Endoplasmic reticulum Ca(2+)-ATPase inhibitors stimulate membrane guanylate cyclase in pancreatic acinar cells.

In this study, we show that particulate guanylate cyclase (GC) is present in rat pancreatic acinar cells and is located both on plasma membrane and membranes of endoplasmic reticulum (ER). Western blot analysis indicates that the enzyme isoform GC-A is present in the acinar cell membranes. The specific inhibitors of ER Ca(2+)-ATPase thapsigargin, 2,5-di-(t-butyl)-1,4-hydroquinone (BHQ), and cyclopiazonic acid all activated particulate GC in pancreatic acini, both in membrane fractions and intact cells. These inhibitors also induced dephosphorylation of GC. Dose dependencies of Ca(2+)-ATPase inhibition and GC activation by BHQ are very similar, and those for thapsigargin partially overlap. ER Ca(2+)-ATPase and GC are coimmunoprecipitated both by antisera against membrane GC and by antisera against ER Ca(2+)-ATPase, suggesting a physical association between the two enzymes. The results suggest that thapsigargin and the other inhibitors act through ER Ca(2+)-ATPase to activate membrane GC in pancreatic acinar cells, although their direct effect on GC cannot be excluded.

Pancreatic acinar cells produce, release, and respond to tumor necrosis factor-alpha. Role in regulating cell death and pancreatitis.

The aim of this study was to determine whether tumor necrosis factor-alpha (TNFalpha) and receptors for TNFalpha are expressed in the exocrine pancreas, and whether pancreatic acinar cells release and respond to TNFalpha. Reverse transcription PCR, immunoprecipitation, and Western blot analysis demonstrated the presence of TNFalpha and 55- and 75-kD TNFalpha receptors in pancreas from control rats, rats with experimental pancreatitis induced by supramaximal doses of cerulein, and in isolated pancreatic acini. Immunohistochemistry showed TNFalpha presence in pancreatic acinar cells. ELISA and bioassay measurements of TNFalpha indicated its release from pancreatic acinar cells during incubation in primary culture. Acinar cells responded to TNFalpha. TNFalpha potentiated NF-kappaB translocation into the nucleus and stimulated apoptosis in isolated acini while not affecting LDH release. In vivo studies demonstrated that neutralization of TNFalpha with an antibody produced a mild improvement in the parameters of cerulein-induced pancreatitis. However, TNFalpha neutralization greatly inhibited apoptosis in a modification of the cerulein model of pancreatitis which is associated with a high percentage of apoptotic cell death. The results indicate that pancreatic acinar cells produce, release, and respond to TNFalpha. This cytokine regulates apoptosis in both isolated pancreatic acini and experimental pancreatitis.

The role of neutrophils and platelet-activating factor in mediating experimental pancreatitis.

BACKGROUND & AIMS: Pancreatitis is characterized by inflammation and death of acinar cells. Death can occur by either necrosis or apoptosis. The initial injury may cause expression of cytokines that mediate activation and infiltration of neutrophils. The aim of this study was to assess the effect of neutrophils and platelet-activating factor (PAF) in cell death responses. METHODS: The effects of neutrophil depletion with antineutrophil serum (ANS) and a PAF antagonist (BN52021) were measured in the cerulein model of pancreatitis. Rats received a 6-hour intravenous infusion of cerulein either alone or after treatment with ANS, BN52021, or both. RESULTS: Cerulein-induced pancreatitis was characterized by neutrophilic infiltration, vacuolization of acinar cells, and foci of necrosis. Treatment with ANS and BN52021 prevented the inflammatory response caused by cerulein and decreased the cell damage. Treatment with ANS increased apoptosis in cerulein-infused animals. When BN52021 was added, apoptosis was abolished. The measurement of PAF in pancreatic tissue showed a ninefold increase with cerulein treatment alone and a 14-fold increase in cerulein-infused, neutrophil-depleted animals. CONCLUSIONS: The results indicate that cerulein stimulates pancreatic production of PAF. PAF mediates both apoptosis and neutrophil chemotaxis in the pancreas. Neutrophils in turn may convert acinar cells undergoing apoptosis into necrotic cells.