Kalia Y N, Pirot F, Guy R H
Department of Biopharmaceutical Sciences, University of California-San Francisco 94143-0446, USA.
Biophys J. 1996 Nov;71(5):2692-700. doi: 10.1016/S0006-3495(96)79460-2.
The objective of this study was to determine whether a structurally heterogeneous biomembrane, human stratum corneum (SC), behaved as a homogeneous barrier to water transport. The question is relevant because the principal function of the SC in vivo is to provide a barrier to the insensible loss of tissue water across the skin. Impedance spectra (IS) of the skin and measurements of the rate of transepidermal water loss (TEWL) were recorded sequentially in vivo in human subjects as layers of the SC were progressively removed by the serial application of adhesive tape strips. The low-frequency (< or = 100 rad s-1) impedance of skin was much more significantly affected by tape stripping than the higher frequency values; removal of the outermost SC layer had the largest effect. In contrast, TEWL changed little as the outer SC layers were stripped off, but increased dramatically when 6-8 microns of the tissue had been removed. It follows that the two noninvasive techniques probe SC barrier integrity in somewhat different ways. After SC removal, recovery of barrier function, as assessed by increasing values of the low-frequency impedance, apparently proceeded faster than TEWL decreased to the prestripping control. The variation of TEWL as a function of SC removal behaved in a manner entirely consistent with a homogeneous barrier, thereby permitting the apparent SC diffusivity of water to be found. Skin impedance (low frequency) was correlated with the relative concentration of water within the SC, thus providing an in vivo probe for skin hydration. Finally, the SC permeability coefficient to water, as a function of SC thickness, was calculated and correlated with the corresponding values of skin admittance derived from IS.
本研究的目的是确定一种结构异质的生物膜——人类角质层（SC）——是否表现为对水运输的均质屏障。这个问题很重要，因为SC在体内的主要功能是为组织水分通过皮肤的无感流失提供屏障。在人类受试者体内，随着通过连续粘贴胶带条逐渐去除SC各层，依次记录皮肤的阻抗谱（IS）和经表皮水分流失率（TEWL）的测量值。皮肤的低频（≤100 rad s-1）阻抗比高频值受胶带剥离的影响要大得多；去除最外层的SC层影响最大。相比之下，当剥离外层SC层时，TEWL变化很小，但当去除6 - 8微米组织时，TEWL会急剧增加。由此可见，这两种非侵入性技术以 somewhat 不同的方式探测SC屏障的完整性。去除SC后，通过低频阻抗值增加来评估的屏障功能恢复，显然比TEWL降至剥离前对照时的速度要快。TEWL随SC去除的变化表现与均质屏障完全一致，从而可以求出水在SC中的表观扩散率。皮肤阻抗（低频）与SC内水的相对浓度相关，因此为皮肤水合作用提供了一种体内探测方法。最后，计算了SC对水的渗透系数作为SC厚度的函数，并将其与从IS得出的皮肤导纳的相应值相关联。
