Abstract
Abstract Using split-fin preparations of the tilapia, Oreochromis niloticus, the effects of various drugs affecting the signal transduction pathway on MCH-induced aggregation of melanosomes were examined. A phospholipase C inhibitor (neomycin sulphate), protein kinase C (PKC) inhibitors (H-7 and staurosporine), PKC activators (SC-9 and TPA) and calmodulin inhibitors (W-7 and W-5) did not block melanophore response to MCH. However, forskolin, an adenylate cyclase stimulating drug, diminished MCH-induced aggregation of melanosomes in a dose-dependent manner. In fact, intracellular concentration of cyclic AMP (cAMP) in MCH (10 nM)-treated melanophores was found to be about 54% of the control level in melanophores immersed in physiological saline. These results suggest that cAMP is the second messenger for MCH action. Since okadaic acid at 10 μM perfectly inhibited melanosome-aggregating response to MCH, the involvement of protein phosphatase 2B in the response was also implied. In addition, the effects of se...
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