INTRACELLULAR CALCIUM TRANSIENTS DURING NEMATOCYST DISCHARGE IN ACTINULAE OF THE HYDROID, TUBULARIA-MESEMBRYANTHEMUM

The discharge of atrichous isorhiza (AI) from the aboral tentacle tips (ATT) is an integral process during settlement of actinula larvae of the marine hydroid Tubularia mesembryanthemum, since discharged adhesi ve tubules from AI anchor actinula to settlement substrata. Under expe rimental conditions, AI discharge was triggered either by contact with bacterial film-coated micropipettes or by exposure to artificial seaw ater (ASW) containing high concentrations of K+ ions (K+-ASW). Trigger ing of AI discharge required both contact by ATT with the substrata an d the presence of Ca2+ ions in the bathing solution. Changes in intrac ellular Ca2+ ion concentration ([Ca2+](i)) were monitored by measuring fluorescence images obtained from ATT of intact actinulae loaded with fura-2. An initial low [Ca2+](i) (R-340/380=1.0) value was rapidly el evated by K+-ASW treatment (R-340/380=1.9) and simultaneously accompan ied by AI discharge. These results suggest that Ca2+ ions present in t he bathing solution flow into nematocytes during AI discharge process. (C) 1997 Wiley-Liss, Inc.