Sha'afi R I, Rich G T, Mikulecky D C, Solomon A K
J Gen Physiol. 1970 Apr;55(4):427-50. doi: 10.1085/jgp.55.4.427.
A new method has been developed for measuring the permeability coefficient, omega, of small nonelectrolytes. The method depends upon a mathematical analysis of the time course of cell volume changes in the neighborhood of the minimum volume following addition of a permeating solute to an isosmolal buffer. Coefficients determined by the minimum volume method agree with those obtained using radioactive tracers. omega for urea in human red cells was found to decrease as the volume flow, J(v), into the cell increased. Such behavior is entirely unexpected for a single uniform rate-limiting barrier on the basis of the linear phenomenological equations derived from irreversible thermodynamics. However, the present findings are consonant with a complex membrane system consisting of a tight barrier on the outer face of the human red cell membrane and a somewhat less restrictive barrier behind it closer to the inner membrane face. A theoretical analysis of such a series model has been made which makes predictions consistent with the experimental findings.
已经开发出一种测量小的非电解质渗透系数ω的新方法。该方法依赖于对在等渗缓冲液中加入渗透溶质后，细胞体积在最小体积附近变化的时间过程进行数学分析。通过最小体积法测定的系数与使用放射性示踪剂获得的系数一致。发现人红细胞中尿素的ω随着流入细胞的体积流量J(v)增加而降低。基于不可逆热力学推导的线性唯象方程，对于单一均匀的限速屏障而言，这种行为是完全出乎意料的。然而，目前的研究结果与一个复杂的膜系统相符，该系统由人红细胞膜外表面的紧密屏障和靠近内膜面的稍宽松的屏障组成。已经对这样一个串联模型进行了理论分析，其预测结果与实验结果一致。
