Department of Zoology, University of Oxford, South Parks Road, Oxford OX1 3PS, UK.
Tissue Cell. 1989;21(2):263-79. doi: 10.1016/0040-8166(89)90071-2.
Tardigrades weighed during desiccation in high or low humidities show a short period of rapid transpiration followed by an abrupt decline in transpiration which virtually arrests water loss. The amount of water retained following this 'permeability slump' is greater at low rates of desiccation but the slump is not a metabolic phenomenon, being reproducible in dead or narcotised animals. Tardigrades rinsed in hot chloroform (62 degrees C) for 5 hr still show the characteristic permeability decline when desiccated in 80% RH. However, 25hr rinsing in hot chloroform apparently obliterates the slump. Estimates of the bound water content of tardigrades by DSC show that this can account for the dehydrated masses of these chloroform-rinsed animals and that all free water is probably transpired. Lipid analysis of the 25 hr chloroform extracts by GC-MS reveals several lipid classes, predominantly free fatty acids (C(12)-C(18)); these are not detectable in the 5 hr extracts. Control rinsing in hot water has no apparent effect on the permeability slump. TEM tracer studies with lanthanum show the lipid-rich intracuticle to serve as a transpiration barrier in dehydrated animals but not in fully hydrated specimens. There is thus strong support for the role of intracuticular lipids in effecting the permeability slump. A model to explain this phenomenon on the basis of lipid phase changes is postulated.
在高湿度或低湿度下脱水时称重的缓步动物会经历短暂的快速蒸腾期，随后蒸腾速率急剧下降，几乎停止水分流失。在这种“渗透性崩溃”之后保留的水量在较低的干燥速率下更多，但崩溃不是代谢现象，在死亡或麻醉的动物中也可以重现。用热氯仿（62 摄氏度）冲洗 5 小时的缓步动物在 80% RH 中干燥时仍显示出特征性的渗透性下降。然而，25 小时的热氯仿冲洗显然消除了崩溃。DSC 对缓步动物结合水含量的估计表明，这可以解释经氯仿冲洗后的动物脱水质量，并且可能所有自由水都已蒸腾。GC-MS 对 25 小时氯仿提取物的脂质分析显示出几种脂质类，主要是游离脂肪酸（C(12)-C(18)）；这些在 5 小时提取物中不可检测。在热水中进行对照冲洗对渗透性崩溃没有明显影响。用镧进行的 TEM 示踪剂研究表明，富含脂质的内角质层在脱水动物中充当蒸腾屏障，但在完全水合的标本中则不然。因此，强烈支持内角质层脂质在产生渗透性崩溃中的作用。提出了一个基于脂质相变化的解释这种现象的模型。
