Using micro-colonies and isotope
kinetic measurements, we have shown that transport of ions (calcium, bicarbonate)
and organic elements which are part of the organic
matrix (aspartic acid), from sea water up to the calcification site,
is a rapid phenomenon (less than 2 min for ions, and 20 min for the complete
absorption of the amino acid, incorporated in proteins, exocytosed towards
the skeleton and incorporated in the mineral framework).
We also showed that calcium transit is paracellular from seawater to
the skeletogenic epithelium (calicoblastic) and there becomes transcellular,
implying the use of a calcium channel that has been cloned and sequenced.
The bicarbonate transport, however, seems to be aided by carbonic anhydrase.
The main source of skeletal carbon (70%) is metabolic CO2.
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