Settlement and metamorphosis of Capitella larvae induced by juvenile hormone-active compounds is mediated by protein kinase C and ion channels

The signal transduction pathway by which juvenile hormone-active compounds induce settlement and metamorphosis of metatrochophore larvae of the polychaete annelid Capitella sp. 1 was investigated. The known protein kinase C (PKC) activator phorbol-12,13-dibutyrate was an active inducer of settlement and metamorphosis, whereas H-7, an inhibitor of PKC, inhibited settlement and metamorphosis in response to juvenile hormone III (JH III). JH III and methyl farnesoate (MF) also directly activated, in vitro, both a PKC-like enzyme present in Capitella homogenates and PKC purified from rat brain. In addition, binding studies using the fluorescent PKC inhibitor RIM-1 revealed the presence of a PKC-like enzyme in intact Capitella larvae and juveniles. Settlement and metamorphosis of the larvae was also stimulated by membrane-depolarizing concentrations of KCl. This response to KCl was inhibited by tetraethylammonium. The potassium channel blocker it-aminopyridine induced settlement and metamorphosis, whereas settlement and metamorphosis in response to JH III was inhibited by the potassium channel ionophore nigericin. Settlement and metamorphosis induced by JH III was inhibited by the calcium channel blockers Ni2+, Zn2+, and verapamil, whereas settlement and metamorphosis was induced by the calcium ionophore A23187. These results suggest that in mediating this response, juvenile hormones may cause activation of PKC, leading to subsequent modulation of potassium and calcium channels.