TOXIC GLOBALISATION OF SECRETAGOGUE-ELICITED ACINAR CELL CA2+ SIGNALING AND PREVENTION BY ATP OR REMOVAL OF CA2+ FROM THE CELL EXTERIOR

Abstract

Background & Aims: We have previously demonstrated that low concentrations of the pancreatic acinar cell toxins taurolithocholic-3-sulphate (TLCS) or palmitoleic acid ethyl ester (POAEE) induce toxic globalisation of inositol trisphosphate (IP3)-mediated signaling increases in the cytosolic calcium ion concentration ([Ca2+]C, IP3 applied via patch pipette). We sought to determine whether toxic globalisation of [Ca2+]C can occur with physiological secretagogues, and how it can be prevented. Methods: Isolated mouse pancreatic acinar cells were examined by confocal microscopy to measure changes in [Ca2+]C (Fluo4-AM), mitochondrial function (NADH autofluorescence), ATP concentration (Mg Green) and cell fate (propidium iodide, PI). Cholecystokinin (CCK, 1-20 pM) or acetylcholine (ACh, 50 nM) were perfused extracellularly and low concentrations (10 mM) of TLCS or POAEE added, while whole-cell recordings of Ca2+-dependent Cl− currents were made. In some experiments, supplementary ATP was added to the internal pipette solution. Results: CCK and ACh elicited typical [Ca2+]C signals in the granular pole with stimulus-metabolism coupling (NADH). Extracellular TLCS or POAEE (10 mM) transformed these signals into prolonged (>30 s), global [Ca2+]C increases accompanied by NADH and ATP depletion, inducing necrosis. Supplementary ATP reduced the period of globalisation associated with each elevation of [Ca2+]C and prevented necrosis, as did removal of Ca2+ from the external medium, and in the case of POAEE, hydrolase inhibition, preventing POA formation. Conclusion: Physiological Ca2+ signals elicited by secretagogues can undergo toxic globalisation from low concentrations of acinar cell toxins, resulting in mitochondrial Ca2+ overload, inhibition of ATP production and cell death. Cell injury could be prevented by blockade of Ca2+ entry.