Modulation of rat pancreatic acinoductal transdifferentiation and expression of PDX-1 in vitro

AIMS/HYPOTHESIS

In adult pancreatic regeneration models exocrine acini are found to transdifferentiate to duct-like complexes. This has also been associated with the formation of new endocrine islet cells. We aimed to establish an in vitro model in which this transdifferentiation process is characterised and can be modulated.

METHODS

Purified rat pancreatic acini were cultured in suspension. Differentiation was analysed by immunocytochemistry, electron microscopy, western blotting and RT-PCR.

RESULTS

During culture acinar cells directly transdifferentiated without dividing, the cells lost their acinar phenotype and started to express cytokeratins 20 and 7 and fetal liver kinase-1 (Flk-1) receptors for vascular endothelial growth factor. Expression of the acinar pancreatic exocrine transcription factor (PTF-1) remained and the pancreatic duodenal homeobox-containing transcription factor (PDX-1) was induced. When transdifferentiation was completed, the cells started to express protein gene product 9.5, a panneuroendocrine marker. By combining these features, the transdifferentiated cells show similar characteristics to precursor cells during active beta-cell neogenesis. We were able to modulate the differentiation state by addition of nicotinamide or sodium butyrate, agents which are known to stimulate endocrine differentiation in other models.

CONCLUSION/INTERPRETATION

Here, we present an in vitro system in which the cellular differentiation of putative pancreatic endocrine precursor cells and their PDX-1 expression can be modulated, thereby providing a possible model for the study of beta-cell transdifferentiation.

Oral administration of a synthetic trypsin inhibitor increases pancreatic duct function in CCK-A receptor-deficient rats

The effects of oral administration of a synthetic trypsin inhibitor on bicarbonate secretion were examined in cholecystokinin A (CCK-A) receptor-deficient (OLETF) rats and compared with Wistar rats. Rats were fed chow containing 0.1% trypsin inhibitor for 7 days. Rats were prepared with cannulae draining bile and pancreatic juice separately and with duodenal and extrajugular vein cannulae after 3-day trypsin inhibitor ingestion. Then the animals were maintained in Bollman cages, and the experiments were conducted 4 days after surgery. After 1.5 h of basal secretion with bile-pancreatic juice return, bile-pancreatic juice was diverted for 2 h. The responses of bicarbonate secretion to bile-pancreatic juice diversion were significantly enhanced in rats treated with trypsin inhibitor compared with those given a control diet, whereas responses of fluid and protein secretion were not affected in OLETF rats. The response of protein secretion, but not those of fluid or bicarbonate secretion, was enhanced in Wistar rats by treatment with trypsin inhibitor. Carbonic anhydrase II gene expression was increased by 7-day treatment with trypsin inhibitor only in OLETF rats, and not in Wistar rats.

Purinoceptors evoke different electrophysiological responses in pancreatic ducts. P2Y inhibits K(+) conductance, and P2X stimulates cation conductance

In epithelia, extracellular nucleotides are often associated with regulation of ion transporters, especially Cl(-) channels. In this study, we investigated which purinoceptors are present in native pancreatic ducts and how they regulate ion transport. We applied whole-cell patch-clamp recordings, intracellular Ca(2+) and pH measurements, and reverse transcription-polymerase chain reaction (RT-PCR) analysis. The data show two types of purinoceptors and cellular responses. UTP and ATP produced large Ca(2+) transients, a decrease in intracellular pH, 8-10-mV depolarization of the membrane voltage, and a decrease in the whole-cell conductance. The membrane effects were due to closure of K(+) channels, as confirmed by dependence on extracellular K(+). UTP/ATP effects could be associated with P2Y(2) purinoceptors, and RT-PCR revealed mRNAs for P2Y(2) and P2Y(4) receptors. On the other hand, 2', 3'-O-4-benzoylbenzoyl-ATP induced Ca(2+) influx and approximately 20-mV depolarization of the membrane voltage with a concomitant increase in the whole-cell conductance. These effects were dependent on extracellular Na(+), not Cl(-), indicating opening of cation channels associated with P2X(7) purinoceptors. RT-PCR showed mRNAs for P2X(7) and P2X(4) receptors. In microperfused ducts, luminal (but not basolateral) ATP caused large depolarizations of membrane voltages recorded with microelectrodes, consistent with luminal localization of P2X(7) receptors. Thus, P2Y(2) (and possibly P2Y(4)) purinoceptors inhibit K(+) channels and may not support secretion in native ducts. P2X(7) (and possibly P2X(4)) receptors are associated with cation channels and may contribute to regulation of secretion.

