CALCIUM CONTROL OF METAMORPHOSIS IN POLYCHAETE LARVAE

The importance of Ca2+ in the control of metamorphosis of a marine inv ertebrate larva was investigated. An excess of [Ca2+] in the external medium induced metamorphosis of Phragmatopoma californica (polychaete) larvae in a concentration-dependent manner. This effect is specific f or calcium, and not simply the result of osmotic changes, as an excess of Mg2+ did not induce metamorphosis. Consistent with this finding, t he calcium ionophore, A23187, also induced metamorphosis in a concentr ation-dependent manner. Paradoxically, however, the aromatic compounds diltiazem, verapamil, D600, and nifedipine, known to block Ca2+ chann els in other systems, also induced metamorphosis. When exposed to dilt iazem for only 20 h and subsequently washed free of this compound, 95% of the larvae metamorphosed and developed normally. Previous studies have demonstrated that the induction of metamorphosis in Phragmatopoma californica is controlled by chemosensory recognition of an exogenous morphogen and mediated by an excitatory pathway that involves adenyl cyclase and cyclic AMP. Because cellular excitation and cyclic AMP-dep endent signal transduction generally involve the participation of calc ium ion, the most parsimonious explanation for the results reported he re include (1) direct control of the morphogenetic pathway by calcium ion, and (2) complexities of the calcium regulation of this process, o r a functional similarity between the structurally related aromatic ef fectors tested and the natural inducer of metamorphosis. (C) 1993 Wile y-Liss, Inc.