A new, rapid, method for preparation of dispersed pancreatic acini

In vitro secretion of zymogens by bovine pancreatic acini and ultra-structural analysis of exocytosis

The aim of this study is to establish a bovine pancreatic acinar cell culture model with longer viability and functionality. The cells could be maintained in a functional state for upto 20 days with normal morphology. Cells were positive for amylase as observed by immunofluorescence staining. Acinar cells are spherical and range about 2–3 µm in diameter. The porosome formed by exocytosis and heterogenous enzyme granules of size ranging 100–300 nm were seen on the surface of cells by electron microscopy. The activity of the enzymes was high on day 15 and the activity profile of the enzymes is in the order: protease>lipase>amylase and the enzymes were identified by SDS-PAGE. Long-term culture of bovine pancreatic acini could be useful in studying the pathogenesis of pancreatitis. Since the bovine genome shares about 80% identity with the human genome, the cells derived from bovine pancreas can be engineered and used as a potential xenotransplant to treat conditions like pancreatitis as the tissue source is abundantly available.

•

Acinar cells are functional unit of pancreas.

•

In vitro release of enzyme granules by exocytosis are well demonstrated.

•

Amylase shares 86% protein identity with that of human.

•

Acinar culture showed longer viability upto 20 days with normal cellular function.

•

Useful culture model in understanding the acinar cell biology and physiology.

Role of neutrophils in the activation of trypsinogen in severe acute pancreatitis

The relationship between inflammation and proteolytic activation in pancreatitis is an unresolved issue in pancreatology. The purpose of this study was to define the influence of neutrophils on trypsinogen activation in severe AP. Pancreatitis was induced by infusion of taurocholate into the pancreatic duct in C57BL/6 mice. For neutrophil depletion, an anti-Gr-1 antibody was administered before pancreatitis induction. Administration of the anti-Gr-1 antibody reduced circulating neutrophils by 97%. Pancreatic TAP and serum amylase levels increased 2 h and 24 h after induction of pancreatitis. Neutrophil depletion reduced pancreatic TAP and serum amylase levels at 24 h but not at 2 h after pancreatitis induction. Pancreatic MPO and infiltration of neutrophils, as well as MIP-2 levels, were increased 24 h after taurocholate infusion. Two hours after taurocholate administration, no significant pancreatic infiltration of neutrophils was observed. Injection of the anti-Gr-1 antibody abolished MPO activity, neutrophil accumulation, and MIP-2 levels, as well as acinar cell necrosis, hemorrhage, and edema in the pancreas at 24 h. Moreover, taurocholate-provoked tissue damage and MPO activity in the lung were normalized by neutrophil depletion. Intravital fluorescence microscopy revealed a 97% reduction of leukocytes in the pancreatic microcirculation after administration of the anti-Gr-1 antibody. Our data demonstrate that initial trypsinogen activation is independent of neutrophils, whereas later activation is dependent on neutrophils in the pancreas. Neutrophils are critical in mediating pancreatic and lung tissue damage in severe AP.

Mitochondrial dysfunction and apoptosis of acinar cells in chronic pancreatitis

BACKGROUND

The mechanism of acinar cell death in human chronic pancreatitis (CP) remains largely unexplored. Previous studies have demonstrated the role played by apoptosis and necrosis in experimental pancreatitis; however, their relationship with the progression of CP remains unknown. The present study was carried out to elucidate the role and extent of apoptosis in CP tissues with different histopathological scores and to examine the possible apoptotic pathway involved.

METHODS

Pancreatic tissues (25 CP patients) that had been histopathologically graded (I-III) and ten normal pancreatic tissue samples were evaluated for apoptosis by DNA fragmentation and an in situ TUNEL assay. The expression of various apoptotic and antiapoptotic markers in the tissues were studied by immunohistochemistry and Western blotting. To elucidate the role of the mitochondria in acinar cell death, the mitochondrial membrane potential (DeltaPsim) and ATP levels were determined by flow cytometry and a luminometer.

RESULTS

The presence of DNA fragmentation and apoptotic nuclei in all CP tissues confirmed the presence of apoptosis. The apoptotic index in CP tissue ranged from 0.09% to 0.86% +/- 0.02% and was highest in grade II (0.7 +/- 0.04%) tissues. Differential upregulation of the apoptotic mediators p53, Bax, cytochrome c, and caspase-3 and -9, and downregulation of antiapoptotic Bcl-2, was observed in CP. DeltaPsim on the order of 1.2-to 2.2-fold and ATP depletion in the range of 23%-84% in CP tissues was observed.

CONCLUSIONS

Apoptosis plays an important role both in the initial stages and during the progression of CP, as evident in all tissue grades. Increased DeltaPsim, loss of ATP, and activation of caspases suggests the involvement of intrinsic pathways.

Primary culture of pancreatic (human) acinar cells

The acinar cell culture plays a very important role in research of pancreatic pathophysiology. The aim of this study was to establish a long-term culture of human (foetal) pancreatic acinar cells in standardized nutrient media with supplements. Acinar cells were prepared from pancreatic tissues obtained from aborted foetus (> or =35 weeks) with no prior pancreatic complications by collagenase digestion and cultured using different media and supplements. The purity and phenotype of acinar cells was confirmed by various staining techniques and FACS. The acinar cell proliferation was determined at different time intervals by Bromo-deoxyuridine (BrdU) incorporation, and metabolic enzyme activity was analysed. The acini could be cultured and maintained in Ham's F-12 K/M199 media in the presence of 5% BSA, 0.1 mg/ml STI, 10 ng/ml EGF, and 10% FCS with the same morphological appearance as that of freshly prepared for 12 days with maximum viability of 80-85% and formation of monolayer without extracellular matrix. A significant BrdU incorporation of acinar cells in primary culture was observed which was maximum (105%) at day four. Higher amylase and lipase activity was seen in freshly isolated acinar cells which decreased with time of the culture. The established human pancreatic acinar cell culture may act as an excellent model to study exocrine dysfunction or pancreatitis in response to acinar cell injury.

