We conclude that high concentrations of FFA as present in the plasma of LPL-deficient mice and in patients with HTG lead to pancreatic cell damage and are high risk factors for the development of acute pancreatitis. In addition to its enzymatic effect which leads to the generation of cell-damaging FFA from triglycerides, pancreatic lipase also prevents Ca(2+) overload in pancreatic acinar cells and, therefore, counteracts cell injury.

LPL-deficient mice with severe hypertriglyceridaemia display enhanced susceptibility to acute pancreatitis. High levels of chylomicrons and free fatty acids result in pancreatic cell injury. Pancreatic lipase has a dual effect: generating free fatty acids from chylomicrons and preventing Ca(2+) overload in pancreatic acinar cells.

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Abstract

Cyclic ADP-ribose, a metabolite of NAD ؉ evokes Ca 2؉ release from intracellular stores in different cells. We have determined the activity of cADPr-producing enzymes (ADP-ribosyl cyclases) in different cellular fractions prepared from isolated pancreatic acinar cells by measuring the conversion of the ␤-NAD ؉ analogs 1,N 6 -etheno-NAD and nicotinamide guanine dinucleotide to the fluorescent products 1,N 6 -etheno-cADPr and cyclic GDP-ribose, respectively. Substrate/product analyses were carried out by reverse-phase high pressure liquid chromatography. In all subcellular fractions examined (cytosol, mitochondria, plasma, and intracellular membranes), ADP-ribosyl cyclase activity was detected except in zymogen granular membranes. Western blot analysis and immunoprecipitation experiments revealed the presence of the ADP-ribosyl cyclase CD38 in both plasma membranes and mitochondria but not in the cytosol. Hormonal stimulation of intact acinar cells for 1 min with acetylcholine (ACh), cholecystokinin (CCK), or a membrane-permeant analog of cGMP increased ADP-ribosyl cyclase activity in the cytosol by 1.8-, 1.6-, and 1.9-fold, respectively, as compared with the control but had no effect in any other fraction. Both ACh and CCK also increased accumulation of cGMP in the cells by about 2-fold. Bombesin had no significant effect on either ADP-ribosyl cyclase activity or cGMP accumulation within this short period of stimulation. We conclude that at least two types of ADP-ribosyl cyclases are present in pancreatic acinar cells: membrane-bound CD38 and a cytosolic enzyme different from CD38. Stimulation of pancreatic acinar cells with CCK or ACh results in exclusive activation of the cytosolic ADP-ribosyl cyclase activity, most likely mediated by cGMP.Hormonal stimulation of pancreatic acinar cells stimulates production of inositol 1,4,5-trisphosphate (IP 3 ) 1 with a consequent release of Ca 2ϩ from intracellular Ca 2ϩ stores (1). This leads to an increase in cytosolic [Ca 2ϩ ], which propagates from the luminal to the basolateral cell pole as a Ca 2ϩ wave (2-4). In addition to IP 3 -induced Ca 2ϩ release, also Ca 2ϩ -induced Ca 2ϩ release exists in pancreatic acinar cells (2, 5, 6). The Ca 2ϩ wave velocity (7) depends on the secretagogue that is used to maximally stimulate the cell (3, 7, 8), indicating that different extracellular stimuli may utilize a different set of second messengers.Cyclic adenosine diphosphoribose (cADPr) leads to Ca 2ϩ release from intracellular stores of sea urchin eggs (9) and from different mammalian cell types (reviewed in Ref. 10) including cells from the exocrine (5) and endocrine (11) pancreas. In pancreatic acinar cells, cADPr applied to the cell via a patch pipette induced Ca 2ϩ oscillations (5) and Ca 2ϩ release from intracellular stores when applied to permeabilized cells (12,13).Production of cADPr, activated by extracellular signals, has been shown only in a limited number of cell types, e.g. in pancreatic islets (11), smooth muscle cells (14), cardiac myocytes (15), cortical astrocy...