EVIDENCE FOR THE INVOLVEMENT OF CYCLIC AMP IN THE METAMORPHOSIS OF BAY SCALLOP, ARGOPECTEN IRRADIANS (LAMARCK) LARVAE.

The putative involvement of cyclic AMP (cAMP) in the metamorphosis of bay scallop Argopecten irradians larvae has been investigated on three integrated aspects. First, we conducted experiments on response of competent larvae to selective inhibitors of phosphodiesterase (PDE), theophylline, and caffeine, which presumably lead to elevated concentration of intracellular cAMP by preventing the degradation of cAMP to 5′-AMP. Second, the endogenous levels of cAMP were determined during larval development. Third, monitoring the variation of cAMP content in larvae when exposed to neuroactive compounds tested (L-DOPA and epinephrine) and to elevated concentrations of potassium ion, was carried out to examine the possible role of cAMP as a second messenger in metamorphic pathway stimulating artificially. Consistent results have been obtained in all the three experiments. The two putative PDE inhibitors that were tested stimulated metamorphosis in A. irradians larvae significantly above control level in a dosage-dependent manner. The inductive effects did not vary significantly with exposure time. At the optimum concentration of 1.0 mM, percent metamorphosis increased by 33% and 36.01% when subjected to theophylline and caffeine respectively. The endogenous level of cAMP varied dramatically over larval development. In particular, significant increase in cAMP content from 2129 pmol/(mg protein) for eyed larvae (Day 13 post-fertilization, PF) to 15,195 pmol/(mg protein) for spats (Day 17 PF) occurred during the metamorphic process. This finding indicates that metamorphic pathway involves cAMP in appreciable quantities. Furthermore, the endogenous cAMP content increased significantly in competent larvae exposed to excess potassium ion, epinephrine, or L-DOPA,... [ABSTRACT FROM AUTHOR]