide an explanation for why these drugs stimulate DMAS. Included are new data examining the effect of α-adrenergic drugs on duodenal motility and DMAS. Experiments were performed in anaesthetized rats. The proximal duodenum was perfused luminally with an isotonic NaCl solution. DMAS, motility, fluid flux and epithelial permeability were assessed in the absence and presence of various COX inhibitors. COX inhibition induced duodenal motility, increased DMAS and augmented the sensitivity as well as the maximal response of the duodenal mucosa to lidocaine- or hypotonicity-induced increases in mucosal permeability. Furthermore, the ability of the duodenum to absorb water and to adjust osmolality in response to luminal hypotonicity was improved in COX-inhibited animals. These improvements are mediated predominately via inhibition of COX-2. Inhibition of COX-2 in rats with postoperative duodenal ileus induces muscle contractions, which in turn activate a nicotinic receptor-dependent intramural reflex that stimulates duodenocytes to increase the activity of apical Cl⁻/HCO₃⁻ exchangers, resulting in a rise in DMAS.

Development of selective non-peptide angiotensin II type 2 receptor agonsists

The development of the first drug-like selective angiotensin II type 2 (AT(2)) receptor agonist (22) derived from the non-selective angiotensin II type 1 (AT( 1)) receptor/AT(2) receptor agonist L-162,313 is presented. Compound 22 with a K(i) value of 0.4 nM for the AT( 2) receptor and a K(i) > 10 microM for the AT(1) receptor induces outgrowth of neurite cells, stimulates p42/p44( mapk), enhances in vivo duodenal alkaline secretion in Sprague-Dawley rats and lowers the mean arterial blood pressure in anaesthetised spontaneously hypertensive rats. Thus, the peptidomimetic 22 exerts a similar biological response as the endogenous peptide angiotensin II after selective activation of the AT(2) receptor. In addition, Compound 22 has a bioavailability of 20-30% after oral administration and a half-life estimated to four hours in the rat. Compound 22 will therefore serve as a valuable research tool enabling studies of the function of the AT(2) receptor in more detail.

The past, present and future of angiotensin II type 2 receptor stimulation

Studying the angiotensin type 2 receptor (AT(2)) has been problematic in the past because a pharmacological tool for direct, specific in vitro and in vivo stimulation of the receptor has been lacking. Consequently, current knowledge about AT(2) receptor signalling and function had to be obtained by indirect approaches, like studying animals or cells with genetically altered AT(2) receptor expression levels, inhibitory experiments using specific AT(2) receptor antagonists, stimulation with angiotensin II under concomitant angiotensin II type 1 receptor blockade or stimulation with the peptide agonist CGP42112A, which has additional AT(2) receptor antagonistic properties. The recently developed non-peptide AT(2) receptor agonist Compound 21 now, for the first time, allows direct, selective and specific AT(2) receptor stimulation in vitro and in vivo. This new tool will certainly revolutionize AT(2) receptor research, enable many new insights into AT(2) receptor function and may also have the potential to become a future medical drug. This article reviews milestone findings about AT(2) receptor functional properties obtained by 'conventional' experimental approaches within the last 20 years. Moreover, it provides an overview of the first results obtained by direct AT(2) receptor stimulation with Compound 21, comprising effects on alkaline secretion, neurite outgrowth, blood pressure and post-infarct cardiac function.

Obscure Gastrointestinal Bleeding with Elusive Meckelʼs Diverticulum

Purpose: Obscure gastrointestinal tract bleeding can be particularly worrisome, as even after judicious testing, the etiology is not always certain. Meckel's diverticulum is a remnant of the viteline duct affecting about 2% of the population, making it the most prevalent congenital abnormality of the GI tract. It contains ectopic tissue of gastric and pancreatic predominance whose respective acidic and alkaline secretions can ulcerate tissue and cause hemorrhage. Around 90% of the diverticuli are within 90cm of the ileocecal valve. Results: 20-year-old healthy male with no past medical history was admitted for 4 episodes of painless rectal bleeding for one day. Slight nausea was present, but no emesis, fevers, abdominal pain or constitutional symptoms. No family history of colorectal cancer or IBD. Hemoglobin was 12.8. Colonoscopy showed blood throughout the entire colon and distal ileum, with ileal biopsy normal. EGD was unremarkable. Capsule endoscopy revealed small patches of hematin in distal intestine but no active bleeding source identified. There was no clear etiology of the bleeding and a presumed diagnosis of Dieulafoy's lesion was made. He was discharged and two days later, re-presented with continued rectal bleeding but was also severely anemic—hemoglobin 5.4. Colonoscopy and EGD was repeated showing blood throughout the colon and at the terminal ileum. Mesenteric angiogram showed no evidence of bleeding. Meckel's nuclear scan was performed showing no ectopic gastric mucosa. As the source of the rectal bleeding was not identified, exploratory laparotomy with push enteroscopy was performed, revealing an actively bleeding Meckel's diverticulum in the distal ileum along with suspected arteriovenous malformation in the distal jejunum. Diverticulectomy along with segmental small bowel resection was performed and afterwards bleeding resolved. Pathology confirmed Meckel's diverticulum with an ulceration extending into a submucosal artery. The acute anemia was treated with 10 units of RBC. Conclusion: Meckel's diverticulum is difficult to diagnose with nonspecific symptoms and can mimic a number of common conditions such as gastroenteritis, biliary colic, PUD, milk allergy, colonic diverticulitis. Complications include SBO, bleeding, intussusception and diverticulitis. CT scans are often nonspecific and arteriography is not always diagnostic because the arterial supply may not show any abnormalities. Technetium-99m scanning is the most useful test as it accumulates in gastric mucosa but sensitivity is only 62.5%, specificity 9%, in adults. This case illustrates the diagnostic importance of persistence in making a diagnosis of Meckel's diverticulum because of the insensitivity of current diagnostic modalities.

