Molecular Basis of P2-Receptor-Mediated Calcium Signaling in Activated Pancreatic Stellate Cells

Objectives: There is growing evidence that extracellular nucleotide-induced signaling confers to fibrogenesis in liver and pancreas. Pancreatic stellate cells (PSC) are the most important cell type in pancreatic fibrosis. P2 purine and pyrimidine receptors, again, are pivotal mediators of inflammatory and profibrogenic signals. Our aim was to elucidate the underlying signaling components in activated PSC. Methods: We performed expression analysis of calcium ion (Ca2+) signaling components and monitored real-time intracellular Ca2+ responses to nucleotides in rat PSC. Results: Adenosine monophosphate, adenosine diphosphate, and adenosine-5'-triphosphate elicited detectable rises in intracellular Ca2+ concentrations. Stimulation of PSC by ATP led to intracellular Ca2+ signals mediated through both P2X and P2Y receptors. Whereas uridine triphosphate-mediated Ca2+ signals were generated by activation of P2Y receptors only, uridine diphosphate stimulated P2X receptors as well. Of the phospholipase C (PLC)/inositol-1,4,5-trisphosphate pathway, all PLC-facilitating G alpha subunits were present in activated cells as were all 3 inositol-1,4,5-trisphosphate receptor isoforms. In addition, transcripts of PLC-beta and PLC-delta isoforms were also strongly detectable. Conclusions: Activated PSC feature a plethora of elements from the Ca2+ signaling toolkit and functionally express a subset of P2 nucleotide receptors. Purines and pyrimidines elicit robust intracellular Ca2+ signals likely contributing to the fibrogenetic potential of these cells.