Aberrant Ca2+ signalling through acidic calcium stores in pancreatic acinar cells

Pancreatic acinar cells possess a very large Ca2+ store in the endoplasmic reticulum, but also have extensive acidic Ca2+ stores. Whereas the endoplasmic reticulum is principally located in the baso-lateral part of the cells, although with extensions into the granular area, the acidic stores are exclusively present in the apical part. The two types of stores can be differentiated pharmacologically because the endoplasmic reticulum accumulates Ca2+ via SERCA pumps, whereas the acidic pools require functional vacuolar H+ pumps in order to maintain a high intra-organellar Ca2+ concentration. The human disease acute pancreatitis is initiated by trypsinogen activation in the apical pole and this is mostly due to either complications arising from gall bladder stones or excessive alcohol consumption. Attention has therefore been focussed on assessing the acute effects of bile acids as well as alcohol metabolites. The evidence accumulated so far indicates that bile acids and fatty acid ethyl esters – the non-oxidative products of alcohol and fatty acids – exert their pathological effects primarily by excessive Ca2+ release from the acidic stores. This occurs by opening of the very same release channels that are also responsible for normal stimulus–secretion coupling, namely inositol trisphosphate and ryanodine receptors. The inositol trisphosphate receptors are of particular importance and the results of gene deletion experiments indicate that the fatty acid ethyl esters mainly utilize sub-types 2 and 3.