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.