Hyposmotic shock-induced discharge in acontia ofCalliactis parasitica is blocked by gadolinium

On acontia ofCalliactis parasitica it was observed that mechanical stimuli applied by a gelatin probe, a method effective in tentacles of Anthozoa, do not induce the discharge of nematocytes. Hyposmotic shock, performed by treatment with NaCl solution 35% hyposmotic with respect to sea water, induces, in the presence of Ca²⁺, the discharge that spreads along the acontial filament, as previously observed following treatment with SCN^–. The hyposmotic shock-induced discharge is blocked by Gd³⁺ at a concentration of 1 M. 10 M Gd³⁺ prevents also the SCN^–-induced discharge. These results suggest the presence of stretch activated cation channels either in nematocytes and/or in supporting cells as well as a possible effect of SCN^– on this class of ion channels.