Defective regulation of gap junctional coupling in cystic fibrosis pancreatic duct cells

The cystic fibrosis (CF) gene encodes a cAMP-gated Cl- channel (cystic fibrosis transmembrane conductance regulator [CFTR]) that mediates fluid transport across the luminal surfaces of a variety of epithelial cells. We have previously shown that gap junctional communication and Cl- secretion were concurrently regulated by cAMP in cells expressing CFTR. To determine whether intercellular communication and CFTR-dependent secretion are related, we have compared gap junctional coupling in a human pancreatic cell line harboring the DeltaF508 mutation in CFTR and in the same cell line in which the defect was corrected by transfection with wild-type CFTR. Both cell lines expressed connexin45 (Cx45), as evidenced by RT-PCR, immunocytochemistry, and dual patch-clamp recording. Exposure to agents that elevate intracellular cAMP or specifically activate protein kinase A evoked Cl- currents and markedly increased junctional conductance of CFTR-expressing pairs, but not in the parental cells. The latter effect, which was caused by an increase in single-channel activity but not in unitary conductance of Cx45 channels, was not prevented by exposing CFTR-expressing cells to a Cl- channel blocker. We conclude that expression of functional CFTR restored the cAMP-dependent regulation of junctional conductance in CF cells. Direct intercellular communication coordinates multicellular activity in tissues that are major targets of CF manifestations. Consequently, defective regulation of gap junction channels may contribute to the altered functions of tissues affected in CF.

Pancreatic islet cell survival following islet isolation: the role of cellular interactions in the pancreas

The purpose of this study was to characterize the trophic effect of pancreatic duct cells on the islets of Langerhans. Ductal epithelium and islets were isolated from hamster pancreata. In addition, duct-conditioned medium (DCM) was prepared from primary duct cultures that had been passaged twice to remove other cellular elements. Three experimental groups were then established: Group 1, 100 islets alone; Group 2, 100 islets+80 duct fragments; and Group 3, 100 islets in 25% DCM. All tissues were embedded in rat tail collagen for up to 12 days and the influence of pancreatic ductal epithelium on islet cell survival was examined. By day 12, 20.6+/-3. 0% (S.E.M.) of the islets cultured alone developed central necrosis, compared with 6.7+/-2.0% of the islets co-cultured with ducts and 5.6+/-1.5% of the islets cultured in DCM (P<0.05). The presence of apoptotic cell death was determined by a TdT-mediated dUTP-biotin nick end labelling (TUNEL) assay and by a specific cell death ELISA. DNA fragmentation in islets cultured alone was significantly increased compared with islets cultured either in the presence of duct epithelium or in DCM (P<0.05). More than 80% of TUNEL-positive cells were situated in the inner 80% of the islet area, suggesting that most were beta-cells. DCM was analysed for known growth factors. The presence of a large amount of IGF-II (34 ng/ml) and a much smaller quantity of nerve growth factor (4 ng/ml) was identified. When the apoptosis studies were repeated to compare islets alone, islets+DCM and islets+IGF-II, the cell death ELISA indicated that IGF-II produced the same beneficial result as DCM when compared with islets cultured alone. We conclude that pancreatic ductal epithelium promotes islet cell survival. This effect appears to be mediated in a paracrine manner by the release of IGF-II from cells in the ductal epithelium.

The homeodomain protein IDX-1 increases after an early burst of proliferation during pancreatic regeneration

