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Role of cytosolic Ca2+ in inhibition of InsP3‐evoked Ca2+ release in Xenopus oocytes.
Author(s) -
Ilyin V,
Parker I
Publication year - 1994
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.1994.sp020211
Subject(s) - cytosol , liberation , xenopus , inositol , biophysics , calcium , intracellular , chemistry , conditioning , inositol trisphosphate , endocrinology , medicine , biology , biochemistry , in vitro , receptor , enzyme , gene , statistics , mathematics
1. Calcium liberation induced in Xenopus oocytes by flash photorelease of inositol 1,4,5‐trisphosphate (InsP3) from a caged precursor was monitored by confocal microfluorimetry. The object was to determine whether inhibition of Ca2+ release seen with paired flashes arose as a direct consequence of elevated cytosolic free [Ca2+]. 2. Responses evoked by just‐suprathreshold test flashes were not inhibited by subthreshold conditioning flashes, but were strongly suppressed when conditioning flashes were raised above threshold. 3. Inhibition at first increased progressively as the inter‐flash interval was lengthened to about 2 s and thereafter declined, with a half‐recovery at about 4 s. 4. Intracellular injections of Ca2+ caused relatively slight inhibition of InsP3‐evoked signals, even when cytosolic free [Ca2+] was elevated to levels similar to those at which strong inhibition was seen in paired‐flash experiments. 5. Recovery from inhibition was not appreciably slowed when Ca2+ was injected to raise the free Ca2+ level between paired flashes. 6. We conclude that inhibition of InsP3‐evoked Ca2+ liberation is not directly proportional to cytosolic free Ca2+ level and that recovery from inhibition in paired‐pulse experiments involves factors other than the decline of cytosolic [Ca2+] following a conditioning response.