Small Bowel MRI Diagnosis of Meckelʼs Diverticulum

Purpose: Meckel's diverticulum (MD), occurring in 2% of the population, is the most common congenital abnormality of the GI tract. Small bowel MRI (SBMRI) is an emerging imaging modality that allows for transmural evaluation without ionizing radiation. We present a case of MD diagnosed by SBMRI. Methods: Case. Results: 17 year old man admitted with lower abdominal pain and maroon stools for the past evening. The patient reported a history of anemia but denied any previous bleeding. Physical examination revealed orthostatic hypotension, benign abdomen and red blood in rectal vault without hemorrhoids or fissures. Hemoglobin was 5.1 Gm/dl with iron deficiency, MCV-62fL and ferritin <15 nG/ml. Following volume resuscitation and blood transfusion- Tc-99m pertechnetate and bleeding scans were negative. EGD was normal. Colonoscopy displayed apthous ulcers in the ascending colon and terminal ileum with sparing of the cecum. Biopsy demonstrated changes consistent with Crohn's disease (CD). SBMRI, performed to evaluate extent of CD involvement, revealed a 6.7 cm diverticulum arising from the anti-mesenteric border of the distal small bowel (Figure).FigureConclusion: MD, a remnant of the omphalomesenteric duct, is typically diagnosed before age ten due to complicatons. Hemorrhage is the most common presentation of MD in children. Adults typically present with obstruction or diverticulitis. The lifetime risk of developing complications from MD is cited as 6%, and controversy exists whether this risk decreases with advancing age. Giant MD are greater than 6 cm in diameter. MD are composed of all layers of the ileal wall and heterotopic tissue is present in half of resected specimens. Gastric mucosa (GM) is found in 50% and panctreatic tissue (PT) in 5–16% of resected specimens. Acidic secretions from heterotopic GM and alkaline secretions from heterotopic PT result in mucosal ulceration. Tc-99m pertechnetate scan with a sensitivity of 75% is the best imaging modality for diagnosis. SBMRI has been advocated for evaluation of submucosal and serosal-mesenteric involvement of CD. Interestingly, a higher prevealence of MD in CD patients has been shown. SBMRI is a valuable addition in the diagnostic armamentarium for MD.

Propionate absorption associated with bicarbonate secretion in vitro in the mouse cecum

Short-chain fatty acids (SCFAs) produced by the microbial fermentation of undigested polysaccharide are rapidly absorbed in the large intestine. One proposed mechanism for this SCFA absorption is SCFA/HCO(-)3 exchange. To provide factual evidence for the operation of SCFA/HCO(-)3 exchange, we mounted an isolated mouse cecum in the Ussing chamber and measured the rates of propionate absorption (J(prop(ms))), alkaline secretion (J(OH(sm))) and total CO2 (HCO(-)3+CO2) secretion (J(tCO2(sm))), and the short-circuit current (I(sc)) with the mucosal side bathed with a Cl- and HCO(-)3-free solution. In the presence of propionate only on the mucosal but not in the serosal solution, J(prop(ms)) was larger when the serosal side was bathed with a HCO(-)3/CO2-containing solution than with a HCO(-)3/CO2-free solution. The addition of propionate to the mucosal side caused an increase in J(OH(sm)) and J(tCO2(sm)), the magnitude of these increases both being much greater with the serosal side bathed with the HCO(-)3/CO2-containing solution than with the HCO(-)3/CO2-free solution. Acetazolamide, a carbonic anhydrase inhibitor, largely suppressed HCO(-)3-dependent components of J(prop(ms)), propionate-induced J(OH(sm)), and propionate-induced J(tCO2(sm)). Acetazolamide, however, did not affect I(sc). The HCO(-)3-dependent component of J(prop(ms)) was not inhibited by either lactate or alpha-cyano-4-hydroxycinnamate, a typical substrate and an inhibitor of the monocarboxylate transporter (MCT1), respectively. It is concluded that an electroneutral, carbonic anhydrase-dependent SCFA/HCO(-)3 exchange mechanism was involved in SCFA absorption. The apical membrane protein for this pathway is not MCT1 and remains to be determined.