Islet duodenal homeobox 1 (IDX-1/PF-1/STF-1/PDX-1), a homeodomain protein that transactivates the insulin promoter, has been shown by targeted gene ablation to be required for pancreatic development. After 90% pancreatectomy (Px), the adult pancreas regenerates in a process recapitulating embryonic development, starting with a burst of proliferation in the epithelium of the common pancreatic duct. In this model, IDX-1 mRNA was detected by semiquantitative reverse transcription-polymerase chain reaction in total RNA from isolated common pancreatic ducts at levels 10% of those of isolated islets. The IDX-1 mRNA levels were not significantly different for common pancreatic ducts of Px, sham Px, and unoperated rats and did not change with time after surgery. By immunoblot analysis, IDX-1 protein was only faintly detected in these ducts 1 and 7 days after Px or sham Px but was easily detected at 2 and 3 days after Px. Similarly, IDX-1 immunostaining was barely detectable in sham or unoperated ducts but was strong in ducts at 2-3 days after Px. The increase of IDX-1 immunostaining followed that of BrdU incorporation (proliferation). These results indicate a posttranscriptional regulation of the IDX-1 expression in ducts. In addition, islets isolated 3-7 d after Px showed higher IDX-1 protein expression than control islets. Thus, in pancreatic regeneration IDX-1 is upregulated in newly divided ductal cells as well as in islets. The timing of enhanced expression of IDX-1 implies that IDX-1 is not important in the initiation of regeneration but may be involved in the differentiation of ductal cells to beta-cells.

CFTR drives Na+-nHCO-3 cotransport in pancreatic duct cells: a basis for defective HCO-3 secretion in CF

Pancreatic dysfunction in patients with cystic fibrosis (CF) is felt to result primarily from impairment of ductal HCO-3 secretion. We provide molecular evidence for the expression of NBC-1, an electrogenic Na+-HCO-3 cotransporter (NBC) in cultured human pancreatic duct cells exhibiting physiological features prototypical of CF duct fragments (CFPAC-1 cells) or normal duct fragments [CAPAN-1 cells and CFPAC-1 cells transfected with wild-type CF transmembrane conductance regulator (CFTR)]. We further demonstrate that 1) HCO-3 uptake across the basolateral membranes of pancreatic duct cells is mediated via NBC and 2) cAMP potentiates NBC activity through activation of CFTR-mediated Cl- secretion. We propose that the defect in agonist-stimulated ductal HCO-3 secretion in patients with CF is predominantly due to decreased NBC-driven HCO-3 entry at the basolateral membrane, secondary to the lack of sufficient electrogenic driving force in the absence of functional CFTR.

Contribution of ductal cells to cytokine responses by human pancreatic islets

In type 1 diabetes, autoimmune destruction of pancreatic beta-cells has been attributed to cytokines released from infiltrating immunocytes. Exposure of isolated islets to cytokines leads to nitric oxide (NO) production, which can damage beta-cells. Because ductal cells are closely associated with human beta-cells, we examined whether they can contribute to this process. Isolated human ductal cells were cultured for 48 h with various cytokines. The combination of interleukin-1beta (IL-1beta) plus interferon-gamma (IFN-gamma) increased nitric oxide production 12-fold while stimulating mRNA expression of inducible nitric oxide synthase (iNOS). In this condition, 10-20% of cells positive for the cytokeratin-19 duct marker also stained positive for iNOS protein, whereas no positive cells were found in control preparations. Comparison of the magnitude of iNOS mRNA expression and nitric oxide production in these cells with that in isolated human islets suggests that >50% of total islet nitric oxide production might originate from associated ductal cells. It is concluded that ductal cells are a potential source of nitric oxide production in human islets infiltrated by cytokine-releasing immunocytes.

Induction of islet cell neogenesis in the adult pancreas: the partial duct obstruction model

The proliferative capacity of adult pancreatic islet cells is limited, although the formation of new islets from cells associated with the ductal epithelium is achievable even in the adult gland. Understanding the mechanism whereby proliferation and subsequent differentiation of putative precursor cells leads the appearance of new islets, i.e., islet neogenesis, may be important as a modality for treatment of both Type I and type II diabetes, in which there is an absolute or relative deficiency of insulin. It appears that certain genes and their protein products are essential to the initiation of the initial step in the pathway. We have shown that partial obstruction of the hamster pancreas is able to reverse streptozotocin-induced diabetes more than 50% of the time. An extract, termed ilotropin, prepared from obstructed pancreata, also reverses the diabetes, whereas extracts of control non-obstructed pancreata do not. Ilotropin contains a protein that is heat and acid stable with MW around 20-45 kDa that is capable of stimulating the proliferation of isolated duct cells in culture. Using mRNA and a differential display technique, 20 genes were found to be expressed in the partially obstructed (regenerating), but not the non-obstructed (non-regenerating) pancreas. One of these islet neogenesis-associated proteins (INGAP) proved to be unique to the obstructed pancreas, and a peptide contained within the sequence was capable of stimulating the proliferation of ductal cells in culture. INGAP was found to be expressed early in the neogenic process before the onset of ductal cell proliferation, and was capable of stimulating tritiated thymidine uptake into protodifferentiated epithelial cells, compatible with the notion that it might be involved in initiating the process of islet neogenesis.

