BACKGROUND The endothelial (EC) surface layer (glycocalyx) has been shown to act as a barrier to transvascular exchange of solutes, and adhesion of leukocytes (WBCs) during the inflammatory process. It is a labile structure whose components are readily shed by the action of proteases and endoglycosidases. Details of shedding of specific constituents of the glycocalyx remain to be determined. OBJECTIVES To review the contributions of the primary glycosaminoglycans that comprise the glycocalyx, heparan sulfate (HS), chondroitin sulfate (CS) and hyaluronan (HA), as barrier to WBC-EC adhesion, and elucidate the rates of shedding of each component in response to an inflammatory stimulus. Assess the potential role that stiffness of the glycocalyx plays in resisting infiltration by WBCs during the adhesion process. METHODS Quantitate shedding of the glycocalyx in post-capillary venules of rat mesentery in response to superfusion of the tissue with 10-6 M fMLP. The presence and loss of HS, CS and HA was assessed by labeling all components with fluorescently labelled lectin (BS-1) or HS antibodies, and HA with fluorescently labelled hyaluronan binding protein (HBP). RESULTS Following a 30 min exposure of the mesentery to fMLP about 50% of HBP was lost in contrast to a previously shown loss of 20% of lectin labelled GAGs, and 25% loss of Mab labelled HS. The time constant for HBP shedding (5.8 min) was one-third that for BS-1 labelled GAGs (14.3 min). An attempt was made to assess stiffness of the glycocalyx by observing the motion of adhered lectin coated fluorescently labelled microspheres (FLM) under oscillatory flow conditions. Estimates of the elastic modulus of the glycocalyx revealed a value of 26 mPa, which was orders of magnitude below published data obtained by atomic force microscopy. CONCLUSIONS The relatively rapid shedding of HA compared to HS was consistent with the hypothesis that HA may form the dominant barrier to WBC-EC adhesion. Prior observations that HA lies closer to and parallel to the endothelial membrane, compared to HS suggests that the compact layer of HA near the EC membrane surrounds WBC adhesion receptors that are much shorter in length than the total thickness of the glycocalyx. The relatively low elastic modulus of the glycocalyx under shear is consistent with the hypothesis that the FLMs adhered to strands of HS normal to the EC surface that extended above the relatively more compact and stiffer HA layer below. Gradients of stiffness within the glycocalyx may not be detected by compressive indentation tests published to date.

中文翻译：

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炎症过程中糖胺聚糖从内皮糖萼的相对脱落及其对糖萼硬度的影响。

背景技术内皮（EC）表面层（糖胶）已被证明在炎性过程中充当溶质的跨血管交换和白细胞（WBC）粘附的屏障。它是一种不稳定的结构，其成分容易通过蛋白酶和糖苷内切酶的作用而脱落。糖萼的特定成分的脱落细节尚待确定。目的探讨构成糖萼，硫酸乙酰肝素（HS），硫酸软骨素（CS）和透明质酸（HA）的主要糖胺聚糖对WBC-EC粘附的阻碍作用，并阐明每种成分在反应中的脱落速率对炎性刺激。评估糖萼刚度在粘附过程中在抵抗WBC渗透方面可能发挥的作用。方法定量对大鼠肠系膜毛细血管后小静脉中糖萼的脱落，以响应组织与10-6 M fMLP的灌注。通过用荧光标记的凝集素（BS-1）或HS抗体标记所有组分，以及用荧光标记的透明质酸结合蛋白（HBP）标记HA，评估HS，CS和HA的存在与否。结果肠系膜暴露于fMLP 30分钟后，大约50％的HBP丢失，而先前显示的20％的凝集素标记的GAGs和25％的Mab标记HS丢失。HBP脱落的时间常数（5.8分钟）是BS-1标记的GAG的时间常数（14.3分钟）的三分之一。尝试通过观察振荡流动条件下粘附的凝集素包被的荧光标记微球（FLM）的运动来评估糖萼的刚度。糖萼的弹性模量估计值显示为26 mPa，比原子力显微镜获得的公开数据低几个数量级。结论与HS相比，HA脱落相对较快，这与HA可能构成WBC-EC粘附的主要障碍的假设相一致。与HS相比，先前观察到的HA与内皮膜更接近并平行，这表明HA在EC膜附近的致密层围绕着WBC粘附受体，其长度比糖萼总厚度短得多。糖萼在剪切作用下的相对较低的弹性模量与以下假设相一致：FLM附着在垂直于EC表面的HS链上，该HS链延伸到下面相对更紧密和更硬的HA层上方。