Prostaglandin E2 modulates TNF-alpha-induced MCP-1 synthesis in pancreatic acinar cells in a PKA-dependent manner

Cyclooxygenase (COX)-2 is increased in human chronic pancreatitis. We recently demonstrated in a model of chronic pancreatitis (WBN/Kob rat) that inhibition of COX-2 activity reduces and delays pancreatic inflammation and fibrosis. Monocyte chemoattractant protein (MCP)-1 mRNA and PGE(2) were significantly reduced, correlating with a decreased infiltration of macrophages. MCP-1 plays an important role in the recruitment of macrophages to the site of tissue injury. The aim of our study is to identify mechanisms by which macrophages and acinar cells maintain an inflammatory reaction. The expression profile of E prostanoid receptors EP(1-4) and MCP-1 was analyzed by RT-PCR from pancreatic specimens and AR42J cells. MCP-1 secretion was detected by ELISA from rat pancreatic lobuli. We determined EP(1-4) mRNA levels in WBN/Kob rats with chronic pancreatic inflammation. Individual isoforms were highly increased in rat pancreas, concurrent with MCP-1 mRNA expression. In supernatants of pancreatic lobuli and AR42J cells, MCP-1 was detectable by ELISA. In the presence of TNF-alpha, MCP-1 was upregulated. Coincubation with PGE(2) enhanced the TNF-alpha-induced MCP-1 synthesis significantly. Similarly, TNF-alpha mRNA was synergistically upregulated by TNF-alpha and PGE(2). Furthermore, the synergistic effect of TNF-alpha and PGE(2) was abolished by inhibition of PKA but not of PKC. We conclude that EP receptors are upregulated during chronic pancreatic inflammation. PGE(2) modulates the TNF-alpha-induced MCP-1 synthesis and secretion from acinar cells. This synergistic effect is controlled by PKA. This mechanism might explain the COX-2-dependent propagation of pancreatic inflammation.

Intracellular activation of trypsinogen in rat pancreatic acini after supramaximal secretagogue stimulation: cysteine protease and serine protease activity

OBJECTIVE

The aim of the study was to explore the mechanism by which trypsinogen becomes activated during acute pancreatitis.

METHODS

Given the ability of cholecystokinin (CCK) to induce pancreatitis in vivo, the effects of high-dose CCK on preparations of isolated pancreatic acini were examined using immunofluorescence techniques for the detection of trypsinogen activation. Acini were pretreated with weak base or serine or cysteine protease inhibitors before CCK hyperstimulation.

RESULTS

CCK was found to stimulate the generation of trypsinogen activation peptide (TAP), a marker for trypsinogen processing. The generation of TAP was inhibited by pretreatment with a weak base, chloroquine (40 micromol/L). TAP generation was also inhibited by pretreatment with serine protease inhibitor FUT-175 (1 micromol/L) but not cysteine protease inhibitor E64 (0.1 mmol/L) or E64-d (0.1 mmol/L). Although treatment with a high dose of E64-d (1 mmol/L) reduced activation, it also caused cell injury.

CONCLUSIONS

High-dose CCK stimulated the intracellular activation of trypsinogen within isolated pancreatic acini. This event appears to require an acidic subcellular compartment and serine protease activity. The role for thiol proteases in this model remains unclear.

Protein tyrosine phosphatase kappa and SHP-1 are involved in the regulation of cell-cell contacts at adherens junctions in the exocrine pancreas

BACKGROUND

We have previously shown that cell contacts between pancreatic acinar cells dissociate early in pancreatitis and that this is a prerequisite for the development of pancreatic oedema. Here we studied the underlying mechanism.

METHODS

Employing experimental caerulein induced pancreatitis in vivo and isolated pancreatic acini ex vivo, in conjunction with protein chemistry, morphology, and electron microscopy, we determined whether cell contact regulation in the pancreas requires or involves: (1) changes in cadherin-catenin protein expression, (2) tyrosine phosphorylation of adhesion proteins, or (3) alterations in the actin cytoskeleton.

RESULTS

During initial cell-cell contact dissociation at adherens junctions, expression of adhesion proteins remained stable. At time points of dissociated adherens junctions, the cadherin-catenin complex was found to be tyrosine phosphorylated and internalised. The receptor type protein tyrosine phosphatase (PTP)kappa was constitutively associated with the cadherin-catenin complex at intact cell contacts whereas following the dissociation of adherens junctions, the internalised components of the cadherin-catenin complex were tyrosine phosphorylated and associated with the cytosolic PTP SHP-1. In isolated acini, inhibition of endogenous protein tyrosine phosphatases alone was sufficient to induce dissociation of adherens junctions analogous to that found with supramaximal caerulein stimulation. Dissociation of actin microfilaments had no effect on adherens junction integrity.

CONCLUSIONS

These data identify tyrosine phosphorylation as the key regulator for cell contacts at adherens junctions and suggest a definitive role for the protein tyrosine phosphatases PTPkappa and SHP-1 in the regulation, maintenance, and restitution of cell adhesions in a complex epithelial organ such as the pancreas.

No indications for altered essential fatty acid metabolism in two murine models for cystic fibrosis

A deficiency of essential fatty acids (EFA) is frequently described in cystic fibrosis (CF), but whether this is a primary consequence of altered EFA metabolism or a secondary phenomenon is unclear. It was suggested that defective long-chain polyunsaturated fatty acid (LCPUFA) synthesis contributes to the CF phenotype. To establish whether cystic fibrosis transmembrane conductance regulator (CFTR) dysfunction affects LCPUFA synthesis, we quantified EFA metabolism in cftr-/-CAM and cftr+/+CAM mice. Effects of intestinal phenotype, diet, age, and genetic background on EFA status were evaluated in cftr-/-CAM mice, DeltaF508/DeltaF508 mice, and littermate controls. EFA metabolism was measured by 13C stable isotope methodology in vivo. EFA status was determined by gas chromatography in tissues of cftr-/-CAM mice, DeltaF508/DeltaF508 mice, littermate controls, and C57Bl/6 wild types fed chow or liquid diet. After enteral administration of [13C]EFA, arachidonic acid (AA) and docosahexaenoic acid (DHA) were equally 13C-enriched in cftr-/-CAM and cftr+/+CAM mice, indicating similar EFA elongation/desaturation rates. LA, ALA, AA, and DHA concentrations were equal in pancreas, lung, and jejunum of chow-fed cftr-/-CAM and DeltaF508/DeltaF508 mice and controls. LCPUFA levels were also equal in liquid diet-weaned cftr-/-CAM mice and littermate controls, but consistently higher than in age- and diet-matched C57Bl/6 wild types. We conclude that cftr-/-CAM mice adequately absorb and metabolize EFA, indicating that CFTR dysfunction does not impair LCPUFA synthesis. A membrane EFA imbalance is not inextricably linked to the CF genotype. EFA status in murine CF models is strongly determined by genetic background.