Calcium-activated potassium conductances on cultured nontransformed dog pancreatic duct epithelial cells

Pancreatic duct epithelial cells (PDECs) mediate the pancreatic secretion of fluid and electrolytes. Membrane K+ channels on these cells regulate intracellular K+ concentration; in combination with the Na+/H+ antiport and Na+,K+ adenosine triphosphatase (ATPase), they may also mediate serosal H+ secretion, balancing luminal HCO3- secretion. We describe the K+ conductances on well-differentiated and functional nontransformed cultured dog PDECs. Through 86Rb+ efflux studies, we demonstrated Ca(2+)-activated K+ channels that were stimulated by A23187, thapsigargin, and 1-ethyl-2-benzimidazolinone, but not forskolin. These conductances also were localized on the basolateral membrane because 86Rb+ efflux was directed toward the serosal compartment. Of the K+ channel blockers, BaCl2, charybdotoxin, clotrimazole, and quinidine, but not 4-aminopyridine, apamin, tetraethylammonium, or iberiotoxin, inhibited 86Rb+ efflux. This efflux was not inhibited by amiloride, ouabain, and bumetanide, inhibitors of the Na+/H+ antiport, the Na+,K(+)-ATPase pump, and the Na+,K+,2Cl- cotransporter, respectively. When apically permeabilized PDEC monolayers were mounted in Ussing chambers with a luminal-to-serosal K+ gradient, A23187 and 1-ethyl-2-benzimidazolinone stimulated a charybdotoxin-sensitive short-circuit current (Isc) increase. Characterization of K+ channels on these cultured PDECs, along with previous identification of Cl- channels (1), further supports the importance of these cells as models for pancreatic duct secretion.

beta-Adrenergic regulation of ion transport in pancreatic ducts: patch-clamp study of isolated rat pancreatic ducts

BACKGROUND & AIMS

In the intact pancreas, bicarbonate secretion is thought to be controlled by a number of regulators, including adrenergic agonists. The aim of this study was to investigate the effects of adrenergic agonists on pancreatic ducts, which are the site of bicarbonate secretion.

METHODS

Small intralobular ducts were isolated from rat pancreas and studied in vitro by the whole-cell patch clamp technique. Cell membrane voltages and currents were indicators of cellular ion transport. In some ducts, intracellular Ca2+ activity was measured by fluorescence optical methods.

RESULTS

Unstimulated duct cells had a membrane voltage (Vm) of about -50 mV. Isoproterenol had a concentration-dependent effect on Vm; at 10(-7) mol/L, it depolarized Vm by 20-25 mV and the cell conductance increased by 100 nanosiemens. These effects were a result of opening of luminal Cl- channels. Phenylephrine had much smaller effects. At comparable concentrations, it depolarized Vm by a few millivolts. Neither agonist had significant effects on intracellular Ca2+.

CONCLUSIONS

This study provides the first direct evidence that adrenergic stimulation, namely, that of beta-adrenoceptors, controls ion transport in pancreatic ducts. Similar to secretin, isoproterenol stimulation leads to opening of luminal Cl- channels, and HCO3- enters the lumen in exchange for Cl-.

Secretory effects of ATP on nontransformed dog pancreatic duct epithelial cells

Extracellular triphosphate nucleotides, such as ATP, may regulate various cellular functions through specific cell surface receptors. We examine in this report the different secretory effects of ATP and analogs on nontransformed dog pancreatic duct epithelial cells (PDEC). We observed that 1) ATP, UTP, adenosine 5'-O-(3-thiotriphosphate), and, to a lesser extent, beta, gamma-methylene-ATP, but not adenosine, stimulated 125I- efflux from PDEC, suggesting a primary role for P2Y2 receptors, 2) ATP-stimulated 125I- efflux was inhibited by 5-nitro-2-(3-phenylpropylamino)benzoic acid, diphenylamine-2-carboxylate, and DIDS, suggesting mediation through Ca2+-activated Cl- channels, 3) ATP stimulated an 86Rb+ efflux sensitive to BaCl2 and charybdotoxin, thus likely occurring through Ca2+-activated K+ channels, 4) serosal or luminal addition of UTP activated apical Cl- conductance and basolateral K+ conductance when nystatin-permeabilized PDEC were studied in an Ussing chamber, suggesting the expression of P2Y2 receptors on both sides of the cell, 5) ATP stimulated mucin secretion, and 6) ATP increases intracellular Ca2+ concentration ([Ca2+]i). In conclusion, ATP and UTP interact with P2Y2 receptors on nontransformed PDEC to increase [Ca2+]i, stimulate mucin secretion, and activate ion conductances; these findings have implications for pancreatic exocrine function in both health and disease, such as cystic fibrosis.

