Involvement of cyclic nucleotides and IP₃ in the regulation of luminescence in the brittlestar <i>Amphipholis squamata</i> (Echinodermata)

We investigated the effects of cyclic nucleotides (cGMP, cAMP) and the phosphoinositide IP3 on the luminescence of the ophiuroid Amphipholis squamata. The cGMP analogue, dibutyryl-cGMP, and the guanylate cyclase activator, sodium nitroprusside, had no effect on the luminescence. The cAMP analogue, dibutyryl-cAMP, and the adenylate cyclase activator, forskolin, triggered luminescence. Moreover, the adenylate cyclase inhibitor, MDL-12330A, significantly reduced ACh-induced luminescence. The phospholipase C inhibitor, U-73122, also significantly reduced ACh-induced luminescence. The results suggest that ACh-induced luminescence is mediated by both cAMP and IP3 pathways but not by cGMP. The effects of calcium-free ASW confirmed this hypothesis. A hypothetical scheme of the transduction mechanisms involved in the intracellular control of luminescence is presented