Linkage of oxidative and nonoxidative ethanol metabolism in the pancreas and toxicity of nonoxidative ethanol metabolites for pancreatic acinar cells

BACKGROUND

Alcohol abuse is a major cause of pancreatic damage. Recent experimental evidence suggests that fatty acid ethyl esters (FAEE), nonoxidative ethanol metabolites, injure pancreatic acinar cells. Linkage between oxidative and nonoxidative metabolism of ethanol in the pancreas may contribute to increased FAEE levels.

METHODS

To study the association between oxidative and nonoxidative ethanol metabolism, FAEE concentration and FAEE synthase activity in rat pancreatic and liver homogenates incubated with ethanol were evaluated with and without inhibitors of oxidative ethanol metabolism. For toxicity studies, trypsinogen activation peptide synthesis as a measure of pancreatic cell injury was quantitated in unstimulated and cerulein-stimulated isolated pancreatic acinar cells incubated with ethanol or FAEE.

RESULTS

Inhibition of oxidative ethanol metabolism results in a 2- to 3-fold increase in nonoxidative ethanol metabolism to FAEE in pancreas and in liver. Both ethanol and FAEE induce increased intracellular trypsinogen activation by more than 50% in the presence of physiologic concentrations of cerulein in vitro.

CONCLUSIONS

These findings demonstrate that the inhibition of oxidative ethanol metabolism results in an increase in flux through the nonoxidative pathway and support the proposition that alcohol-induced pancreatic injury is mediated at least in part by FAEE, which are important products of pancreatic ethanol metabolism.

Activation of pancreatic acinar cells on isolation from tissue: cytokine upregulation via p38 MAP kinase

Cytokines produced by pancreatic acinar cells may mediate cell death and recruitment of inflammatory cells into pancreas in pancreatitis and other disorders. Here, we demonstrate mRNA expression for a number of cytokines in acini isolated from rat pancreas. Using RNA from microscopically selected individual cells, we confirmed the acinar cell as a source for cytokine expression. Competitive RT-PCR, Western blot analysis, and immunocytochemistry showed large amounts of monocyte chemotactic protein-1 and interleukin-6 compared with other cytokines. Cytokine expression was inhibited by either inhibitors of p38 mitogen-activated protein kinase (MAPK), SB-202190 and SB-203580, or (less strongly) by the transcription factor nuclear factor (NF)-kappaB inhibitor MG-132. A combination of SB-203580 and MG-132 inhibited mRNA expression of all cytokines by >90%. The results suggest a major role for p38 MAPK and involvement of NF-kappaB in cytokine expression in pancreatic acinar cells. In contrast to isolated acini, we detected no or very low cytokine expression in normal rat pancreas. Our results indicate that activation of p38 MAPK, transcription factors, and cytokines occurs during removal of the pancreas from the animal and isolation of acini.

Multiple isoforms of the ryanodine receptor are expressed in rat pancreatic acinar cells

Regulation of cytosolic Ca(2+) is important for a variety of cell functions. The ryanodine receptor (RyR) is a Ca(2+) channel that conducts Ca(2+) from internal pools to the cytoplasm. To demonstrate the presence of the RyR in the pancreatic acinar cell, we performed reverse transcriptase (RT)-PCR, Western blot, immunocytochemistry and microscopic Ca(2+)-release measurements on these cells. RT-PCR showed the presence of mRNA for RyR isoforms 1, 2 and 3 in both rat pancreas and dispersed pancreatic acini. Furthermore, mRNA expression for RyR isoforms 1 and 2 was demonstrated by RT-PCR in individual pancreatic acinar cells selected under the microscope. Western-blot analysis of acinar cell immunoprecipitates, using antibodies against RyR1 and RyR2, showed a high-molecular-mass (>250 kDa) protein band that was much less intense when immunoprecipitated in the presence of RyR peptide. Functionally, permeablized acinar cells stimulated with the RyR activator, palmitoyl-CoA, released Ca(2+) from both basolateral and apical regions. These data show that pancreatic acinar cells express multiple isoforms of the RyR and that there are functional receptors throughout the cell.

Actin coating of secretory granules during regulated exocytosis correlates with the release of rab3D

The present study describes a novel phenomenon in pancreatic acinar cells undergoing regulated exocytosis. When acinar cell preparations were challenged with the secretagogue carbamylcholine, a subpopulation of zymogen granules became coated with filamentous actin. These zymogen granules were always in proximity of the acinar cell apical membrane (the site of exocytosis) but did not appear to have fused yet. They were distinct from regular zymogen granules not only because of their association with filamentous actin, but also because the majority of them lacked the zymogen granule marker rab3D, a small GTPase implicated in regulated exocytosis. The apparent loss of rab3D, presumed to result from the release of rab3D from the granule membranes, could be prevented by agents that modulate the actomyosin system as well as by GTP[gammaS]. These data suggest that zymogen granules engaging in exocytosis become coated with actin before fusion and that this actin coating is tightly coupled to the release of rab3D. We propose that rab3D is involved in the regulation of actin polymerization around secretory granules and that actin coating might facilitate the movement of granules across the subapical actin network and toward their fusion site.

A membrane lipid imbalance plays a role in the phenotypic expression of cystic fibrosis in cftr(-/-) mice

A deficiency in essential fatty acid metabolism has been reported in plasma from patients with cystic fibrosis (CF). However, its etiology and role in the expression of disease is unknown. The objective of this study was to determine whether alterations in fatty acid metabolism are specific to CF-regulated organs and whether they play a role in the expression of disease. A membrane lipid imbalance was found in ileum, pancreas, and lung from cftr(-/-) mice characterized by an increase in phospholipid-bound arachidonic acid and a decrease in phospholipid-bound docosahexaenoic acid (DHA). This lipid imbalance was observed in organs pathologically affected by CF including lung, pancreas, and ileum and was not secondary to impaired intestinal absorption or hepatic biosynthesis of DHA. As proof of concept, oral administration of DHA to cftr(-/-) mice corrected this lipid imbalance and reversed the observed pathological manifestations. These results strongly suggest that certain phenotypic manifestations of CF may result from remediable alterations in phospholipid-bound arachidonic acid and DHA levels.

On the protective mechanisms of nitric oxide in acute pancreatitis

BACKGROUND

Ectopic protease activation, microcirculatory changes, and leucocyte activation are the main events in the pathogenesis of acute pancreatitis. Nitric oxide (NO) is known to be a key mediator in the normal and inflamed pancreas.

