Abstract
Elasmobranch fishes rely on nitrogenous organic osmolytes to maintain body fluids slightly hyperosmotic to the surrounding seawater. Methylamines are an important part of this osmoregulatory strategy with trimethylamine oxide (TMAO) being a significant osmolyte. The skate (Leucoraja ocellata) lacks significant TMAO synthesis, relying on low whole animal losses (≤ 1.2 % day−1) to maintain TMAO during periods of food deprivation [Treberg and Driedzic, 2006, AJP 291: R1790‐R1798]. TMAO is accumulated intracellularly, creating a substantial concentration gradient (> 50 mM). Herein we revisit TMAO handling in skates and provide the first quantitative estimates of TMAO uptake in tissues based on the exchange of radiolabeled tracer between the plasma and tissue compartments. Muscle TMAO uptake is very low (0.6 μmol g−1 day−1), indicating a long residency time once compartmentalized within muscle cells. The uptake of TMAO differs greatly amongst tissues; visceral tissues (liver and intestine) having rates an order of magnitude greater than muscle. Assuming sodium‐dependent concentrating mechanism, similar to other osmolyte systems, accumulation of TMAO is likely a small fraction of overall metabolic rate, but could constitute a significant part of the osmoregulatory energetic demand in skates. Presentation funded by NSERC and CIHR.
Published Version
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