The ryanodine receptor mediates early zymogen activation in pancreatitis

Abstract

Acute pancreatitis is characterized by the pathologic activation of zymogens within pancreatic acinar cells. The process requires a rise in cytosolic Ca 2؉ from undefined intracellular stores. We hypothesized that zymogen activation is mediated by ryanodine receptor (RYR)-regulated Ca 2؉ release, because early zymogen activation takes place in a supranuclear compartment that overlaps in distribution with the RYR. Ca 2؉ signals in the basolateral, but not apical, region of acinar cells observed during supraphysiologic agonist stimulation were dependent on RYR Ca 2؉ release. Inhibition of RYR or depletion of RYR-sensitive Ca 2؉ pools each reduced pathologic zymogen activation in isolated acinar cells, but neither treatment affected amylase secretion. Inhibition of RYR also inhibited zymogen activation in vivo. We propose that Ca 2؉ release from the RYR mediates zymogen activation but not enzyme secretion. The findings imply a role for the RYR in acute pancreatitis.pancreatic acinar cell ͉ dantrolene ͉ calcium signaling

Ethanol Enhances Carbachol-induced Protease Activation and Accelerates Ca2+ Waves in Isolated Rat Pancreatic Acini

“…Acini were then stimulated with the acetylcholine analog carbachol for 60 min at 37°C. Protease activity assays were performed at room temperature using fluorogenic substrates as described previously (8). Briefly, 50 l of 400 M enzyme substrate were added to each homogenized sample, and accumulation of fluorescence was measured over 10 min using a fluorescent plate reader (Infinite M200, Tecan) at 380-nm excitation and 440-nm emission wavelengths.…”

“…We know that intracellular Ca 2ϩ release is responsible for the onset of this aberrant Ca 2ϩ signal (10). In addition, we have previously shown that the ryanodine receptor (RYR), 4 a major intracellular Ca 2ϩ channel, is localized to the basolateral region of the acinar cell and, more importantly, is linked to the onset of pathologic protease activation (8).…”

“…Following secretagogueinduced stimulation of acinar cells, the initial rise in Ca 2ϩ is predominantly controlled by two types of endoplasmic reticulum Ca 2ϩ channels: 1) the inositol 1,4,5-trisphosphate receptor (IP3R) channel, which is activated by inositol 1,4,5-trisphosphate (IP3); and 2) the RYR, which is structurally similar to the IP3R but responds to different ligands (13). We and others have shown that the RYR is excluded from the apical region but localized to the basal region, importantly, where pancreatic zymogens, particularly proteases, are first activated during acute pancreatitis (8,14 We have linked RYR Ca 2ϩ release in the basal region of the acinar cell to pathologic, premature intra-acinar protease activation, a critical and primary event in the pathogenesis of pancreatitis (15 (9,16,17). In the current study, we examined the role of ethanol in modulating the RYR Ca 2ϩ signal and its effect on mediating protease activation.…”

“…Several lines of evidence also link ethanol to aberrant Ca 2ϩ 3 signaling (6). High amplitude, aberrant, intracellular Ca 2ϩ waves that propagate from the apical to basolateral region of the acinar cell predispose to early features of pancreatitis, particularly intra-acinar protease activation (8,9). We know that intracellular Ca 2ϩ release is responsible for the onset of this aberrant Ca 2ϩ signal (10).…”

“…Following secretagogueinduced stimulation of acinar cells, the initial rise in Ca 2ϩ is predominantly controlled by two types of endoplasmic reticulum Ca 2ϩ channels: 1) the inositol 1,4,5-trisphosphate receptor (IP3R) channel, which is activated by inositol 1,4,5-trisphosphate (IP3); and 2) the RYR, which is structurally similar to the IP3R but responds to different ligands (13). We and others have shown that the RYR is excluded from the apical region but localized to the basal region, importantly, where pancreatic zymogens, particularly proteases, are first activated during acute pancreatitis (8,14 …”