AIMS

To investigate the targets on which NO exerts its effect in caerulein induced pancreatitis.

METHODS

Acute pancreatitis was induced in rats which additionally received either the NO synthase substrate, L-arginine; the NO donor, sodium nitroprusside; or the NO synthase inhibitor, N-nitro-L-arginine methyl ester (L-NAME). At six hours, pancreatic injury (oedema, leucocyte content, ectopic trypsinogen activation) was analysed and pancreatic oxygenation and perfusion were determined. A direct influence of NO on amylase secretion and trypsinogen activation was evaluated separately in vitro.

RESULTS

Both NO donors reduced the grade of inflammation. L-NAME increased the severity of inflammation, while decreasing pancreatic tissue oxygenation. Although neither amylase secretion nor intracellular trypsinogen activation in caerulein stimulated pancreatic acini was influenced by either NO donors or inhibitors, both NO donors decreased intrapancreatic trypsinogen activation peptide (TAP) and pancreatic oedema in vivo, and L-NAME increased TAP.

CONCLUSIONS

NO protects against injury caused by pancreatitis in the intact animal but has no discernible effect on isolated acini. It is likely that in pancreatitis NO acts indirectly via microcirculatory changes, including inhibition of leucocyte activation and preservation of capillary perfusion.

Enhanced secretion of amylase from exocrine pancreas of connexin32-deficient mice

To determine whether junctional communication between pancreatic acinar cells contributes to their secretory function in vivo, we have compared wild-type mice, which express the gap junctional proteins connexin32 (Cx32) and connexin26, to mice deficient for the Cx32 gene. Pancreatic acinar cells from Cx32 (-/-) mice failed to express Cx32 as evidenced by reverse transcription-PCR and immunolabeling and showed a marked reduction (4.8- and 25-fold, respectively) in the number and size of gap junctions. Dye transfer studies showed that the extent of intercellular communication was inhibited in Cx32 (-/-) acini. However, electrical coupling was detected by dual patch clamp recording in Cx32 (-/-) acinar cell pairs. Although wild-type and Cx32 (-/-) acini were similarly stimulated to release amylase by carbamylcholine, Cx32 (-/-) acini showed a twofold increase of their basal secretion. This effect was caused by an increase in the proportion of secreting acini, as detected with a reverse hemolytic plaque assay. Blood measurements further revealed that Cx32 (-/-) mice had elevated basal levels of circulating amylase. The results, which demonstrate an inverse relationship between the extent of acinar cell coupling and basal amylase secretion in vivo, support the view that the physiological recruitment of secretory acinar cells is regulated by gap junction mediated intercellular communication.

Changes in kinesin distribution and phosphorylation occur during regulated secretion in pancreatic acinar cells

In secretory cells, microtubule- (Mt-) based motor enzymes are thought to support transport of secretory vesicles to the cell surface for subsequent release. At present, the role of Mts and kinesin in secretory vesicle transport in exocrine epithelial cells has not been defined. Furthermore, it is unclear whether an agonist-induced secretory event modifies kinesin function and distribution, thus altering vesicle transport. To this end, we utilized isolated rat pancreatic acini and cultured rat pancreatic acinar cells to examine the role of Mts and kinesin in regulated secretion. Exposure of cells to cytoskeletal antagonistic drugs demonstrated that the observed movements of apically clustered zymogen granules (ZGs) are supported by Mts, but not actin. Morphological studies of Mt organization in polarized acini show that Mt plus ends extend outward from the apical membrane toward the cell center. Immunofluorescence microscopy in both cell models revealed a clear association of kinesin with apical ZGs, while quantitative immunoblot analysis of pancreatic subcellular fractions confirmed kinesin enrichment on ZG membranes. In addition, microinjection of kinesin antibodies into cultured acinar cells inhibited ZG movements. Indirect immunofluorescence staining of isolated cells and quantitative Western blotting of isolated ZGs revealed that kinesin association with granule membranes increased up to 3-fold in response to a secretory stimulus. Autoradiographic studies of 32P-labeled acini showed up to a 6-fold increase in kinesin heavy chain (KHC) phosphorylation during stimulated secretion. These studies provide the first direct evidence that Mts and kinesin support ZG movements and that physiological agonists induce a marked phosphorylation of KHC while increasing the association of kinesin with ZG membranes. These changes during agonist stimulation suggest that the participation of kinesin in zymogen secretion is regulated.

Elevated calcium and activation of trypsinogen in rat pancreatic acini

BACKGROUND

Acute pancreatitis associated with hypercalcaemia has been described in humans and experimental animals. It has been demonstrated that calcium dose dependently accelerates trypsinogen activation, and it is generally believed that ectopic activation of digestive enzymes is an early event in the pathophysiology of acute pancreatitis.

AIMS AND METHODS

Trypsinogen activation peptide (TAP) was measured in isolated rat pancreatic acini exposed to elevated extracellular calcium in order to investigate the association between calcium and trypsinogen activation in living cells. TAP was determined in the culture medium either before (extracellular compartment) or after (intracellular compartment) cell homogenisation.

RESULTS

Neither secretory stimulation nor elevated calcium alone caused an increase in TAP levels. Maximal cerulein or carbachol stimulation superimposed on high medium calcium, however, significantly increased intracellular trypsinogen activation twofold. This increase was inhibited by either NG-monomethyl-L-arginine (L-NMMA) or verapamil. Acinar cell morphology and function remained intact as demonstrated by electron microscopy and secretagogue dose-response studies.

CONCLUSIONS

These results support the hypothesis that increased intracellular trypsinogen activation is an early step in the pathogenesis of hypercalcaemia induced pancreatitis. The model may have a bearing on other types of pancreatitis as elevated cytosolic calcium is thought to be an early event in the pathogenesis of acute pancreatitis in general.

