Melittin-induced alteration of epidermal adenylate cyclase responses

Using an in vitro pig skin-slice incubation system, we investigated the effect of melittin, a phospholipase A2 (PLA2) stimulator, on the adenylate cyclase-cyclic AMP (cAMP) system. Significant decreases of various epidermal (beta-adrenergic, adenosine, and histamine) adenylate cyclase responses were observed as early as 1 h following the melittin treatment (50 micrograms/ml). The effect of melittin was concentration-dependent and the minimal concentration of melittin was 10 micrograms/ml for the inhibition of the beta-adrenergic adenylate cyclase response, whereas more than 50 micrograms/ml concentration was required for the inhibition of the adenosine and histamine adenylate cyclase responses. There was no significant difference in either low or high Km cAMP phosphodiesterase activity between control and melittin-treated skin. The beta-adrenergic augmentation effect by various chemicals (colchicine and Ro10-1670, an active form of Ro10-9359) were suppressed by the simultaneous addition of melittin in the incubation medium. Our data indicate that melittin affects not only on the beta-adrenergic adenylate cyclase system but also on the adenosine and histamine adenylate cyclase systems. However, the beta-adrenergic system was shown to be more sensitive to melittin than the other receptor adenylate cyclase systems.