Although methionine sulfoxide reductase (Msr) is known to modulate activity of multiple functional proteins, roles of Msr in pancreatic stellate cell physiology have not been reported. In the present work we investigated expression and function of Msr in freshly isolated and cultured rat pancreatic stellate cells. Msr expression was determined by RT-PCR, Western blot and immunocytochemistry. Msr over-expression was achieved by transfection with adenovirus vectors (1012 vg.mL-1 x 5 microL, to each well of 6-well plates). Pancreatic stellate cells were co-cultured with pancreatic acinar cells AR4-2J in monolayer culture. Pancreatic stellate and acinar cell function was monitored by Fura-2 calcium imaging. Rat pancreatic stellate cells were found to express MsrA, B1, B2, their expressions diminished in culture (P < 0.05, N = 3-4, by Student’s T test). Over-expressions of MsrA, B1, or B2 were found to enhance ATP (10 microM)-stimulated calcium increase (P < 0.05, N = 3) but decreased reactive oxygen species production (P < 0.05, N = 3) and lipopolysaccharide-elicited IL-1 production (from 1067 ± 24 to 537 ± 72, 211 ± 41, 286 ± 35 ng.L-1 respectively, in mean ± SEM, with P < 0.05, N = 3). Pancreatic stellate cell-co-culture with AR4-2J blunted cholecystokinin (CCK 20, 60, 200 pM)- and acetylcholine (ACh 20, 60, 200 nM)-stimulated calcium increases in AR4-2J (P < 0.05, N = 3), depending on acinar / stellate cell ratio (2, 10, 50)(P < 0.05, N = 3), this inhibition was reversed by MsrA, B1 over-expression in stellate cells (P < 0.05, N = 3) or by Met supplementation (2, 10, 50 mM) in the co-culture medium (P < 0.05, N = 3). These data together suggest that Msr play important roles in pancreatic stellate cell function and the stellate cells may serve as a brake mechanism on pancreatic acinar cell calcium signaling subject to modulation by stellate cell Msr expression.