Pancreatic exocrine secretion is blocked by inhibitors of methylation

A number of early experiments suggested a relationship between methyl group metabolism and the exocrine secretion of the pancreas. These included nutritional studies showing that ethionine, the ethyl analog of methionine which inhibits cellular methylation reactions, is a specific pancreatic toxin. Other studies indicated that protein carboxymethylation might be involved. We now show that in vivo ethionine inhibits amylase secretion from freshly isolated rat pancreatic acini, while in vitro ethionine inhibits amylase secretion from the AR42J pancreatic cell line. S-Adenosylhomocysteine (SAH) is a product inhibitor of all methyltransferase reactions involving S-adenosylmethionine (SAM), and treatments that elevate cellular levels of SAH such as inhibition of S-adenosylhomocysteine hydrolase and the in vitro addition of adenosine and homocysteine result in the inhibition of amylase secretion in both isolated pancreatic acini and AR42J cells. Measurement of SAM and SAH levels in AR42J cells shows that inhibition of secretion is more closely related to elevation of SAH levels than to a decrease in the SAM/SAH ratio. Small G-proteins are carboxymethylated on the C-terminal prenylated cysteine and inhibitors of membrane-associated prenylcysteine methyltransferase, N-acetylfarnesylcysteine, N-acetylgeranylgeranylcysteine, and farnesylthioacetic acid (FTA), block secretion in AR42J cells. N-Acetylgeranylcysteine is not an inhibitor of the methyltransferase and does not inhibit amylase secretion. FTA inhibits membrane-associated prenylcysteine methyltransferase from AR42J cells with a Ki in the 45-69 microm range. These results suggest that a methylation event is needed for pancreatic exocrine secretion which may be the reversible methylation of a G-protein involved in signal transduction or membrane trafficking.

The action of the cholecystokinin-A receptor antagonist, devazepide, on the digestive system of the chicken

The influence of the cholecystokinin (CCK)-A receptor antagonist, devazepide (DVZ), on the chicken digestive tract was investigated. The passage of food from the crops of birds treated with DVZ was not significantly different from that of the control. DVZ treatment did not inhibit the biliary flow stimulated by the CCK analogue, caerulein. Dispersed chicken pancreatic acini stimulated with CCK were treated with various concentrations of DVZ. At 10-5 M, DVZ completely inhibited amylase release; this concentration was much higher than those reported to have similar effects in mammals. The results suggest that the action DVZ as a CCK antagonist in the chicken is very weak.

Nitric oxide modulates pancreatic basal secretion and response to cerulein in the rat: effects in acute pancreatitis

BACKGROUND/AIMS

Nitric oxide synthase activity is detected in the pancreas, but the role of NO on pancreatic function has not been fully characterized. The aim of this study was to evaluate the role of NO in normal and diseased pancreatic function.

METHODS

Amylase and NO secretion were measured in vivo in rats and in vitro in dispersed acini, with and without NO synthesis blockade, by NG-nitro-L-arginine methyl ester (L-NAME). Rats were subjected to cerulein-induced pancreatitis, and the effects of L-NAME or NO donors were assessed.

RESULTS

L-NAME reduced amylase output to 60% of basal. This effect was reversed by L-arginine. The secretory response to optimal doses of cerulein induced a poor amylase secretion and a marked release of NO. High doses of cerulein in combination with L-NAME inhibited NO formation and amylase secretion. In dispersed acini, supramaximal cerulein concentrations induced NO release, but the amylase dose-response curve was not modified by NO inhibition. In acute pancreatitis, L-NAME increased amylasemia and tissue myeloperoxidase activities, whereas NO donors reduced amylasemia, lipasemia, and the histological damage score.

CONCLUSIONS

The L-arginine/NO pathway facilitates basal and stimulated pancreatic secretion in vivo. NO donor drugs may improve the course of acute pancreatitis.

Cholecystokinin is not a major regulator in the digestive system in the chicken

To find out whether physiological concentrations of cholecystokinin (CCK), a gastrointestinal hormone in mammals, are also active in chickens, the pancreatic amylase secretory response to CCK-8 was investigated in vitro. Rat pancreatic acini responded to the physiological concentration of CCK-8, but in chickens amylase release was induced at a concentration of CCK-8 1000 times higher than that observed in rats. In another experiment, biliary flow was tested with several doses of CCK-8. The bile flow was stimulated in a dose-dependent fashion, but a significant enhancement was not obtained at a concentration of 0.5 micrograms CCK-8/kg body weight, which was considerably higher than physiological ones. It is concluded that endogenous CCK does not have an important role in the digestive system in the chicken.

Transport and interaction of nitrogen oxides and NO2 with CO2-HCO3- transporters in pancreatic acini

Recently, we showed that NO2- increases gap junction (GJ) permeability and synchronizes intracellular Ca2+ concentration oscillations in pancreatic acini (Loessburg et al., J. Biol. Chem. 268: 19769-19775, 1993). NO2- is also an end product of nitric oxide (NO) production and metabolism. Because of the effect of NO2- on GJ permeability and the possible importance of NO2- in NO metabolism and cytotoxicity, we used pancreatic acinar cells and intracellular pH (pHi) measurements to study the interaction of nitrogen oxides and NO2- with cellular proteins. Exposing cells to NO2- resulted in a concentration-dependent cytosolic acidification. The acidification did not require the transport of NO2- and was not mediated by diffusion of HNO2. Because the acidification was prevented by CO2-HCO3- and inhibition of carbonic anhydrase, it is possible that other nitrogen oxides present in a solution containing NO2- enter the cells by diffusion and interact with OH- or H2O to stably acidify the cytosol. NO2- itself is shown to be transported by the HCO3- transporters present in the plasma membrane. Thus manipulation of the cellular Cl- gradient and 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS) were used to show Cl-/NO2- exchange, whereas stimulation of external Na(+)-dependent amiloride-insensitive and DIDS-sensitive pHi increase in acidified cells was used to demonstrate a Na(+)-(NO2-)n cotransport. Hence NO2- can be a convenient substitute for HCO3- when studying HCO3- transport in an open system. The studies also show that cellular levels of nitrogen oxides and NO2- can be modulated by the cellular HCO3(-)-buffering system.(ABSTRACT TRUNCATED AT 250 WORDS)

Heterogeneity and contact-dependent regulation of amylase release by individual acinar cells

