Calcium transport across the isolated oral epithelium of scleractinian corals

Oral epithelia were isolated from Lobophyllia temprichii and Plerogyra sinuosa and placed in Ussing chambers. Calcium flux was measured under open circuit and short circuit conditions using ⁴⁵Ca. Only a small transepithelial potential of 1.5 mV was recorded under open circuit conditions and no effect on flux rates were observed when the preparation was short circuited. Unidirectional fluxes in single and paired experiments were consistently greater in the ectoderm to gastroderm direction than from gastroderm to ectoderm with net flux of Ca²⁺ frequently being more than 3x10^-4 Eq mm^-2 min^-1. A small number of paired experiments showed that net flux of Ca²⁺ was reduced by Sr²⁺ and sodium azide but not by dinitrophenol. Unidirectional fluxes from ectoderm to gastroderm appeared to have maxima in the early and late parts of the day when recorded between 0900 and 2100 hrs. It is concluded that active transport of Ca²⁺ occurs across the isolated oral epitheia and that this may be an initial step in the process of keletal Ca²⁺ deposition.