Range of Messenger Action of Calcium Ion and Inositol 1,4,5-Trisphosphate

Publisher Website
Google Scholar
Abstract
The range of messenger action of a point source of Ca 2+ or inositol 1,4,5-trisphosphate (IP 3 ) was determined from measurements of their diffusion coefficients in a cytosolic extract from Xenopus laevis oocytes. The diffusion coefficient ( D ) of [ 3 H]IP 3 injected into an extract was 283 μm 2 /s. D for Ca 2+ increased from 13 to 65 μm 2 /s when the free calcium concentration was raised from about 90 nM to 1 μm. The slow diffusion of Ca 2+ in the physiologic concentration range results from its binding to slowly mobile or immobile buffers. The calculated effective ranges of free Ca 2+ before it is buffered, buffered Ca 2+ , and IP 3 determined from their diffusion coefficients and lifetimes were 0.1 μm, 5 μm, and 24 μm, respectively. Thus, for a transient point source of messenger in cells smaller than 20 μm, IP 3 is a global messenger, whereas Ca 2+ acts in restricted domains.