Ionic status, calcium uptake, and Ca2Â +-ATPase activity during early development in the purple sea urchin (Strongylocentrotus purpuratus)

Ionic status during early development was investigated in the purple sea urchin. Whole body cation concentrations (Ca2 +, Na+, K+, Mg2 +), unidirectional Ca2 + uptake rates measured with 45Ca2 +, Ca2 +-ATPase activity, and growth were examined at 12 h intervals over the first 96 h of development. Whole body Ca2 + concentration was low initially but increased steadily by > 15-fold through to the pluteus stage. Whole body Mg2 +, K+ and Na+ levels exhibited diverse patterns, but all increased at 72-96 h. Ca2 + uptake rates were low during initial cell cleavages at 12 h but increased greatly at blastulation (24 h) and then again at gastrulation (48 h), declining thereafter in the pluteus stage, but increasing slightly at 96 h. Ca2 +-ATPase activity was initially low but increased at blastulation through gastrulation (24-48 h) but declined thereafter in the pluteus stage. Embryonic weights did not change over most of development, but were significantly higher at 96 h. Overall, the gastrulation stage displayed the most pronounced changes, as Ca2 + uptake and accumulation and Ca2 +-ATPase levels were the highest at this stage, likely involved in mineralization of the spicule. Biomarkers of Ca2 + metabolism may be good endpoints for potential future toxicity studies.