SM709, Ingredient of Antimelanogenic Bamboo Extract, Blocks Endothelin-1-induced $[Ca^{2+}]_i$ Increase in Human Melanocytes

Endothelins secreted from keratinocytes are intrinsic mitogens and melanogens of human melanocytes in UVB-induced hyperpigmentation. To elucidate the cellular mechanism of antimelanogenic activity of bamboo extract, the effects of three ingredients of bamboo extract on endothelin 1 (ET-1)-induced $Ca^{2+}$ mobilization were investigated in cultured human melanocytes. ET-1 receptors in human melanocytes were characterized by using specific antagonist, and ET-1 was found to increase intracellular $Ca^{2+}$ concentration ($[Ca^{2+}]_i$) by activating ET-B receptor. SM709 (1,2-O-diferulyl-glycerol), an ingredient of bamboo extract, inhibited ET-1-induced $[Ca^{2+}]_i$ increase in a concentration- and time-dependent manner, although another ingredients SM707 and SM708 had no effect on ET-1-induced $[Ca^{2+}]_i$ increase in human melanocytes. SM709 ($100{\mu}M$), however, did not affect $[Ca^{2+}]_i$ increase induced by thapsigargin and caffeine, suggesting that SM709 has no effect on the $Ca^{2+}$ store in melanocytes. Furthermore, SM709 did not affect $[Ca^{2+}]_i$ increase induced by LPA or ATP, known as G protein-mediated PLC activators like ET-1. Taken together, it is suggested that SM709 antagonizes ET-1-induced transmembrane signaling through ET-B receptor, which maybe a possible underlying mechanism of antimelanogenic activity of bamboo extract in human melanocytes.