Allbritton N L, Meyer T, Stryer L
Department of Cell Biology, Stanford University, CA 94305.
Science. 1992 Dec 11;258(5089):1812-5. doi: 10.1126/science.1465619.
The range of messenger action of a point source of Ca2+ or inositol 1,4,5-trisphosphate (IP3) was determined from measurements of their diffusion coefficients in a cytosolic extract from Xenopus laevis oocytes. The diffusion coefficient (D) of [3H]IP3 injected into an extract was 283 microns 2/s. D for Ca2+ increased from 13 to 65 microns 2/s when the free calcium concentration was raised from about 90 nM to 1 microM. The slow diffusion of Ca2+ in the physiologic concentration range results from its binding to slowly mobile or immobile buffers. The calculated effective ranges of free Ca2+ before it is buffered, buffered Ca2+, and IP3 determined from their diffusion coefficients and lifetimes were 0.1 micron, 5 microns, and 24 microns, respectively. Thus, for a transient point source of messenger in cells smaller than 20 microns, IP3 is a global messenger, whereas Ca2+ acts in restricted domains.
通过测量钙离子（Ca2+）或肌醇1,4,5-三磷酸（IP3）在非洲爪蟾卵母细胞胞质提取物中的扩散系数，确定了点源信使的作用范围。注入提取物中的[3H]IP3的扩散系数（D）为283平方微米/秒。当游离钙浓度从约90 nM升高到1 microM时，Ca2+的扩散系数从13平方微米/秒增加到65平方微米/秒。Ca2+在生理浓度范围内的缓慢扩散是由于其与缓慢移动或固定的缓冲剂结合。根据其扩散系数和寿命计算出的游离Ca2+在被缓冲之前、缓冲后的Ca2+以及IP3的有效作用范围分别为0.1微米、5微米和24微米。因此，对于直径小于20微米的细胞中的瞬时点源信使，IP3是一种全局信使，而Ca2+则在受限区域起作用。
