Ehrlich S, Wolff N, Schneiderman R, Maroudas A, Parker K H, Winlove C P
Department of Biomedical Engineering, Technion, Haifa, Israel.
Biorheology. 1998 Nov-Dec;35(6):383-97. doi: 10.1016/s0006-355x(99)80018-3.
We used equilibrium dialysis to measure the osmotic pressure of chondroitin sulphate (CS) solutions as a function of their concentration and fixed charge density (FCD) and the ionic strength and composition of the solution. Osmotic pressure varied nonlinearly with the concentration of chondroitin sulphate and in 0.15 M NaCl at FCDs typical of uncompressed cartilage (approximately 0.4 mmol/g extrafibrillar H2O) was approximately 3 atmospheres. Osmotic pressure fell by 60% as solution ionic strength increased up to about 1 M, but remained relatively constant at higher ionic strengths. The ratio of Ca2+ to Na+ in the medium was a minor determinant of osmotic pressure. The data are compared with a theoretical model of the electrostatic contribution to osmotic pressure calculated from the Poisson-Boltzmann equation using a rod-in-cell model for CS. The effective radius of the polyelectrolyte rod is taken as a free parameter. The model qualitatively reproduces the non-linear concentration dependence, but underestimates the osmotic pressure by an amount that is independent of ionic strength. This difference, presumably arising from oncotic and entropic effects, is approximately 1/3 of the total osmotic pressure at physiological polymer concentrations and ionic strength.
我们使用平衡透析法来测量硫酸软骨素（CS）溶液的渗透压，该渗透压是其浓度、固定电荷密度（FCD）以及溶液离子强度和组成的函数。渗透压随硫酸软骨素浓度呈非线性变化，在0.15M NaCl中，当FCD处于未压缩软骨的典型值（约0.4 mmol/g细胞外水）时，渗透压约为3个大气压。随着溶液离子强度增加至约1M，渗透压下降60%，但在更高离子强度下保持相对恒定。介质中Ca2+与Na+的比例对渗透压的影响较小。将这些数据与基于泊松-玻尔兹曼方程，使用CS的棒状细胞模型计算的渗透压静电贡献理论模型进行比较。聚电解质棒的有效半径作为一个自由参数。该模型定性地再现了非线性浓度依赖性，但低估了渗透压，且低估量与离子强度无关。这种差异可能源于胶体渗透压和熵效应，在生理聚合物浓度和离子强度下，约为总渗透压的1/3。
