Pharmacological control of ciliary activity in the young sea urchin larva. Studies on the role of Ca2+ and cyclic nucleotides.

The ciliary stimulation by monoamines is enhanced by adenylcyclase activators and a phosphodiesterase inhibitor indicating that cAMP is a mediator, a conclusion supported by the effects of db-cAMP. The role of cGMP is also examined. When stimulation exceeds certain levels, it is overpowered by some inhibitory feedback mechanism. The effects of altered Ca2+ concentrations, Ca2+ antagonists and a Ca2+ ionophore suggest that Ca2+ is involved in ciliary excitation as well as in the inhibitory mechanism. These suggestions are examined by experiments on the influence of altered Ca2+ concentrations and of the phosphodiesterase inhibitor on the response to various agents.