Increased gene expression of a facilitated diffusion urea transporter in the skin of the African lungfish (Protopterus annectens) during massively elevated post-terrestrialization urea excretion

Abstract

The full-length cDNA sequence of a putative urea transporter (IfUl) of the facilitated diffusion UT-A type has been cloned from the African lungfish Protopterus annectens. The IFUTcDNA is 1990bp in length and its open reading frame encodes a 409 amino acid long protein, with a calculated molecular mass of 44,723 Da. The sequence is closest to those of amphibians (∼65% amino acid homology), followed by mammals and elasmobranchs (∼60%), and then teleosts (∼50%). IfUT was clearly expressed in gill, kidney, liver, skeletal muscle and skin. Upon re-immersion in water after 33days of air exposure ('terrestrialization'), lungfish exhibited a massive rise in urea-N excretion which peaked at 12-30h with rates of 2000-5000μmol-N kg-1 h -1 (versus normal aquatic rates of