Role of protein kinase C, G-protein coupled receptors, and calcium flux during metamorphosis of the sea urchin Strongylocentrotus purpuratus. Artificial inducers have been used to study signal-transduction pathways involved in metamorphosis of some marine invertebrates. However, the transduction mechanisms for echinoderms have been less explored. In the present study, participation of protein kinase C (PKC), G-protein-coupled receptors (GPCRs), and calcium has been investigated during metamorphosis of the sea urchin Stronglylocentrotus purpuratus. Competent larvae were induced with different drugs that activate (PKC and GP activators, Ca2+ ionophores, and inhibitors of Ca2+ ATPase) or inhibit (PKC, G-protein, and Ca2+ flux inhibitors) metamorphosis. Six of the compounds were effective: the PKC activators TPA and indolactam; the G-protein inhibitors suramin and guanosine; the calcium ionophore A23187, and the calcium ATPase inhibitor thapsigargin. TPA was effective at 0.001 microM; indolactam was effective at 0.001 microM. In the presence of KCl as inducer, the G-protein inhibitor suramin was effective at 10 microM and guanosine at 0.001 microM. In the presence of a bacterial film as inducer, suramin was effective at 50 microM, and guanosine inhibited metamorphosis at 1 microM. A23187 was effective at 5 and 10 microM and thapsigargin at 50 and 100 microM. Our results indicate that GPCRs, protein kinase C, and calcium participate in the metamorphosis of S. purpuratus. These elements of the transduction pathways triggered during metamorphosis may be part of a cascade of signal transduction routes that interact from induction to the end of the morphogenetic events that shape the postlarval form. In addition, according to the results obtained with G-protein inhibitors, the GPCRs may be shared between the artificial (KCl) and natural (biofilm) inducers.