Serotonin increases protective duodenal bicarbonate secretion via enteric ganglia and a 5-HT4-dependent pathway

Objective. Serotonin (5-HT) is present in much larger amounts in the gut than in the central nervous system and is predominantly synthesized and stored in mucosal enterochromaffin cells. Bicarbonate secretion by the duodenal mucosa is the major mechanism in maintaining mucosal integrity, neutralizing invading protons within the surface mucus gel. In this study the role of local 5-HT in the control of the protective secretion was investigated. Material and methods. A segment of proximal duodenum was perfused in situ in anaesthetized rats and the alkaline secretion was continuously recorded by pH-stat. Intracellular calcium signalling was measured in clusters of human and rat duodenal enterocytes devoid of neural tissue. After loading with the fluorescent probe, fura-2, the clusters were attached to the bottom of a temperature-controlled perfusion chamber. Results. Close intra-arterial infusion to the duodenal segment of 5-HT (20–200 nmol kg−1 h−1) dose-dependently increased duodenal mucosal HCO3 secretion. A higher dose (2000 nmol kg−1 h−1) did not further increase secretion. Responses were inhibited by the ganglionic blocker and nicotinic receptor antagonist hexamethonium, and were abolished by the 5-HT4 receptor antagonist SB 204070. The 5-HT3 antagonist tropisetron, in contrast, caused only slight inhibition. Viable human and rat duodenal enterocytes responded to 5-HT (100–500 nM) with an increase in intracellular calcium concentration. Pretreatment with SB 204070 or removal of external calcium abolished the response. Conclusions. Stimulation of the duodenal protective secretion by 5-HT thus involves receptors of the 5-HT4 subtype as well as nicotinic transmission, the myenteric plexus being a likely location. In addition, serotonin acts on enterocyte membrane receptors, inducing intracellular calcium signalling.

Disruption of the SLC26A3-mediated anion transport is associated with male subfertility

Male subfertility in congenital chloride diarrhea (CLD) was possible after identification of expression of an epithelial Cl-/HCO3- exchanger SLC26A3 in the male reproductive tract and by the observation that adult men with CLD had very few children. A prospective clinical and laboratory study among eight adult Finnish men with CLD revealed constant oligoasthenoteratozoospermia but normal spermatogenesis, high chloride and low pH in seminal plasma, and three spermatoceles, suggesting that male subfertility is a clinical manifestation of CLD and could be caused by an analogous defect in the epithelial Cl-/HCO3- and water transport, as described for the CLD intestine.

Dynamic expression of the angiotensin II type 2 receptor and duodenal mucosal alkaline secretion in the Sprague–Dawley rat

Activation of angiotensin II type 2 receptors (AT2R) has been shown to stimulate duodenal mucosal alkaline secretion (DMAS) in Sprague-Dawley rats (S-D). This finding could not be confirmed in another line of S-D, and the present study investigates whether the level of AT2R expression determines the response to the AT2R agonist CGP42112A. DMAS was measured in anaesthetized rats using in situ pH-stat titration. Real-time PCR and Western blot were used to assess AT1R and AT2R RNA and protein expression, respectively. CGP42112A (0.1 microg kg(-1)min(-1) I.V.) elicited a 45% net increase in DMAS in the previous S-D line studied, whereas no change occurred in the new S-D line. Luminal administration of prostaglandin E2 (10(-5) M) increased DMAS similarly in both S-D lines. AT2R protein expression was significantly higher in tissue from the previous line compared to the new line. Individual AT1R to AT2R ratios (RNA and protein) were significantly higher in the new line compared to the previous S-D line. In the new S-D line intravenous infusion of angiotensin II (Ang II; 10 microg kg(-1) h(-1)) over 120 min significantly lowered the duodenal AT1aR to AT2R RNA ratio. Prolonged Ang II infusion over 240 min increased AT2R protein expression and evoked a 42% stimulatory response in DMAS to CGP42112A. The level of local AT2R expression determines the effect of the AT2R agonist CGP42112A on rat duodenal mucosal alkaline secretion. AT2R expression should be confirmed before interpreting the experimental effects of pharmacological interferences with this receptor.