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Journal of Experimental Biology 156,173-185 (1991)
Published by Company of Biologists 1991

The Discharge Of in Situ Nematocysts of the Acontia of Aiptasia Mutabilis is a Ca2+-Induced Response

GIUSEPPE SANTORO 1 and ALBERTO SALLEO 1

1 Institute of General Physiology, University of Messina, Via Sperone 31, 98010 Messina, Italy

The ionic events leading to discharge of in situ nematocysts were investigated in acontia excised from Aiptasia mutabilis Gravenhorst. The effect on discharge of various ionic solutions and ion channel blockers was tested. In the absence of Ca2+ in the medium no discharge was elicited, whatever the composition of the medium. In the presence of 10 mmoll-1 Ca2+ total discharge was induced by NaSCN, NaI, choline iodide and KI, whereas KC1 induced both discharge and extrusion of undischarged nematocysts. The latter effect was prevented by La3+ but not by 4-aminopyridine (4-AP) and tetraethylammonium (TEA+). Alcian Blue induced total discharge. NaCl and choline chloride were ineffective. The discharge induced by lyotropic anions depended on Ca2+ concentration and was prevented by the Ca2+ channel blockers La3+, Co2+ and Cd2+, but not by verapamil. It is proposed that the discharge of in situ nematocysts is caused by Ca2+ conductance through the cell membrane of either the nematocyte or the supporting cell. Furthermore, cyclic AMP and cyclic GMP do not seem to be involved as second messengers in the discharge process. The combined effects of the metabolic poisons dinitrophenol (DNP) and monoiodoacetic acid did not affect the discharge process.

Key words: nematocytes, discharge, Ca2+, Aiptasia mutabilis

Accepted on September 11, 1990






© The Company of Biologists Ltd 1991