Histamine stimulates ion transport by dog pancreatic duct epithelial cells through H1 receptors

Histamine affects pancreatic secretion, but its direct action on ion transport by pancreatic duct epithelial cells (PDEC) has not been defined. We now characterize the secretory effects of histamine on cultured, well-differentiated, and nontransformed dog PDEC. Histamine stimulated, in a concentration-dependent manner (1-100 microM), a cellular 125I- efflux that was inhibited by 500 microM 5-nitro-2-(3-phenylpropylamino)benzoic acid, 2.5 mM diphenylamine-2-carboxylate, and 500 microM DIDS and thus mediated through Ca2+-activated Cl- channels. Histamine-stimulated 125I- efflux was 1) inhibited by 100 microM diphenhydramine, an H1 receptor antagonist, 2) resistant to 1 mM cimetidine, an H2 receptor antagonist, 3) not reproduced by 1 mM dimaprit, an H2 agonist, and 4) inhibited by 50 microM 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid-AM, a Ca2+ chelator, suggesting that it was mediated through H1 receptors acting via increased cytosolic Ca2+. Histamine also stimulated a 86Rb+ efflux that was sensitive to 100 nM charybdotoxin and thus mediated through Ca2+-activated K+ channels. When PDEC monolayers were studied in Ussing chambers, a short-circuit current of 21.7 +/- 3.1 microA/cm2 was stimulated by 100 microM histamine. This effect was inhibited by diphenhydramine but not cimetidine, was not reproduced with dimaprit, and was observed only after serosal addition of histamine, suggesting that it was mediated by basolateral H1 receptors on PDEC. In conclusion, histamine, acting through basolateral H1 receptors, activates both Ca2+-activated Cl- and K+ channels; in this manner, it may regulate PDEC secretion in normal or inflamed pancreas.

Pancreatic juice and duodenal fluid flow rate in cow calves from birth to early ruminant state

The present investigation on pancreatic juice (PJ) and duodenal fluid (DF) was carried out in 10 crossbred (Jersey x Kankrej) male cow calves from birth to early ruminant state (15 week). The respective samples were measured in situ by cannulating the pancreatic duct and duodenal lumen, 30 minutes before feeding (BF) and 30 minutes after feeding (AF) both during morning (MH) and evening (EH). The results revealed significant increase in PJ and DF flow rate with age. Diurnal effect was nonsignificant except a significant increase recorded during EH on 4 d for PJ and 3 d for DF.

A new model for pancreatitis

Pancreatitis induced by ligation of the pancreatic duct produces morphologic similarities to human pancreatitis. This model is easily performed in big animals, but it is very difficult to perform pancreatic duct ligation in small animals. Many experimental studies of pharmaceutical treatments for pancreatitis used pancreatic duct-ligation models, but it is also difficult to evaluate the efficacy of the drugs used, because the animals used are of different species with individual differences. To overcome these problems, we ligated the main pancreatic duct of the splenic lobe by a 5.0 absorbable suture by using a surgical microscope and left the gastroduodenal lobe intact in the same rats. This model produced damaged pancreatic tissue in one part and normal pancreatic tissue in another part of the pancreas in the same animals, biochemically and histologically. We evaluated the effect of a new protease inhibitor (ONO-3404) on this preliminary model and found this new protease inhibitor demonstrated a hypertrophic effect on the damaged pancreatic tissue and the normal pancreatic tissue in the same animals. This model is also useful to study pharmaceutic treatment for pancreatic insufficiency and to study chemically induced pancreatic carcinogenesis in the damaged pancreatic tissue and the normal pancreatic tissue in the same animals.

