Probable Role of Allylisothiocyanate‐Sensitive H⁺, K⁺‐ATPase in Spicule Calcification in Embryos of the Sea Urchin, Hemicentrotus pulcherrimus

In embryos of the sea urchin, Hemicentrotus pulcherrimus , as well as in cultured cells derived from isolated micromeres, spicule formation was inhibited by allylisothiocyanate, an inhibitor of H + , K + ‐ATPase, at above 0.5 μM and was almost completely blocked at above 10 μM. Amiloride, an inhibitor of Na + , H + antiporter, at above 100 μM exerted only slight inhibitory effect, if any, on spicule formation. Intravesicular acidification, determined using [ dimethylamine ‐ 14 C]‐aminopyrine as a pH probe, was observed in the presence of ATP and 200 mM KCl in microsome fraction obtained from embryos at the post gastrula stage, at which embryos underwent spicule calcification. Intravesicular acidification and K + ‐dependent ATPase activity were almost completely inhibited by allylisothiocyanate at 10 μM. Allylisothiocyanate‐sensitive ATPase activity was found mainly in the mesenchyme cells with spicules isolated from prisms. H + , K + ‐ATPase, an H + pump, probably mediates H + release to accelerate CaCO 3 deposition from Ca 2+ , CO 2 and H 2 O in the primary mesenchyme cells. Intravesicular acidification was stimulated by valinomycin at the late gastrula and the prism stages but not at the pluteus stage. K + permeability probably increases after the prism stage to activate H + release.