MU�OZ-GARCIA, Agust�*; RO, Jennifer; BROWN, Johnnie C.; WILLIAMS, Joseph B.; Ohio State University; Ohio State University; Applied Biosystems; Ohio State University: Sphingolipids in the stratum corneum and their relationship with cutaneous water loss in House sparrows, Passer domesticus, from arid and mesic environments

Lipids in the intercellular spaces in the vertebrate stratum corneum (SC), the outer layer of the epidermis, have been shown to be an important component in the formation and maintenance of the barrier to water vapor diffusion through the skin. Sphingolipids are one of the most important classes of lipids in the SC because they represent almost a half of the amount of the intercellular lipids. Their structural role in the SC is crucial to control of water loss through the skin. Two classes of sphingolipids have been found in the vertebrate SC, ceramides, characterized by a fatty acid bound to a sphingosine base, and cerebrosides, a ceramide with a hexose molecule ester-linked to the sphingosine. We measured cutaneous water loss (CWL) in two groups of House sparrows, Passer domesticus, one living in a desert environment, Taif, Saudi Arabia, and another living in a mesic environment, Ohio, USA. We found that CWL was lower in desert individuals. Thereafter, we analyzed the sphingolipids in the SC by reverse phase High Performance Liquid Chromatography (HPLC) and Atmospheric Pressure PhotoSpray ^TM Ionization (APPI) coupled with Mass Spectrometry (MS), a method that allowed us to identify and quantify each individual sphingolipid molecule in the SC. House sparrow populations showed qualitative and quantitative differences in their sphingolipid molecules. Moreover, desert sparrows had shorter carbon chains in the fatty acids of the sphingolipids, perhaps indicating a lower fluidity of the intercellular lipid structure, and exhibited less variability, both in the number of lipid classes and their quantities, than mesic birds.