Ryanodine receptors contribute to bile acid-induced pathological calcium signaling and pancreatitis in mice

Abstract

Biliary pancreatitis is the most common etiology for acute pancreatitis, yet its pathophysiological mechanism remains unclear. Ca2+ signals generated within the pancreatic acinar cell initiate the early phase of pancreatitis, and bile acids can elicit anomalous acinar cell intracellular Ca2+ release. We previously demonstrated that Ca2+ released via the intracellular Ca2+ channel, the ryanodine receptor (RyR), contributes to the aberrant Ca2+ signal. In this study, we examined whether RyR inhibition protects against pathological Ca2+ signals, acinar cell injury, and pancreatitis from bile acid exposure. The bile acid tauro-lithocholic acid-3-sulfate (TLCS) induced intracellular Ca2+ oscillations at 50 μM and a peak-plateau signal at 500 μM, and only the latter induced acinar cell injury, as determined by lactate dehydrogenase (LDH) leakage. Pretreatment with the RyR inhibitors dantrolene or ryanodine converted the peak-plateau signal to a mostly oscillatory pattern ( P < 0.05). They also reduced acinar cell LDH leakage, basolateral blebbing, and propidium iodide uptake ( P < 0.05). In vivo, a single dose of dantrolene (5 mg/kg), given either 1 h before or 2 h after intraductal TLCS infusion, reduced the severity of pancreatitis down to the level of the control ( P < 0.05). These results suggest that the severity of biliary pancreatitis may be ameliorated by the clinical use of RyR inhibitors.

Bile Acids Induce Pancreatic Acinar Cell Injury and Pancreatitis by Activating Calcineurin

“…Our findings that blockade of intracellular Ca 2ϩ reduced calcineurin activation are in general agreement with previous reports that sustained Ca 2ϩ signals are required to activate calcineurin (22,23 (12,25,46), Ca 2ϩ store depletion, and the subsequent opening of store operated Ca 2ϩ entry (SOCE) channels (47)(48)(49).…”

“…However, the most immediate effect of bile acids is their ability to elicit acinar cell cytosolic Ca 2ϩ signals. The signals are observed at bile acid concentrations below the critical micellar concentration (12,17) and occur even in the absence of external Ca 2ϩ (18), albeit with lower amplitude. Thus, bile acids appear to transduce the Ca 2ϩ signals not by permeabilizing the plasma membrane but by causing the opening of Ca 2ϩ channels.…”

“…Administration of submillimolar concentrations of chenodeoxycholic acid (CDC) 3 to the lumen of ex vivo ducts elicits reactive mechanisms within the pancreatic duct cell to stimulate bicarbonate secretion (10,11). However, higher concentrations of CDC induce acinar cell pathology, leading to pancreatitis (12,13).…”

Bile acids activate ryanodine receptors in pancreatic acinar cells via a direct allosteric mechanism

“…release and prolonged elevation of the intracellular Ca 2+ concentration ([Ca 2+ ]i) in the acinar cell [4]. Impaired Ca 2+ signaling is considered to be the critical molecular step of acute pancreatitis because it causes premature intraacinar protease activation and acinar cell damage that provokes the inflammation [5,6].…”

“…The mechanism underlying global Ca 2+ signals is Ca 2+ wave propagation, which involves the Ca 2+ dependent activation of ryanodine receptor (RyR) Ca 2+ release channels that show higher density in the basolateral-supranuclear region of the acinar cell. Since the ryanodine sensitive compartment is the major source of Ca 2+ under pathological Ca 2+ release, the role of RyR in the pathomechanism seems to be essential [4,10,11]. For instance, recent studies showed that Ca 2+ signals in the basolateral areas induced by supramaximal concentrations of carbachol and that of the subcellular distribution of RyR overlapped with the regions where caerulein-induced early zymogen activation occurred [10].…”