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A Na(+)/HCO(3)(-) cotransporter (NBC) is located in the basolateral membrane of the gastrointestinal epithelium, where it imports HCO(3)(-) during stimulated anion secretion. Having previously demonstrated secretagogue activation of NBC in murine colonic crypts, we now asked whether vesicle traffic and exocytosis are involved in this process. Electrogenic NBCe1-B was expressed at significantly higher levels than electroneutral NBCn1 in colonic crypts as determined by QRT-PCR. In cell surface biotinylation experiments, a time-dependent increase in biotinylated NBCe1 was observed, which occurred with a peak of +54.8% after 20 min with forskolin (P < 0.05) and more rapidly with a peak of +59.8% after 10 min with carbachol (P < 0.05) and which corresponded well with the time course of secretagogue-stimulated colonic bicarbonate secretion in Ussing chamber experiments. Accordingly, in isolated colonic crypts pretreated with forskolin and carbachol for 10 min, respectively, and subjected to immunohistochemistry, the NBCe1 signal showed a markedly stronger colocalization with the E-cadherin signal, which was used as a membrane marker, compared with the untreated control. Cytochalasin D did not change the observed increase in membrane abundance, whereas colchicine alone enhanced NBCe1 membrane expression without an additional increase after carbachol or forskolin, and LY294002 had a marked inhibitory effect. Taken together, our results demonstrate a secretagogue-induced increase of NBCe1 membrane expression. Vesicle traffic and exocytosis might thus represent a novel mechanism of intestinal NBC activation by secretagogues.

Key points• The mucosa of the proximal duodenum is regularly exposed to the strong acid of gastric juice, and acid damage causes peptic ulceration and bleeding.• The epithelial cells of the duodenum protect themselves against acid-induced chemical damage by secreting bicarbonate into the lumen and by regulating their intracellular pH, but the molecular mechanisms of duodenal pH i control are incompletely understood.• We have found a high expression of the electroneutral sodium bicarbonate transporter Slc4a7 (NBCn1) in the basolateral membrane of duodenal villous enterocytes.• Genetic knockout of Slc4a7 resulted in a strong defect in duodenocyte pH i recovery from acid loads, and reduced bicarbonate secretory rates.• This suggests that the electroneutral sodium bicarbonate cotransporter Slc4a7 is a major import mechanism for HCO 3 − from the blood into the duodenal epithelial cells. Defects in this transporter may severely endanger duodenal mucosal integrity Abstract Duodenocyte pH i control and HCO 3 − secretion protects the proximal duodenum against damage by gastric acid. The molecular details of duodenocyte pH control are not well understood. A selective duodenal expression (within the upper GI tract) has been reported for the electroneutral Na + :HCO 3 − cotransporter NBCn1 (Slc4a7). We aimed to determine the role of NBCn1 and NBCe2 in duodenocyte intracellular pH regulation as well as basal and agonist-stimulated duodenal bicarbonate secretion (J HCO3 − ), exploiting mouse models of genetic slc4a7 and slc4a5 disruption. Basal and forskolin (FSK)-stimulated J HCO3 − was measured by single-pass perfusion in the duodenum of slc4a7 −/− and slc4a7 +/+ as well as slc4a5 −/− and slc4a5 +/+ mice in vivo, and by pH-stat titration in isolated duodenal mucosa in vitro. Duodenocyte HCO 3 − uptake rates were fluorometrically assessed after acidification of intact villi and of isolated duodenocytes. Slc4a7 −/− mice displayed significantly lower basal and FSK-stimulated duodenal HCO 3 − secretion than slc4a7 +/+ littermates in vivo. FSK-stimulated HCO 3 − secretion was significantly reduced in slc4a7 −/− isolated duodenal mucosa. Na + -and HCO 3 − -dependent base uptake rates were significantly decreased in slc4a7 −/− compared with slc4a7 +/+ villus duodenocytes when measured in intact villi. Carbonic anhydrase (CA)-mediated CO 2 hydration played no apparent role as a HCO 3 − supply mechanism for basal or FSK-stimulated secretion in the slc4a7 +/+ duodenum, but was an important alternative HCO 3 − supply mechanism in the slc4a7 −/− duodenum. NBCe2 (Slc4a5) displayed markedly lower duodenal mRNA expression levels, and its disruption did not interfere with duodenal HCO 3 − secretion.

Podocyte loss is a common feature in human diabetes as well as in experimental diabetes in rodents. Almost all components of the diabetic milieu lead to serious podocyte stress, driving the cells towards cell cycle arrest and hypertrophy, detachment and apoptosis. Common pathway components induced by high glucose and advanced glycation end-products are reactive oxygen species, cyclin-dependent kinases (p27(Kip1)) and transforming growth factor-beta. In addition, mechanical stresses by stretch or shear forces, insulin deficiency or insulin resistance are independent components resulting in podocyte apoptosis and detachment. In this review, we discuss the common pathways leading to podocyte death as well as novel pathways and concepts of podocyte dedifferentiation and detachment that influence the progression of diabetic glomerulopathy.

Zusammenfassung Ergebnisse Bei den Steinen handelte es sich um Struvit (44,7 %), Kalziumoxalat-Monohydrat (Whewellit, 24,5 %), Cystin (15,2 %), Ammoniumurat (5,3 %), Kalziumoxalat-Dihydrat (Weddellit, 4,4 %), Kalziumphosphat (1,6 %), Xanthin (1,2 %), Whewellit/Weddellit (1,1 %), Brushit (0,4 %) und andere Substanzen 1,7 %. Das mediane Alter (Jahre) der Hunde betrug bei Struvit 8, bei Kalziumoxalaten (Whewellit und Weddellit) 10, bei Cystin 5, bei Brushit 11, bei Xanthin 6,5 und bei Ammoniumurat 6. Bei weiblich-intakten (83,8 %) und weiblich-kastrierten (80,8 %) Individuen kamen Struvitsteine am häufigsten vor, während bei männlich-intakten Hunden Cystinsteine (36,7 %) und Kalziumoxalate (35,5 % Whewellit und Weddellit) dominierten. Kastrierte Rüden hatten zu 50,0 % Kalziumoxalat, zu 17,3 % Struvit und zu 10,5 % Cystinsteine. Struvitsteine ließen sich am häufigsten bei den Rassen Mops (75,9 %), Labrador (73,1 %), Shih Tzu (62,2 %), Dackel (50,4 %) und Malteser (36 %) nachweisen, Kalziumoxalate bei den Rassen Zwergschnauzer (54,8 %), Jack Russell Terrier (49,5 %) sowie Yorkshire Terrier (48,2 %). Cystin trat am häufigsten bei den Rassen Französische Bulldogge (47,2 %), Bulldogge (44,8 %), Chihuahua (44,1 %) und Dackel (32,8 %) auf. Schlussfolgerung und klinische Relevanz Hunde aus Deutschland zeigten alters-, geschlechts- und rassespezifische Unterschiede in der Häufigkeit des Auftretens von Harnsteinen. Die Kenntnis über ein gehäuftes Vorkommen unterschiedlicher Harnsteinarten in Deutschland sowie über eine mögliche Rassedisposition ermöglicht dem Tierarzt, ein zielgerichtetes Monitoring zur Prophylaxe und Metaphylaxe zu etablieren und gemeinsam mit dem Tierbesitzer einen geeigneten Therapieplan zu erstellen.

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