Department of Biology, University of Southern Indiana, Science Center 1255 8600 University Blvd, Evansville, IN 47712, USA
Department of Biology, University of Southern Indiana, Science Center 1255 8600 University Blvd, Evansville, IN 47712, USA.
J Exp Biol. 2018 Jun 7;221(Pt 11):jeb176438. doi: 10.1242/jeb.176438.
To survive high temperatures in a terrestrial environment, animals must effectively balance evaporative heat loss and water conservation. In passerine birds, cutaneous water loss (CWL) is the primary avenue of water loss at thermoneutral temperatures and increases slightly as ambient temperature increases, indicating a change in the permeability of the skin. In the stratum corneum (SC), the outermost layer of the skin, lipids arranged in layers called lamellae serve as the primary barrier to CWL in birds. The permeability of these lamellae depends in large part on the ability of lipid molecules to pack closely together in an ordered orthorhombic phase state. However, as temperature increases, lipids of the SC become more disordered, and may pack in more permeable hexagonal or liquid crystalline phase states. In this study, we used Fourier transform infrared spectroscopy to monitor the phase state of lipids in the SC of house sparrows () at skin temperatures ranging from 25 to 50°C. As temperature increased, lipids became slightly more disordered, but remained predominantly in the orthorhombic phase, consistent with the small increase in CWL observed in house sparrows as ambient temperature increases. These results differ considerably from studies on mammalian SC, which find a predominantly hexagonal arrangement of lipids at temperatures above 37°C, and the increased order in avian SC may be explained by longer lipid chain length, scarcity of cholesterol and the presence of cerebrosides. Our results lend further insight into the arrangement and packing of individual lipid molecules in avian SC.
为了在陆地环境中耐受高温，动物必须有效地平衡蒸发散热和水分保持。在雀形目鸟类中，皮肤水分流失（CWL）是在热中性温度下水分流失的主要途径，随着环境温度的升高而略有增加，表明皮肤的通透性发生了变化。在皮肤的最外层角质层（SC）中，排列成层状的脂质称为薄片，是鸟类 CWL 的主要屏障。这些薄片的通透性在很大程度上取决于脂质分子紧密排列在有序正交相状态的能力。然而，随着温度的升高，SC 中的脂质变得更加无序，并且可能以更具渗透性的六角形或液晶相状态包装。在这项研究中，我们使用傅里叶变换红外光谱法监测从 25°C 到 50°C 的皮肤温度下家麻雀（）SC 中脂质的相态。随着温度的升高，脂质变得稍微无序，但仍主要处于正交相，与家麻雀随环境温度升高而观察到的 CWL 小幅度增加一致。这些结果与哺乳动物 SC 的研究有很大不同，在 37°C 以上的温度下发现脂质主要呈六角形排列，而鸟类 SC 中增加的有序性可能是由于脂质链长较长、胆固醇缺乏和神经酰胺的存在。我们的研究结果进一步深入了解了鸟类 SC 中单个脂质分子的排列和包装。
