Cultured human melanocytes and non-metastatic 1F6 melanoma cells, which express functional sGC but low activities of GC-A/GC-B, responded to a long-term exposure to hypergravity (up to 5 g for 24 h) with elevated cGMP efflux in the presence of 0.1 mM 3-isobuthyl-1-methylxanthine, a non-specific PDE inhibitor [80], as well as in the presence of a direct NO donor [84]. The gene discussed is GCA; the disease is melanoma.