Biliary, pancreatic, and sphincter of Oddi electrical and mechanical signals recorded during ERCP

Measurements of biliary tract motility have focused on radiologic and pressure measurements to quantify biliary motility rather than measurements of electrical activity of the biliary tract. We previously reported the recording of biliary electrical signals during ERCP and now report on the continued development and validation of a system to measure biliary tract electrical activity as well as biliary mechanical activity. In 26 patients presenting with a variety of clinical indications, we recorded measurements of electrical activity from the common bile duct sphincter (16 patients), pancreatic duct sphincter (eight patients), and/or sphincter of Oddi (eight patients). Electrical recordings were performed with a specially modified ERCP catheter, using two circular electrodes as well as a custom catheter that measured both electrical and mechanical activity. Electrical activity of the biliary tract was successfully recorded in 25 of 26 patients (96%), including the common bile duct sphincter (16 patients, 62%), pancreatic duct sphincter (eight patients, 31%) and sphincter of Oddi (eight patients, 31%). Along with the electrical recordings, common bile duct sphincter mechanical activity was recorded in 12 patients (67%), pancreatic duct sphincter mechanical activity in six patients (33%), and sphincter of Oddi mechanical activity in six patients (33%). Frequency analysis of electrical signals revealed a mean frequency (cycles/min) of 4.7 +/- 0.5 in the common bile duct sphincter, 4.1 +/- 0.6 in the pancreatic duct sphincter, and 4.9 +/- 0.7 in the sphincter of Oddi. Phasic mechanical frequency in cycles per minute was recorded at a frequency of 4.8 +/- 0.5 in common bile duct sphincter, 4.0 +/- 0.6 in pancreatic duct sphincter, and 5.3 +/- 0.9 in sphincter of Oddi. Tonic pressure (averaged 12.1 +/- 1.5 mm Hg) in common bile duct sphincter, 12.4 +/- 1.4 mm Hg in pancreatic duct sphincter, and 15.0 +/- 5.1 mm Hg in sphincter of Oddi. Analysis of wave form propagations (noted as percentage antegrade, retrograde, or indeterminant) revealed 50% antegrade, 23% retrograde, and 27% indeterminant). One patient was recorded on two occasions via ERCP; the same patient had an intraoperative recording. All three recordings showed similarities. We conclude that measurements of biliary, pancreatic, and sphincter of Oddi electrical and mechanical activity are feasible and can be done as part of ERCP. There was good correlation between biliary tract electrical and mechanical events and different wave form characteristics were noted for different parts of the biliary tree. Further studies are warranted to evaluate the potential usefulness of measurement of biliary tract electrical activity, and to confirm its correlation with mechanical events in the pancreato-biliary tree.

Role of cholecystokinin-A (CCK-A) receptor in pancreatic regeneration after pancreatic duct occlusion: a study in rats lacking CCK-A receptor gene expression

We examined the role of the cholecystokinin-A (CCK-A) receptor in acute inflammatory and regenerative stages of experimental pancreatitis using a rat model lacking the CCK-A receptor [Otsuka Long-Evans Tokushima Fatty (OLETF) rats]. OLETF and control [Long-Evans Tokushima Otsuka (LETO)] rats were prepared with an internal bile fistula and with obstruction of pancreatic flow and were sacrificed 1-14 days later. Histological examination was performed, and changes in pancreatic wet weight, protein concentration, CCK-A and -B receptor mRNA levels, tyrosine kinase activities, and plasma amylase and CCK levels were determined. The plasma amylase level showed a transient increase on day 1, the CCK level remained at high levels throughout, and tyrosine kinase activity was increased significantly on day 3 but declined thereafter. These parameters were comparable for both strains during the acute inflammatory stage. However, no regenerative findings were observed by histological examination and the protein concentration in the pancreas was significantly lower in OLETF rats on days 7-14, during which time regeneration was completed in LETO rats. These observations indicate that the absence of the CCK-A receptor did not modify the acute phase of pancreatitis but significantly retarded regeneration of the pancreatic tissue.

Intermediate endocrine-acinar pancreatic cells in duct ligation conditions

When tissues were subjected to 24 h of duct ligation, intermediate pancreatic cells simultaneously displaying endocrine and exocrine phenotypes appeared. Immunocytochemistry by laser scanning confocal microscopy revealed the appearance of a large number of these cells coexpressing insulin and amylase. These cells were located within the islets of Langerhans as well as in the acinar parenchyma. They were also detected in a culture system of isolated pancreatic cells. With the use of immunoelectron microscopy, two types of secretory granules were identified in these cells. One was insulin immunoreactive, whereas the other, resembling zymogen granules, contained amylase. Occasionally, some small granules displayed a double labeling for both secretory proteins. Numerous crinophagic bodies and autophagosomes containing insulin and/or amylase were also present. In situ hybridization, applied with the specific probes, confirmed the presence of both insulin and amylase mRNAs in these cells. Because duct ligation is known to induce insulin cell proliferation, the present results confirm that endocrine-acinar cells do appear in such condition and may represent intermediate steps in a transdifferentiating process.

