Melatonin induces calcium mobilization and influences cell proliferation independently of MT1/MT2 receptor activation in rat pancreatic stellate cells

Melatonin, the product of the pineal gland, possesses antioxidant, anti-inflammatory, and antitumor properties in different tissues, in addition to its role as regulator of biological rhythms. In this study, the effects of pharmacological concentrations of melatonin (1 mu M-1 mM) on pancreatic stellate cells (PSCs) have been examined. Cell viability was studied using AlamarBlueA (R) test. Cell-type specific markers and total amylase content were analyzed by immunocytochemistry and colorimetric methods, respectively. Changes in intracellular free Ca2+ concentration were followed by fluorimetric analysis of fura-2-loaded cells. The cellular red-ox state was monitored following CM-H(2)DCFDA-derived fluorescence. Determination of the activation of p44/42 mitogen-activated protein kinase (MAPK), SAPK/JNK and p38 was measured by Western blot analysis. Our results show that PSCs viability decreased in the presence of 100 mu M or 1 mM melatonin. However, in the presence of 1 or 10 mu M melatonin, no changes in cell viability were observed. Melatonin MT1 and MT2 receptors could not be detected. Melatonin induced Ca2+ mobilization from intracellular pools. In the presence of melatonin, activation of crucial components of MAPKs pathway was noticed. Finally, the indole did not change the oxidative state of PSCs, but exerted a protective effect against H2O2-induced oxidation. We conclude that melatonin, at pharmacological concentrations, might regulate cellular proliferation of PSCs independently of specific plasma membrane receptors.