Elevated levels of trimethylamine oxide in muscles of deep-sea gadiform teleosts: A high-pressure adaptation?

Abstract

Trimethylamine oxide (TMAO) as an osmolyte typically occurs at 20–70 mM in shallow-water marine teleost fishes. However, it has not been previously examined in deep-living species. We collected species from two families of benthic gadiform teleosts by otter trawl from the continental slope (1,800–2,000 m) and abyssal plain (2,850 m) off the Oregon coast. Muscle and plasma samples were analyzed for TMAO with a picric acid method. Muscle contents (below in millimoles/kilogram of wet weight) were found to be higher than previously reported for teleosts. Results from Macrouridae from 1,800–2,200 m were as follows: Albatrossia pectoralis, 83 ± 10; Coryphaenoides cinerus, 121 ± 11. Results from Macrouridae from 2,850 m were significantly higher: C. leptolepis, 158 ± 20; C. fillifer, 177 ± 8; C. armatus, 173 ± 5. Caught at both depths, Antimora microlepis (Moridae) had 211 ± 14. Plasmas had low TMAO (2–15 mM) and high Na+concentrations (227–273 mM), except A. microlepis plasma, which had the lowest Na+ (219 ± 30 mM) and highest TMAO (159 ± 46 mM). Osmotic pressures of fresh plasma (423–557 mosm) correlated highly with muscle TMAO and with plasma TMAO plus Na+ levels. These higher osmolalities may reduce osmoregulatory costs. However, as a methylamine known to stabilize protein, TMAO may counteract destabilizing effects of hydrostatic pressure on cellular proteins. With purified C. leptolepis muscle lactate dehydrogenase, 250 mM TMAO fully offset a 30% increase in NADH Km induced by 300 atm. J. Exp. Zool. 279:386–391, 1997. © 1997 Wiley-Liss, Inc.