Long-term duct-occluded segmental pancreatic autografts: absence of microvascular diabetic complications

BACKGROUND

Current insulin therapies for control of glucose metabolism in patients with type I diabetes mellitus prevent major metabolic consequences of insulin deficiency, but none prevents or arrests long-term complications. In experimental models of canine diabetes, retinopathy, neuropathy, and nephropathy have been shown to develop within 5 years. The aim of this study was to determine in a canine model whether glucose control provided by segmental duct-occluded pancreas autografts could prevent the long-term complications of diabetes.

METHODS

Thirty-five outbred mongrel dogs underwent segmental pancreas autotransplantation with residual pancreatectomy. Follow-up over 5 years included endocrine, retinal fundus photography, fluorescein angiography, and nerve conduction studies. At endpoint, analysis of organ specific changes was undertaken.

RESULTS

Long-term survival was achieved in 14 dogs for 4 to 5 years and in 3 dogs for 3 to 5 years. Glycosylated hemoglobin levels remained within normal limits, although response to glucose challenge was suboptimal. Fundus photography and fluorescein angiography demonstrated the absence of retinal vascular aneurisms, capillary leakage, and obliteration. Retinal digest showed no vascular changes and normal endothelial/pericyte ratios. Nerve conduction was normal, and histology of nerves revealed normal density of myelinated fibers and absence of intrafascicular vessels and glycogen deposits, with no change in spectrum of fiber diameters and ovoids. Renal histology revealed no evidence of nephropathy with normal glomerular basement membranes.

CONCLUSIONS

We have demonstrated that duct-occluded segmental pancreatic autografts are capable of providing satisfactory metabolic control for up to 5 years, thereby preventing development of the long-term microvascular complications of diabetes.

Intercalated duct cells in the chicken pancreatic islet

Intercalated duct cells are present in the alpha and beta islets of the chicken pancreas. The intercalated duct cells adhere to each other via intercellular junctional complexes at the apical side, projecting many microvilli and a few of cilia into the lumen. Abluminally, these cells extend slender cytoplasmic processes between islet endocrine cells. These intercalated duct cells appear to have a stellate form, and to wrap around endocrine cells with their cytoplasm. These observations suggest that intercalated ducts not only pass through the islet, but also play a role in supplying islet cells.

The pancreatic duct epithelium in vitro: bile acid injury and the effect of epidermal growth factor

BACKGROUND

Pancreatic duct epithelial cells form a barrier against parenchymal injury. The capacity of these cells to respond to injury has not been investigated. We hypothesized that epidermal growth factor (EGF), normally found in pancreatic juice, could protect the duct epithelium from damage.

METHODS

An explant system of duct cell culture developed in our lab with the bovine main pancreatic duct was used. Explants were exposed to bile acid (taurodeoxycholic acid [TDCA] 0, 0.05, 0.5, and 1 mmol/L) in the presence or absence of EGF (0, 1, 10, and 100 nmol/L) for 48 hours. Epithelial proliferation, damage, and growth out from the explant edge were assessed histologically. Expression of ductal markers and the extent of cell proliferation were determined by immunohistochemistry using specific antibodies.

RESULTS

Explant duct cells proliferated and demonstrated continued expression of key duct antigens in culture. TDCA produced dose-dependent mucosal damage and reduced epithelial density and growth from the edge. EGF increased cellular density in the native epithelium, but did not significantly alter growth from the edge. Mucosal damage created by TDCA exposure was significantly decreased with EGF and both growth from the edge and cell density were preserved.

CONCLUSIONS

Explants created from the bovine main pancreatic duct serve as an excellent model for the study of duct epithelial cells in vitro. These cells proliferate in response to EGF and are damaged by TDCA at concentrations below those normally associated with detergent-like activity and below levels observed in bile and duodenal secretions. The ability of EGF to protect from this injury suggests a potential physiologic role in the maintenance of the pancreatic duct mucosal barrier.

