Fura-2 antagonises calcium-induced calcium release.
Calcium-induced calcium release (CICR) from the endoplasmic reticulum (ER) takes place through ryanodine receptors (RyRs) and it is often revealed by an increase of the cytosolic Ca(2+) concentration ([Ca(2+)](c)) induced by caffeine. Using fura-2-loaded cells, we find such an effect in bovine adrenal chromaffin cells, but not in cerebellar granule neurones or in HEK-293 cells. In contrast, a caffeine-induced [Ca(2+)](c) increase was clearly visible with either fluo-3 or cytosolic aequorin. Simultaneous loading with fura-2 prevented the [Ca(2+)](c) increase reported by the other Ca(2+) probes. Caffeine-induced Ca(2+) release was also measured by following changes of [Ca(2+)] inside the ER ([Ca(2+)](ER)) with ER-targeted aequorin in HEK-293 cells. Fura-2 loading did not modify Ca(2+) release from the ER. Thus, fura-2, but not fluo-3, antagonises the generation of the cytosolic Ca(2+) signal induced by activation of RyRs. Cytosolic Ca(2+) buffering and/or acceleration of Ca(2+) diffusion through the cytosol may contribute to these actions. Both effects may interfere with the generation of microdomains of high [Ca(2+)](c) near the ER release channels, which are essential for the propagation of the Ca(2+) wave through the cytosol. In any case, our results caution the use of fura-2 to study CICR.
Alonso
Maria Teresa
MT
Departamento de Fisiología y Bioquímica, Facultad de Medicina, Instituto de Biología y Genética Molecular, Universidad de Valladolid y Consejo Superior de Investigaciones Científicas, E-47005 Valladolid, Spain.
Chamero
Pablo
P
Villalobos
Carlos
C
García-Sancho
Javier
J
D000331:Aequorin / Q000494:pharmacology; D000814:Aniline Compounds / Q000494:pharmacology; D000818:Animals; D000831:Animals, Newborn; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000502:physiology*; D002417:Cattle; D002478:Cells, Cultured; D019439:Chromaffin Cells / Q000187:drug effects / Q000378:metabolism; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism*; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism*; D005057:Eukaryotic Cells / Q000187:drug effects / Q000378:metabolism*; D016257:Fura-2 / Q000494:pharmacology; D006801:Humans; D009474:Neurons / Q000187:drug effects / Q000378:metabolism; D017434:Protein Structure, Tertiary / Q000187:drug effects / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar; D019837:Ryanodine Receptor Calcium Release Channel / Q000187:drug effects / Q000378:metabolism; D014966:Xanthenes / Q000494:pharmacology
D000814:Aniline Compounds; D019837:Ryanodine Receptor Calcium Release Channel; D014966:Xanthenes; C059715:Fluo-3; D002110:Caffeine; D000331:Aequorin; D002118:Calcium; D016257:Fura-2