| Summary: | Living cells are often exposed to dramatic changes in environmental conditions and adapt to these changes by expression of inducible enzyme or signal transduction pathways that provide an appropriate response to the environmental signals. In marine mammals, these extreme changes in environment (a stress stimulus) may be induced by deep or prolonged diving. However, the physiological systems activated by stress stimuli often not only protect the cell but may also prove damaging. This dual pathway is evident in the sphingolipids, ceramides and sphinosine‐1‐phosphate (S‐1‐P), which are known to harm (apoptosis) and protect cells (from oxidative stress), respectively. Regulation of these seemingly contradictory functions must operate on multiple pathways to ensure an adequate homeostasis. Therefore, the ratio of ceramides to sphingosine‐1‐phosphates, in particular, may be a useful prediction of stress at the cellular level. Sphingolipids in marine mammal tissue have never before been characterized; therefore, it was our goal to establish ratios of ceramides to S‐1‐P in several species of diving mammals. We analyzed muscle tissue from 5 species of marine mammals ( Pusa hispida, Phoca largha, Callorhinus ursinus, Eumetopia jubatus, and Odobenus rosmarus ) as well as a control ( Mus musculus ) and found significantly different ratios of ceramides to S‐1‐P in marine mammals correlating with diving capacity. These differences may indicate that increased oxidative stress endured by cell membranes necessitate increased S‐1‐P as a protective mechanism. Additionally, marine mammals typically donˈt suffer from the metabolic diseases often associated with increased ceramide production, lowering the ceramide:S‐1‐P ratio that much further. This first comparative account of sphingolipid ratios in marine mammals may link levels of oxidative stress to dive depth and duration, an important environmental variable in the life history of all marine mammals.
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