Bovine pancreatic duct cells express cAMP- and Ca(2+)-activated apical membrane Cl- conductances

Secretion of salt and water by the epithelial cells that line pancreatic ducts depends on activation of apical membrane Cl- conductance. In the present study, we characterized two types of Cl- conductances present in the apical cell membrane of bovine pancreatic duct epithelial cells. Primary cultures of bovine main pancreatic duct epithelium and an immortalized cell line (BPD1) derived from primary cultures were used. Elevation of intracellular adenosine 3',5'-cyclic monophosphate (cAMP) or Ca2+ in intact monolayers of duct epithelium induced sustained anion secretion. Agonist-induced changes in plasma membrane Cl- permeability were accessed by 36 Cl- efflux, whole cell current recording, and measurements of transepithelial Cl- current across permeabilized epithelial monolayers. Elevation of intracellular cAMP elicited a sustained increase in Cl- permeability, whereas elevation of intracellular Ca2+ induced only a transient increase in Cl- permeability. Ca(2+)- but not cAMP-induced increases in Cl- permeability were abolished by preincubation of cells with the Ca2+ buffer 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid, tetra(acetoxymethyl) ester (BAPTA-AM). N-phenylanthranilic acid (DPC; 1 mM) and glibenclamide (100 microM), but not 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS; 500 microM), inhibited the cAMP-induced increase in Cl- permeability. In contrast, DPC and DIDS, but not glibenclamide, inhibited the Ca(2+)-induced increase in Cl- permeability. We conclude from these experiments that bovine pancreatic duct epithelial cells express at least two types of Cl- channels, cAMP and Ca2+ activated, in the apical cell membrane. Because the Ca(2+)-activated increase in Cl- permeability is transient, the extent to which this pathway contributes to sustained anion secretion by the ductal epithelium remains to be determined.

[The ultrasonic diagnosis of the phasic interdigestive activity of the pancreas and the main pancreatic duct in healthy subjects and chronic pancreatitis patients]

Sixteen healthy subjects and 113 patients with chronic pancreatitis were studied for ultrasonic dynamics of phase interdigestive activity of pancreas and calibre of the main pancreatic duct (MPD). Both in healthy individuals and patients, the gland sizes and MPD calibre change with phases of interdigestive motility of duodenum. The largest sizes in healthy subjects are found in phase 2 irregular contractions of duodenum, the least ones--in patients with grave disease course. This is an important differential and diagnostic criterion between chronic pancreatitis and normal functional state of pancreas corresponding to a certain phase of interdigestive motility of duodenum. Phase-dependent sizes of pancreas and MPD calibre are to be taken into account in conducting ultrasonography of pancreas and interpretation of the results obtained.

Isolation and culture of bovine pancreatic duct epithelial cells

We describe a method to isolate and culture epithelial cells from the main duct of the bovine pancreas. In primary cultures, secretin caused a dose-dependent increase in intracellular adenosine 3',5'-cyclic monophosphate (cAMP) and stimulated electrogenic transepithelial ion transport. Elevation of intracellular cAMP increased the rate coefficient for 36Cl- efflux from 0.14 +/- 0.03 to 0.47 +/- 0.12 min-1, and plasma membrane conductance, measured by the whole cell patchclamp technique, was increased from 0.7 +/- 0.1 to 6.9 +/- 0.8 nS. The cAMP-activated anion currents had properties similar to those mediated by the cystic fibrosis transmembrane conductance regulator (CFTR) protein. Cells grown on permeable supports formed confluent monolayers with high transepithelial electrical resistance (1.004 +/- 96 omega. cm2) and generated a lumen negative transepithelial voltage difference (-2.5 +/- 0.6 mV). The short-circuit current (Isc) was increased by forskolin or secretin and was inhibited 87 +/- 4% by addition of ouabain (100 microM) to the basolateral bathing solution. Replacement of bathing solution Cl- by cyclamate reduced the forskolin-induced steady-state increase in Isc from 5.3 +/- 0.5 to 0.2 +/- 0.2 microA/cm2, suggesting that the stimulated current is due to anion secretion. The results of these studies demonstrate that large numbers of pancreatic ductal cells can be isolated and grown in primary cell culture. The monolayers express differentiated functions and will be useful for studies of acute and chronic regulation of ion transport in pancreatic duct epithelial cells.