Inhibition of ⁴⁵Ca²⁺ uptake in the eggs and embryos of the sea urchin, <i>Anthocidaris crassispina</i>, by several calcium antagonists, anion transport inhibitor, and chloride transport inhibitors

<jats:title>Abstract</jats:title><jats:p>The rate of<jats:sup>45</jats:sup>Ca<jats:sup>2+</jats:sup> uptake was close to zero in unfertilized eggs. It rapidly increased after fertilization and then decreased within 1 hr. The rate remained low between 1 and 12 hr after fertilization (until shortly after hatching). Thereafter, the rate gradually increased during developmental period between 15 (the mesenchyme blastula stage) and 30 hr after fertilization (the prism stage). It then decreased 40 hr after fertilization (the pluteus stage). In embryos assayed 30 and 40 hr after fertilization, about 70 and 40 percent, respectively, of <jats:sup>45</jats:sup>Ca<jats:sup>2+</jats:sup> was found in the spicules. During the whole period of early development, <jats:sup>45</jats:sup>Ca<jats:sup>2+</jats:sup> uptake was inhibited by diltiazem and verapamil (calcium antagonists), ruthenium red (known to inhibit<jats:sup>45</jats:sup>Ca<jats:sup>2+</jats:sup> uptake in mitochondia and also Ca<jats:sup>2+</jats:sup> ‐ATPase in plasma membrane), and 4,4′‐diisothiocyano‐2,2′‐disulfonic acid stilbene (an anion transport inhibitor). Ethacrynic acid and furosemide (chloride transport inhibitors), inhibited <jats:sup>45</jats:sup>Ca<jats:sup>2+</jats:sup> uptake between 24 and 40 hr after fertilization. These results suggest that <jats:sup>45</jats:sup>Ca<jats:sup>2+</jats:sup> is transported through a Ca<jats:sup>2+</jats:sup> channel and/or a Ca<jats:sup>2+</jats:sup> ‐pump and that electrosilent transport of Ca<jats:sup>2+</jats:sup> is achieved by anion transport.</jats:p>