Calcium involvement in the luminescence control of three ophiuroid species (Echinodermata)

Although it has been shown that calcium is involved in the control of the luminous reaction of many invertebrate phyla, its role in Echinoderms is poorly documented. The aim of this work was to carry out a comparative study of calcium requirement of KCl-induced light emission by arm segments and dissociated luminous cells from three ophiuroid species, Ophiopsila californica, O. aranea and Amphiura filiformis. Results show a gradual inhibition of the luminescence when preparations are incubated in artificial sea water with lowered calcium concentration. The calcium substitutes Ba(2+) and Sr(2+) could act either as blockers or as substitutes, depending on the ophiuroid species; while calcium blockers Co(2+), Ni(2+) and Cd(2+) inhibit light emission in A. filiformis and in O. californica, but not in O. aranea. The nature of putative calcium voltage-gated channel has been studied pharmacologically using 1,4-dihydropyridine, benzodiazepine, phenylalkylamine and trifluoroperazine. From our results, it is proposed that calcium could act via an L-type voltage-gated calcium channel in O. californica and A. filiformis but not in O. aranea. The precise role of calcium in luminescence control still remains unknown; it could act as a second messenger or as a co-factor of the luminous reaction.