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Initiation of IP 3 ‐mediated Ca 2+ waves in Xenopus oocytes
Author(s) -
Marchant Jonathan,
Callamaras Nick,
Parker Ian
Publication year - 1999
Publication title -
the embo journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 7.484
H-Index - 392
eISSN - 1460-2075
pISSN - 0261-4189
DOI - 10.1093/emboj/18.19.5285
Subject(s) - xenopus , biology , receptor , biophysics , inositol trisphosphate receptor , inositol , inositol trisphosphate , inositol phosphate , microbiology and biotechnology , physics , biochemistry , gene
Inositol (1,4,5)‐trisphosphate (IP 3 ) evokes Ca 2+ liberation in Xenopus oocytes as elementary events (Ca 2+ puffs) that become coupled to propagate Ca 2+ waves with increasing [IP 3 ]. To investigate this transition between local and global Ca 2+ signaling, we developed an optical method for evoking rapid subcellular Ca 2+ elevations, while independently photoreleasing IP 3 and simultaneously recording confocal Ca 2+ images. Focal Ca 2+ elevations triggered waves within 100 ms of photoreleasing IP 3 , compared with latencies of seconds following photorelease of IP 3 alone. Wave velocity varied with [IP 3 ] but was independent of time after photorelease of IP 3 , indicating that delayed wave initiation did not involve slow binding of IP 3 to its receptors. The amount of Ca 2+ required to trigger a wave was ∼10‐fold greater than the average size of puffs, and puffs showed no progressive increase in magnitude before waves initiated. Instead, Ca 2+ puffs contributed to a slow rise in basal free [Ca 2+ ], which further increased puff frequency and sensitized IP 3 receptors so that individual events then triggered waves. Because the wave threshold is much greater than the size of the elementary puff, cells can employ both local and global signaling mechanisms, and the summation of stochastic behavior of elementary events allows generation of reproducible periodic waves.