Mechanisms of action of melanin-concentrating hormone in the teleost fish erythrophoroma cell line (GEM-81)

Melanin-concentrating hormone (MCH) evokes an increase of GEM-81 cell proliferation. This action of 10 −6 M MCH was inhibited in the presence of the following blockers: U-73122 (phospholipase C), Ro-31-8220 (PKC) or KN-93 (Ca 2+/calmodulin-dependent kinase). The more selective PKC inhibitors, HBDDE and Go-6983, which block, respectively, PKC α/γ isoform and β1 isoform, were used. HBDDE was ineffective whereas Go-6983 reversed the proliferative response promoted by MCH. Flow cytometry assays demonstrated that MCH induces a slow and long-lasting rise in intracellular calcium, which can be blocked by U-73122. Our results also show a cAMP increase evoked by MCH. Our data support the assumption that MCH exerts its effect on GEM-81 erythrophoroma cells through activation of phosholipase C, β1 PKC, and Ca 2+/calmodulin-dependent PKC, and eliciting a slow, long-lasting rise in calcium, which may trigger the proliferative signal.