We have used a reverse hemolytic plaque assay to investigate the amylase release of single and aggregated pancreatic acinar cells. We have found that a minority of single acinar cells released detectable amounts of amylase under basal conditions and were modestly stimulated, in a dose-dependent manner, during a 30-min exposure to concentrations of carbamylcholine (CCh) ranging from 10(-8) to 10(-5) M. This stimulation was largely accounted for by the recruitment of additional secreting cells, rather than by a significant increase in their individual secretory output. We have also observed that aggregates comprising two to five acinar cells secreted more frequently and released more amylase than single acinar cells in the presence of each of the CCh concentrations tested. Under both basal conditions and following CCh stimulation, the proportion of secreting aggregates and their amylase output increased linearly with the aggregate size. Under basal conditions as well as in the presence of secretagogue concentrations in the 10(-8) - 10(-7) M range, individual cells contributed similarly to amylase secretion whether they were single or part of aggregates. By contrast, following stimulation by 10(-6) - 10(-5) M CCh, aggregated cells showed a much higher average secretion than single cells. Investigating the mechanism of this contact-dependent effect, we found that 10(-3) M heptanol did not significantly modify the secretion of single cells and markedly promoted the basal amylase release of acinar cell pairs. This effect was associated with a marked reduction in gap junctional communication between acinar cells, as evaluated by microinjection of Lucifer yellow, and was not observed during exposure to high concentrations of CCh, which also reduced junctional communication. These data show that pancreatic acinar cells are intrinsically heterogeneous in their ability to release amylase and that their basal as well as stimulated secretion are promoted by the establishment of direct intercellular contacts. Our experiments also suggest that junctional coupling contributes to the contact-dependent mechanism which enhances the recruitment of secreting cells and their individual output. These observations strengthen the view that direct interactions between acinar cells are essential in the control of pancreatic secretion.

Endogenous cholecystokinin is not a major regulator of food intake in the chicken

This study investigated whether or not endogenous cholecystokinin exerts satiety effects in chickens. After several doses (0, 1, 2 and 4 micrograms.kg body weight-1) of intravenous injection of caerulein, the bile flow was increased in a dose-dependent fashion. However, the pharmacological level of caerulein failed to suppress the food intake of chickens. Two potent stimulators of endogenous cholecystokinin, i.e., soybean trypsin inhibitor and phenylalanine were administered to chickens before feeding and food intake was determined over 2 h. The soybean trypsin inhibitor and phenylalanine did not alter food intake. Devazepide, a cholecystokinin-A receptor antagonist, significantly decreased amylase release from the dispersed chicken pancreatic acini stimulated by caerulein. However, devazepide did not improve food intake of the chicken. The results obtained suggest that endogenous cholecystokinin may not act as a satiety signal in chickens.

Characterization of cAMP-dependent protein kinase activation by CCK in rat pancreas

This study reports on the use of a new sensitive assay of cAMP-dependent protein kinase activity to examine the effect of cholecystokinin (CCK) on the cAMP second messenger cascade in rat pancreatic acini. Treatment of acini with both low (pM) and high (nM) concentrations of CCK was associated with an increase in cAMP-dependent protein kinase activity. The increases in kinase activity were detected in the absence of phosphodiesterase inhibition, a condition required to detect a measurable increase in cellular cAMP in these cells. Furthermore, the cAMP cascade was dissociated from the secretory effects of CCK, since the CCK analogue, OPE, mediates enzyme secretion but does not increase cellular cAMP levels or kinase activity.

Protein kinase A modulates Ca(2+)- and protein kinase C-dependent amylase release in permeabilized rat pancreatic acini

The role of protein kinase A (PKA) in the release of amylase from permeabilized pancreatic acini was investigated. Addition of cyclic AMP (cAMP) to permeabilized acini resulted in a potentiation of Ca(2+)-dependent amylase release, shifting the Ca2+ dose/response curve leftwards. As with protein kinase C (PKC) activation, this is due to an increase in the time of active discharge. The effect of cAMP was shown to be blocked by two inhibitors of PKA, H89 and the PKI-(5-24)-peptide. At low concentration, cAMP synergizes from phorbol 12-myristate 13-acetate (PMA), while at optimal concentrations cAMP and PMA are additive. PKA and PKC appear to work via similar, but not identical mechanisms.

Activation of protein kinase C is not an absolute requirement for amylase release from permeabilized rat pancreatic acini

The effect of protein kinase C (PKC) on amylase discharge from streptolysin-O-permeabilized rat pancreatic acini was investigated. Addition of phorbol 12-myristate 13-acetate (PMA) to permeabilized cells potentiated Ca(2+)-stimulated release, but had no effect on discharge at non-stimulatory Ca2+ concentrations. PMA markedly shifted the Ca(2+)-concentration-dependence of amylase discharge to the left, by enhancing the time over which the permeabilized cells release. This effect was inhibited by both staurosporine and PKC-19-31-amide peptide inhibitor, indicating that the effect of PMA was due to its action on PKC. Staurosporine also partially inhibited amylase release at the optimal concentration of Ca2+; this effect was not replicated by the more specific PKC-19-31-amide peptide inhibitor and may be due to an effect on another second-messenger system. PKC appears to be an important modulator of release in pancreatic acini, but its activation is not an absolute requirement for Ca(2+)-dependent amylase discharge.

A synthetic peptide of the rab3a effector domain stimulates amylase release from permeabilized pancreatic acini

In this study we have employed a synthetic peptide of the rab3a effector domain, rab3AL, to examine whether a rab-like low molecular weight GTP-binding protein is involved in protein release from the rat pancreatic acinar cell. The peptide was found to be a potent stimulator of amylase release from streptolysin-O-permeabilized pancreatic acini, with an EC50 of approximately 60 microM. Stimulation of amylase discharge by rab3AL did not occur using either intact acini or permeabilized acini depleted of ATP. In contrast, a different effector domain peptide of the rab2 protein, rab2AL, a peptide with distinct sequence homology to rab3AL, was unable to stimulate amylase release, suggesting the specificity of the rab3AL response to rab3-like proteins. rab3AL stimulated release at [Ca2+] that were nonstimulatory in the absence of the peptide (10 nM). rab3AL potentiated the effect of guanosine 5'-[gamma-thio]triphosphate on amylase secretion and decreased the amount of guanosine 5'-[gamma-thio]triphosphate required for maximal secretion, suggesting that these two agents interact to modulate a distal step(s) of secretion. The above results provide functional evidence for the role of a rab-like low molecular weight GTP-binding protein and its effector protein(s) in the control of protein release from pancreatic acini. Because the discharge response to rab3AL is near the maximal obtainable from permeabilized acini, our results would suggest that rab3-like proteins control an important step in regulated secretion of amylase.

