EVIDENCE FOR THE INVOLVEMENT OF CYCLIC-AMP IN THE PHEROMONAL MODULATION OF BARNACLE SETTLEMENT

The involvement of cyclic AMP in the settlement of the cypris larva of Balanus amphitrite amphitrite Darwin has been examined through the us e of compounds that affect intracellular cyclic AMP levels. The activa tion of adenylate cyclase with forskolin, and the inhibition of phosph odiesterase with 3-isobutyl-1-methylxanthine, caffeine and theophyllin e, significantly increased the settlement of cyprids. Although the ana logue dibutyryl cyclic AMP appeared to increase settlement, the effect was not significant. No marked increase in settlement resulted from t he incubation of cyprids with dibutyryl cyclic GMP, 8-(4-chlorophenylt hio) (CPT) cyclic AMP or papaverine (a phosphodiesterase inhibitor), M iconazole nitrate, an adenylate cyclase inhibitor, prevented settlemen t, but this effect appeared to be physico-chemical rather than pharmac ological. Radioimmunoassay did not clearly show whether cyclic AMP lev els changed following exposure of cyprids to a pulse of crude barnacle extract, However, exposure to forskolin significantly increased the c yclic AMP titre of cyprids, We conclude that compounds that alter intr acellular cyclic AMP levels alter normal patterns of cyprid settlement , Whether this is because of an alteration in signal transduction is u nclear.