Adult melanocytes typically have a very slow doubling time, especially in comparison to neonatal melanocytes. Endothelin-3 (ET-3) is added to adult melanocytes only to improve the doubling time and, in the process, help to maintain the cells as proliferating melanocytes. The neonatal melanocytes typically do not need additional assistance in order to remain proliferative, however culturing neonatal melanocytes with ET-3 should not cause issues.