Determination of plasma cholecystokinin (CCK) concentrations by bioassay and radioimmunoassay in man. A critical evaluation

The present investigation was designed to perform a direct comparison of a rat pancreatic acini bioassay system and a specific CCK radioimmunoassay (antiserum G-160) for the measurement of fasting and meal-stimulated plasma CCK in the presence and absence of the CCK receptor antagonist loxiglumide. The G-160 CCK antiserum is directed against the C-terminal O-sulfated tyrosine residue of the CCK molecule which is essential for full bioactivity of CCK peptides. For plasma extraction prior to bioassay measurement, hydrophobic reverse-phase chromatography on octadecylsilane cartridges was employed and resulted in simultaneous adsorption and elution of both CCK peptides and loxiglumide with recoveries of 87.5 +/- 9% and 75.0 +/- 5.9%, respectively. In the absence of loxiglumide, fasting and meal-stimulated values for CCK-like bioactivity and CCK-immunoreactivity (IR-CCK) were nearly identical (basal values: 1-2 pmol/l; meal-stimulated plateau levels: 4-6 pmol/l). After intravenous infusion of loxiglumide (30 mg/kg/h for 10 min, 10 mg/kg/h thereafter), resulting in plasma steady state levels of 200-300 mumol/l, meal-stimulated CCK-like bioactivity was undetectable, whereas IR-CCK levels were augmented 6.5-fold. In the bioassay system, standard samples containing 50 mumol/l loxiglumide produced complete inhibition of acinar lipase release in response to 50 pmol/l synthetic CCK-8. We conclude, that postprandial circulating non-CCK-like factors do not contribute significantly to the direct receptor-mediated stimulation of exocrine pancreatic secretion. The good agreement of CCK-like bioactivity and IR-CCK levels in the absence of loxiglumide confirms the sensitive and specific recognition of bioactive CCK peptides by the G-160 antiserum and suggests that this antibody exerts binding characteristics probably similar to a pancreatic acinar receptor.

Agonist-sensitive and -insensitive intracellular Ca2+ pools. Separate Ca(2+)-releasing mechanisms revealed by manoalide and benzohydroquinone

The mechanism of action of a novel compound, 2,5-di-(t-butyl)-1,4-benzohydroquinone (BHQ), used to modulate cell free cytosolic Ca2+ concentration ([Ca2+]i) was studied in AR42J cells and pancreatic acini by using single-cell fluorescence techniques applied to Fura-2-loaded cells. In the presence of extracellular Ca2+ (Ca(2+)out), BHQ induced a biphasic [Ca2+]i increase, an initial and rapid transient followed by a sustained increase. The initial increase was due to Ca2+ release from intracellular stores, being independent of Ca(2+)out. The sustained response was due to Ca2+ entry, being dependent on Ca(2+)out, blocked by La3+ and correlated with an increased rate of Mn2+ entry, all indicative of increased plasma-membrane permeability to Ca2+. Treatment of AR42J cells with BHQ for about 5 min reversibly blocked agonist-dependent Ca2+ release and oscillations, whereas agonist pretreatment decreased, but did not prevent, the effects of BHQ on [Ca2+]i. Accordingly, depletion of the Ins(1,4,5)P3-mobilizable pool in permeabilized AR42J cells by BHQ required 5 min of incubation, although inhibition of the internal Ca2+ pump by BHQ was rapid. These observations suggest that BHQ mobilized an additional intracellular Ca2+ pool that did not respond to changes in Ins(1,4,5)P3. Manoalide, an inhibitor of Ca2+ channels, inhibited agonist-evoked [Ca2+]i oscillation and [Ca2+]i increase in a dose- and time-dependent manner without significant effect on internal Ca2+ pumps and Ca2+ content of the internal stores. Manoalide also inhibited the BHQ-evoked [Ca2+]i increase in the absence and presence of Ca(2+)out. Neither BHQ nor manoalide affected Ins(1,4,5)P3 levels in resting or stimulated cells. Therefore, the effect of BHQ appears to involve unmasking of passive Ca(2+)-permeation pathways in the plasma and intracellular membranes that do not respond to cholecystokinin octapeptide, following its described inhibition of the internal-store Ca2+ pumps responsible for accumulating Ca2+ in these pools.

Mammalian Sec23p homologue is restricted to the endoplasmic reticulum transitional cytoplasm

The yeast Sec23 protein is required in vivo and in vitro for transport of proteins from the endoplasmic reticulum (ER) to the Golgi apparatus. Ultrastructural localization of the Sec23p mammalian homologue (detected by antibody cross-reaction) in exocrine and endocrine pancreatic cells shows a specific distribution to the cytoplasmic zone between the transitional ER cisternae and Golgi apparatus where it appears associated with the tubular protuberances of the transitional ER cisternae, as well as with a population of vesicles, and surrounding cytoplasm. When ER-Golgi transport is interrupted with an energy poison, protuberances and transfer vesicles markedly decrease but Sec23p immunoreactive sites remain in the transitional cytoplasm not apparently tethered by membrane attachment. This unanticipated degree of organization suggests that cytosolic proteins, such as Sec23p, may be retained in specialized areas of the cytoplasm. A structure within the transitional zone may organize the flux of transport vesicles and Sec proteins so as to ensure efficient protein traffic in this limb of the secretory pathway.

Effect of protein kinase C on amylase secretion and cyclic AMP production in rat pancreatic acinar cells

The authors examined the effects of protein kinase C on secretin-induced amylase release and cyclic AMP production in rat pancreatic acinar cells. Secretin (10(-6) M) and 12-O-tetradecanoyl-phorbol 13-acetate (TPA) (10(-6) M) induced 53% and 60% increase of amylase release from the basal level, respectively during 10 min. Simultaneous addition of TPA and secretin resulted in 42% amylase release from the basal level for 10 min. Suppression of secretin-induced amylase release was evident within 5 min of pretreatment with TPA. TPA showed the same effect on cyclic AMP production; secretin-induced increase of cyclic AMP was suppressed by pretreatment of TPA for 5 min. To explore the mechanism by which TPA inhibits secretin-induced cyclic AMP production, we also examined the effects of protein kinase C purified from rat brain on adenylate cyclase activity in pancreatic acinar membranes. Basal, forskolin- and secretin plus guanosine 5'-[gamma-thio]trisphosphate-stimulated adenylate cyclase activity were inhibited by protein kinase C in the presence of Ca++. These results suggest that protein kinase C might have a role in the inhibitory effect on adenylate cyclase in exocrine pancreas.

