Trimethylamine oxide transport across plasma membranes of elasmobranch erythrocytes

The aim of this study was to characterize the erythrocyte cell membrane tra nsport of trimethylamine oxide (TMAO) in the little skate, Raja erincea. Up take of TMAO occurs by two processes, Na+-dependent and Na+-independent. 2, 4 dinitrophenol (2,4 DNP), a known ATP synthesis inhibitor, inhibited TMAO uptake, suggesting the involvement of the Na+/K+-ATP pump in Na+-dependent TMAO transport. Na+-independent TMAO uptake was stimulated by cell swelling when erythrocytes were incubated in hypotonic elasmobranch incubation medi um. Swelling-activated, Na+-independent TMAO uptake was inhibited by the an ion transport inhibitors quinine and 4,4'-diisthiocyanostilbene-2,2'-dlisul fo acid (DIDS), two blockers of the swelling-activated osmolyte channel in skate erythrocytes. TMAO efflux was stimulated by hypotonic stress in the e rythrocytes of the spiny dogfish, Squalus acanthias. DIDS also inhibited th is efflux, indicating that TMAO is transported by the organic osmolyte chan nel in the erythrocytes of this elasmobranch as well. J. Exp. Zool. 284:605 -609, 1999. (C) 1999 Wiley-Liss, Inc.