Localized all-or-none calcium liberation by inositol trisphosphate.
Laser confocal microscopy was used to monitor calcium ion (Ca2+) liberation from highly localized (micrometer) regions of intact Xenopus oocytes in response to photo-released inositol 1,4,5-trisphosphate (InsP3). Local Ca2+ release varied in an all-or-none manner with increasing amount of InsP3, in contrast to signals recorded from larger areas, which grew progressively as the concentration of InsP3 was raised above a threshold. Liberation of Ca2+ was restricted to within a few microns of the site of InsP3 release and, in response to agonist activation, localized regions of the oocyte showed asynchronous oscillations in cytoplasmic Ca2+ release. Results obtained with this technique provided direct evidence that InsP3-induced Ca2+ liberation was quantized and suggest that the InsP3-sensitive Ca2+ pool may be a collection of independent, localized compartments that release Ca2+ in an all-or-none manner.
Parker
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I
Department of Psychobiology, University of California, Irvine 92717.
Ivorra
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I
D000818:Animals; D002118:Calcium / Q000502:physiology*; D004305:Dose-Response Relationship, Drug; D015544:Inositol 1,4,5-Trisphosphate / Q000494:pharmacology*; D007425:Intracellular Membranes / Q000187:drug effects; D008027:Light; D009865:Oocytes / Q000187:drug effects; D014982:Xenopus laevis
D015544:Inositol 1,4,5-Trisphosphate; D002118:Calcium