Fig. 4. Effects of S1P and PD98059 on melanogenesis in Mel-Ab cells. (A) Cells were cultured with 10 µM S1P and/or 20 µM PD98059 for 5 days, and phase contrast pictures were taken using a color video camera. The cells were pretreated with 20 µM of PD98059 for 1 hour and then cultured with 10 µM of S1P for 5 days, and tyrosinase activity (B) and melanin content (C) were measured, as described in Materials and Methods. Values indicate the mean of three independent experiments ± s.d.