Objective To study the effects of nicotinamide on the human skin melanocytes and try to explore the potential mechanism of nicotinamide on the calcium signal transduction,cytoskeleton.Methods The primary cultured human skin melanocytes from foreskin were selected as the target cells in the present study.0.00,0.05,0.25,1.25 and 6.25 mg/ml nicotinamide were applied respectively.Western blot,fluorescent probes(Flu-3AM),flow cytometry analysis and time-lampse microscope digital skill were used to evaluate the effects of nicotinamide on melanosome motility and the melanosome distribution in melanocytes.Results The results showed that nicotinamide had a potential effect on regulating free calcium concentration in a dose-dependent manner(y=76.461 2-5.435x,r=0.97);The activity of Na+-K+-Ca2+-ATPase was down regulated with the increasing concentration of nicotinamide.The expression of cellular dynein was also altered by nicotinamide;Na +-K+-Ca2+-ATPase activity was kept normal when given 0.05,0.25 mg/ml nicotinamide,while the dynein protein expression was inhibited(P