Ca2+ transients associated with openings of inositol trisphosphate-gated channels in Xenopus oocytes

J Physiol. 1996 Mar 15;491 ( Pt 3)(Pt 3):663-8. doi: 10.1113/jphysiol.1996.sp021247.


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+.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Calcium Channels / metabolism*
  • Cytophotometry
  • Inosine Triphosphate / physiology*
  • Ion Channel Gating / physiology*
  • Microscopy, Confocal
  • Oocytes / metabolism*
  • Xenopus laevis


  • Calcium Channels
  • Inosine Triphosphate