Tóm tắt
1. The mechanisms underlying inositol 1,4,5‐trisphosphate (InsP3)‐induced Ca2+ liberation were studied in Xenopus oocytes by using scanning and stationary‐point confocal fluorescence microscopy to record Ca2+ signals evoked by photorelease of InsP3 from a caged precursor. 2. Fluorescence measurements from confocal images showed that increasing [InsP3] evoked three distinct modes of Ca2+ liberation: a diffuse ‘pacemaker’ signal, localized transient puffs, and propagating waves. Peak free Ca2+ concentrations during waves and puffs (respectively, 2‐5 microM and 100‐200 nM) varied only slightly with [InsP3], whereas the pacemaker amplitude varied over a wider range (at least 1‐30 nM Ca2+). 3. The improved resolution provided by confocal point recording revealed discontinuous Ca2+ ‘blips’ during pacemaker release. These events were resolved only at particular locations and had time courses similar to the puffs (rise, approximately 50 ms; decay, a few hundred milliseconds) but with amplitudes one‐fifth or less of puff amplitudes. 4. We conclude that blips may arise through opening of single InsP3‐gated channels, whereas puffs reflect the concerted opening of several clustered channels due to local regenerative feedback by Ca2+.
