Bile Acids Induce Ca2+ Release from Both the Endoplasmic Reticulum and Acidic Intracellular Calcium Stores through Activation of Inositol Trisphosphate Receptors and Ryanodine Receptors

Abstract

Gallstones can cause acute pancreatitis, an often fatal disease in which the pancreas digests itself. This is probably because of biliary reflux into the pancreatic duct and subsequent bile acid action on the acinar cells. Because Ca 2؉ toxicity is important for the cellular damage in pancreatitis, we have studied the mechanisms by which the bile acid taurolithocholic acid 3-sulfate (TLC-S) liberates Ca 2؉ . Using two-photon plasma membrane permeabilization and measurement of [Ca 2؉ ] inside intracellular stores at the cell base (dominated by ER) and near the apex (dominated by secretory granules), we have characterized the Ca 2؉ release pathways. Inhibition of inositol trisphosphate receptors (IP 3 Rs), by caffeine and 2-APB, reduced Ca 2؉ release from both the ER and an acidic pool in the granular area. Inhibition of ryanodine receptors (RyRs) by ruthenium red (RR) also reduced TLC-S induced liberation from both stores. Combined inhibition of IP 3 Rs and RyRs abolished Ca 2؉ release. RyR activation depends on receptors for nicotinic acid adenine dinucleotide phosphate (NAADP), because inactivation by a high NAADP concentration inhibited release from both stores, whereas a cyclic ADPR-ribose antagonist had no effect. Bile acid-elicited intracellular Ca 2؉ liberation from both the ER and the apical acidic stores depends on both RyRs and IP 3 Rs.Bile acids, hydrophobic derivatives of cholesterol, have been suggested as a possible cause of acute pancreatitis (1). Many patients with acute pancreatitis have gallstones, blocking the ampulla of Vater, which may allow reflux of bile into the pancreatic duct system, leading to inflammation. It has been proposed that bile acids can trigger acute pancreatitis (2-4), and they have also been postulated to be tumor promoters (5), although the mechanism of action is not clear (6). Bile salts are known to induce severe experimental pancreatitis (7-9). Recent research points mainly toward abnormal calcium signaling as a possible cause of acute pancreatitis (10 -13) while casting doubt on the originally proposed ionophore-like mechanism of action of bile acids (14,15). Previous work has shown that application of bile acids can cause an increase in the levels of cytosolic [Ca 2ϩ ] in both hepatocytes (16,17) and pancreatic acinar cells (10). Specifically, bile acids activate calcium entry into the cell and cause depletion of internal calcium stores (12). Other effects not linked to calcium signaling (18) have also been observed, including an increase in the intracellular Na ϩ concentration (19) and depolarization of the inner mitochondrial membrane (20, 21).Ca 2ϩ signaling has been extensively studied in pancreatic acinar cells (22,23) and their organelles (24 -26). They are highly polarized, with distinct basal and apical poles. The secretory granules are confined to the apical region (27), which is surrounded by a perigranular Golgi apparatus and a mitochondrial belt (28, 29). All Ca 2ϩ signals start in the apical pole, and those elicited by low agonist concentrations are most...

Pancreatic protease activation by alcohol metabolite depends on Ca 2+ release via acid store IP 3 receptors

“…Our previous studies of 2-photon permeabilized acinar cells (21,22) showed the existence of 2 separate Ca 2ϩ stores, namely the ER and an acidic store. The ER maintains a high Ca 2ϩ concentration by action of a Ca 2ϩ pump, which can be specifically inhibited by TG (25) thereby depleting the ER of Ca 2ϩ due to leaks in the ER membrane (3,26).…”

“…Although the endoplasmic reticulum (ER) is the principal source of Ca 2ϩ released from internal stores in response to neurotransmitter or hormonal stimulation (3,15,16), Ca 2ϩ can also be liberated from acid stores (3,15,(17)(18)(19)(20)(21)(22). Several Ca 2ϩ -liberating agents release Ca 2ϩ from both thapsigargin (TG)-sensitive and bafilomycin (Baf)-sensitive acidic stores (21,22).…”

“…Several Ca 2ϩ -liberating agents release Ca 2ϩ from both thapsigargin (TG)-sensitive and bafilomycin (Baf)-sensitive acidic stores (21,22).…”

“…Using 2-photon permeabilized acinar cells (21,22), we show that palmitoleic acid ethyl ester (POAEE) releases Ca 2ϩ from both the TG-sensitive ER and the Bafsensitive acid store in the granular apical region. POAEE activates trypsin in pathophysiologically relevant concentrations and this activation depends on Ca 2ϩ release from the apical acid store, mainly through functional IP 3 receptors (IP 3 Rs) of types 2 and 3.…”

Bile acids inhibit Na+/H+ exchanger and Cl−/HCO3 − exchanger activities via cellular energy breakdown and Ca2+ overload in human colonic crypts

“…It was shown previously that the Cl -/HCO 3 -exchanger SLC26A3 and NHE3 are inhibited by the pathological increase of intracellular Ca 2+ [6,26]. In our experiments, CDC induced a dose- 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 the release from the ER via IP 3 R and/or RyR or Ca 2+ entry from the extracellular space [32,14,13] [26].…”