Contribution of intracellular Ca2+ concentration and protein dephosphorylation to the induction of dopamine release from PC12 cells by the green odor compound hexanal.

n-Hexanal (hexanal), a straight-chain six-carbon aldehyde, is mainly present in plants. Hexanal strongly affects the release of dopamine from rat striatal slices and rat pheochromocytoma (PC12) cells. In this study, we attempted to clarify the mechanism underlying the regulation of dopamine release by hexanal by using PC12 cells, which have the ability to synthesize, store, and release dopamine. The stimulation of PC12 cells with hexanal enhanced dopamine release in a time- and dose-dependent manner. Dopamine release was partially inhibited by pretreatment of the cells with BAPTA-AM, a cell-permeable Ca2+ chelator. In addition, the intracellular Ca2+ concentration was found to slowly increase after hexanal stimulation. Furthermore, the Src tyrosine kinase inhibitor PP2 partially inhibited hexanal-induced dopamine release. However, the levels of phosphorylated proteins decreased after hexanal stimulation. Hexanal stimulated the release of only a small amount of dopamine from reserpine-treated PC12 cells, in which the vesicular dopamine was depleted. These findings suggest that both an increase in the intracellular Ca2+ concentration and the dephosphorylation of phosphorylated proteins might be required for hexanal-stimulated release of dopamine, and that the dopamine released because of hexanal stimulation mainly comes from the dopamine vesicles. This study showed the cellular events that occurred in PC12 cells after stimulation of hexanal. Furthermore, it is important to examine the relationship between the cellular functions and the physiological effects of hexanal on dopamine release.