Discharge characteristics of nematocysts isolated from acontia of Calliactis parasitica

Experiments were performed on specimens of Calliactis parasitica collected near Plymouth in Apr 1987 and in the Mediterranean between Sep 1987 and Apr 1988. Undischarged nematocysts (basitrichous isorhizas) were separated from the acontia by using 1 M glycerol, 1 M citrate, 0.5% Nonidet or 0.5% Triton X-100 as isolating agents, or by freezing the acontial tissue. The mechanisms of extrusion were not studied. The effectiveness of 50 mM thioglycolate in discharging nematocysts isolated by the above methods and suspended in Ca- and Mg-free artificial sea water (ASW) was investigated. Nematocysts extruded in glycerol were more responsive to thioglycolate than those extruded in citrate. Capsules isolated in non-ionic detergents, however, and those obtained by freezing were not discharged by thioglycolate. If capsules extruded in glycerol were suspended in ASW and this was replaced with distilled water, they did not respond to thioglycolate.