Involvement of cyclic nucleotides and IP(3) in the regulation of luminescence in the brittlestar Amphipholis squamata (Echinodermata).

We investigated the effects of cyclic nucleotides (cGMP, cAMP) and the phosphoinositide IP(3) 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 IP(3) 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.