In vivo and in vitro experiments demonstrated that the rectal caeca of the asteroid Asterias rubens selectively and actively excrete patent blue V (PBV) from the individual body cavity towards the gut lumen, a function already shown for another water-soluble dye (chlorophenol red, CPR) in several echinoderm species (including A. rubens). (These dyes are both known to be selectively and actively excreted by the vertebrate kidney.) Aquarium experiments were conducted in order to characterize in vivo CPR and PBV excretion kinetics in A. rubens. Dye eliminations were determined and were shown to be partly inhibited by para-aminohippuric acid (PAH), a competitive inhibitor of CPR transport in asteroid rectal caeca as well as in mammalian renal proximal tubules. The results show that the in vivo method is reliable and complements in vitro investigations. In particular, due to preservation of the organs’ integrity, the method preserves rectal caeca epithelium from rapid autolyse and allows the design of long-term experiments to study echinoderm excretion. |