Ca2(+)-dependent amylase secretion from pancreatic acinar cells occurs without activation of phospholipase C linked G-proteins

We have examined the influence of guanine nucleotides on Ca2(+)-dependent amylase secretion from SLO permeabilized rat pancreatic acini. GTP gamma S (100 microM) stimulated Ca2+ dependent amylase release, decreasing the EC50 for Ca2+ from 1.4 to 0.8 microM. By contrast, GDP (1mM) and dGDP (1mM) inhibited the maximal Ca2(+)-dependent secretory response. Measurement of IP3 liberation showed that Ca2+ stimulation did not increase the activity of phospholipase C (PLC) postulated to be linked to a G-protein termed Gp; GDP and dGDP must therefore be exerting their inhibitory action via a GTP-binding protein distinct from the PLC-linked Gp.

Intracellular activation of digestive zymogens in rat pancreatic acini. Stimulation by high doses of cholecystokinin

The mechanism by which digestive zymogens become activated during acute pancreatitis remains poorly understood. Given the ability for cholecystokinin (CCK) to induce pancreatitis in vivo, the effects of high dose CCK on preparations of isolated pancreatic acini were examined. Using an immunologic technique for the detection of zymogen activation, CCK was found to stimulate the conversion of procarboxypeptidase A1 to a 35-kD form having the same net charge and electrophoretic mobility as purified recombinant carboxypeptidase A1. This enhanced conversion was proportional to the dose of CCK (maximal at 100 nM), and time dependent. CCK also produced changes in the electrophoretic mobility of procarboxypeptidase B and chymotrypsinogen 2 immunoreactivity, consistent with activation of these zymogens. These events were detectable only within acinar cell pellets and not in the incubation medium, suggesting an intracellular site of conversion. The conversion of procarboxypeptidase A1 to its active form was inhibited by pretreatment with the weak base chloroquine (40 microM) and the protonophore monensin (10 microM). This conversion was also inhibited by pretreatment with the serine protease inhibitor benzamidine (10 mM) but not the cysteine protease inhibitor E64 (100 microM). The results suggest that high dose CCK stimulates the intracellular activation of digestive zymogens within isolated pancreatic acini. This event appears to require an acidic subcellular compartment and serine protease activity.

Uric acid synthesis by avian exocrine pancreas

1. Chicken pancreas has been shown to synthesize and secrete uric acid. Uric acid synthesis from xanthine in vitro by isolated pancreatic acinii is saturable and dependent on the activity of xanthine dehydrogenase. 2. Chicken pancreas is unable to synthesize uric acid de novo but the variety of substrates which support urate synthesis suggests that it occurs by the purine degradation pathway.

Measurement of tissue cholecystokinin (CCK) concentrations by bioassay and specific radioimmunoassay: characterization of the bioactivity of CCK-58 before and after tryptic cleavage

Cholecystokinin (CCK) was measured in an extract of porcine brain by a bioassay system based on the enzyme release from isolated pancreatic acini and a specific radioimmunoassay. The tissue extract represented a crude peptide preparation of porcine brain that contained several molecular forms of CCK, most of them of high molecular weight including CCK-58. The different molecular forms of CCK in the porcine brain extract were isolated by high performance liquid chromatography (HPLC). Determination of CCK-like bioactivity and immunoreactivity after HPLC was performed in parallel by bioassay and radioimmunoassay, respectively CCK-58 was the most abundant molecular form in the porcine brain extract, followed by CCK-33, and CCK-8. Both assay systems measured similar relative concentrations of all different molecular forms of CCK. To elucidate the biological potency of CCK-58 before and after tryptic cleavage, a CCK-58-enriched fraction was prepared by HPLC. Part of this material was quantitatively cleaved by trypsin resulting in the formation of small molecular forms of CCK. Bioactivity and immunoreactivity of equal amounts of cleaved and uncleaved material (= CCK-58) were determined by bioassay and radioimmunoassay in parallel. Cleavage of CCK-58 increased CCK-like bioactivity by 260% and CCK-like immunoreactivity by 310%. These results indicate that in a rat pancreatic acini system, porcine CCK-58 exerts 25-30% bioactivity compared to smaller CCK forms. The specific CCK antiserum G-160 seems to possess 25-30% affinity to CCK-58 in comparison to trypsin-cleaved CCK-58. It can be concluded that this antiserum exhibits an affinity to different molecular forms of CCK which parallels their relative bioactivity.(ABSTRACT TRUNCATED AT 250 WORDS)

Relationship between hormonal, GTP and Ins(1,4,5)P3-stimulated Ca2+ uptake and release in pancreatic acinar cells

Electrically permeabilized rat pancreatic acini were used to evaluate the contributions of GTP and Ins(1,4,5) P3 to hormone-stimulated Ca2+ uptake and release from intracellular pools. Treatment of permeabilized acini with Ca2+-mobilizing hormones, GTP or GTP[S] resulted in stimulation of an ATP-dependent, VO4(2-)-sensitive Ca2+ uptake into a non-mitochondrial intracellular pool. GTP and GTP[S] also augmented the hormone-mediated stimulation of Ca2+ uptake. Including oxalate in the uptake medium increased Ca2+ uptake into this pool but did not modify the stimulation of Ca2+ uptake induced by hormones or GTP. Ins(1,4,5)P3 released all the extra Ca2+ accumulated as a result of hormone, GTP or GTP[S] stimulation. Hence, these stimuli activated the Ca2+ pump localized in the membrane of the hormone and Ins(1,4,5)P3-sensitive Ca2+ pool. Including 2,3-diphosphoglyceric acid (PGA) [an inhibitor of Ins(1,4,5)P3 hydrolysis] in the incubation medium blunted the GTP and GTP[S]-stimulated Ca2+ uptake. In the presence of PGA, the hormones inhibited Ca2+ accumulation, and GTP and GTP[S] augmented this effect. Accordingly, PGA stabilized the Ins(1,4,5)P3-evoked Ca2+ release from intracellular pools. Only in the presence of PGA was it possible to demonstrate hormonally-evoked Ca2+ release from permeabilized cells. GTP, and more importantly GTP[S], augmented the hormone-evoked Ca2+ release. Hormones and Ins(1,4,5)P3 in the presence or absence of GTP or GTP[S] released Ca2+ from the same intracellular pool. The extent of Ca2+ release caused by the combination of hormones and GTP or GTP[S] was similar to that evoked by Ins(1,4,5)P3 alone. Taken together, these results suggest that GTP or GTP[S] facilitates stimulation of phospholipase C by hormones. Such stimulation results in stimulation of protein kinase C and increased levels of Ins(1,4,5)P3 and is sufficient to explain the effects of GTP and GTP[S] on Ca2+ uptake and release from pancreatic acinar cells.