No abstract

Background: The absorption of water and ions (especially Na+ and Cl−) is an important function of colonic epithelial cells in both physiological and pathophysiological conditions. Despite the comprehensive animal studies, there are only scarce available data on the ion transporter activities of the normal and inflamed human colon. Methods: In this study, 128 healthy controls and 69 patients suffering from ulcerative colitis (UC) were involved. We investigated the expressional and functional characteristics of the Na+/H+ exchangers (NHE) 1–3, the epithelial sodium channel (ENaC), and the SLC26A3 Cl−/HCO 3− exchanger downregulated in adenoma (DRA) in primary colonic crypts isolated from human biopsy and surgical samples using microfluorometry, patch clamp, and real‐time reverse‐transcription polymerase chain reaction (RT‐PCR) techniques. Results: Data collected from colonic crypts showed that the activities of electroneutral (via NHE3) and the electrogenic Na+ absorption (via ENaC) are in inverse ratio to each other in the proximal and distal colon. We found no significant differences in the activity of NHE2 in different segments of the colon. Surface cell Cl−/HCO 3− exchange is more active in the distal part of the colon. Importantly, both sodium and chloride absorptions are damaged in UC, whereas NHE1, which has been shown to promote immune response, is upregulated by 6‐fold. Conclusions: These results open up new therapeutic targets in UC. (Inflamm Bowel Dis 2011;)

The stimulatory pathways controlling HCO 3 Ϫ secretion by the pancreatic ductal epithelium are well described. However, only a few data are available concerning inhibitory mechanisms, which may play an important role in the physiological control of the pancreas. The aim of this study was to investigate the cellular mechanism by which substance P (SP) inhibits pancreatic ductal HCO 3 Ϫ secretion. Small intra/interlobular ducts were isolated from the pancreas of guinea pigs. During overnight culture the ducts seal to form a closed sac. Transmembrane HCO 3 Ϫ fluxes were calculated from changes in intracellular pH (measured using the pH-sensitive dye BCECF) and the buffering capacity of the cells. We found that secretin can stimulate HCO 3 Ϫ secretion in guinea pig pancreatic ducts about fivefold and that this effect could be totally blocked by SP. The inhibitory effect of SP was relieved by spantide, an SP receptor antagonist. SP had no effect on the activity of basolateral Na ϩ -HCO 3 Ϫ cotransporters and Na ϩ /H ϩ exchangers. However, the peptide did inhibit a Cl Ϫ -dependent HCO 3

In the colonic mucosa of patients with active UC, NHE3 transport capacity was found significantly decreased despite correct NHE3 location and abundance in the brush border, independent of current treatment. These findings suggest functional NHE3 transport as a novel factor for inflammatory diarrhea in UC patients.

It was shown for the first time that BK channels (i) are expressed at the apical membrane of guinea pig PDECs; (ii) have a crucial role in regulating HCO₃⁻ secretion and (iii) are also essential for the bile acid-induced hypersecretion and, therefore, underlie the response of the pancreas to this noxious agent.

Background: Deletion of phenylalanine-508 (ΔF508) from the first nucleotide-binding domain (NBD1) in the wild-type cystic fibrosis (CF) transmembrane-conductance regulator (wtCFTR) causes CF. However, the mechanistic relationship between ΔF508-CFTR and the diversity of CF disease is unexplained. The surface location of F508 on NBD1 creates the potential for protein-protein interactions and nearby, lies a consensus sequence (SYDE) reported to control the pleiotropic protein kinase CK2. Methods: Electrophysiology, immunofluorescence and biochemistry applied to CFTR-expressing cells, Xenopus oocytes, pancreatic ducts and patient biopsies. Results: Irrespective of PKA activation, CK2 inhibition (ducts, oocytes, cells) attenuates CFTR-dependent Cl^- transport, closing wtCFTR in cell-attached membrane patches. CK2 and wtCFTR co-precipitate and CK2 co-localized with wtCFTR (but not ΔF508-CFTR) in apical membranes of human airway biopsies. Comparing wild-type and ΔF508CFTR expressing oocytes, only ΔF508-CFTR Cl^- currents were insensitive to two CK2 inhibitors. Furthermore, wtCFTR was inhibited by injecting a peptide mimicking the F508 region, whereas the ΔF508-equivalent peptide had no effect. Conclusions: CK2 controls wtCFTR, but not ΔF508-CFTR. Others find that peptides from the F508 region of NBD1 allosterically control CK2, acting through F508. Hence, disruption of CK2-CFTR interaction by ΔF508-CFTR might disrupt multiple, membrane-associated, CK2-dependent pathways, creating a new molecular disease paradigm for deleted F508 in CFTR.

The potentially key role of visceral obesity in the association between perceived stress and dyslipidemia or diastolic blood pressure are discussed together with potential moderators (e.g. gender-differences, variations in stress assessment and metabolic syndrome criteria) that may explain the inconsistent, contradictory results of the individual studies.

Acinar and ductal cells of the exocrine pancreas form a close functional unit. Although most studies contain data either on acinar or ductal cells, an increasing number of evidence highlights the importance of the pancreatic acinar-ductal functional unit. One of the best examples for this functional unit is the regulation of luminal pH by both cell types. Protons co-released during exocytosis from acini cause significant acidosis, whereas, bicarbonate secreted by ductal cells cause alkalization in the lumen. This suggests that the first and probably one of the most important role of bicarbonate secretion by pancreatic ductal cells is not only to neutralize the acid chyme entering into the duodenum from the stomach, but to neutralize acidic content secreted by acinar cells. To accomplish this role, it is more than likely that ductal cells have physiological sensing mechanisms which would allow them to regulate luminal pH. To date, four different classes of acid-sensing ion channels have been identified in the gastrointestinal tract (transient receptor potential ion channels, two-pore domain potassium channel, ionotropic purinoceptor and acid-sensing ion channel), however, none of these have been studied in pancreatic ductal cells. In this mini-review, we summarize our current knowledge of these channels and urge scientists to characterize ductal acid-sensing mechanisms and also to investigate the challenge of the acinar acid load on ductal cells.