title: Two kinds of calcium-induced release of calcium from the sarcoplasmic reticulum of skinned cardiac cells.
abstract: This article compares the Ca(2+)-induced release of Ca2+ that is triggered by a rapid increase of free Ca2+ concentration at the outer surface of the sarcoplasmic reticulum of a skinned cardiac cell to the spontaneous release of Ca2+ that is produced by a steady-state high free Ca2+ concentration which overloads the sarcoplasmic reticulum with Ca2+ in a skinned cardiac cell. The first process, that is triggered by a rapid increase of free Ca2+ concentration at the outer surface of the sarcoplasmic reticulum, has a time- and Ca(2+)-dependent activation and inactivation, does not require any preload of the sarcoplasmic reticulum with Ca2+, and is not affected by the addition of inositol (1,4,5)-trisphosphate. The second process, i.e. the spontaneous release of Ca2+ from the sarcoplasmic reticulum, is not inactivated by a high free Ca2+ concentration, requires an overload of the sarcoplasmic reticulum with Ca2+ and is enhanced by inositol(1,4,5)-trisphosphate. The filling inside the sarcoplasmic reticulum with Ca2+ is critical for the triggering of the spontaneous release of Ca2+. On the other hand, the spontaneous release of Ca2+ has many similarities to the "Ca(2+)-induced release of Ca2+" that is observed for isolated sarcoplasmic reticulum vesicles incorporated into a lipid bilayer which is triggered by the increase of free Ca2+ concentration at the outer surface of the sarcoplasmic reticulum. Although the Ca(2+)-induced release of Ca2+ with time- and Ca(2+)-dependent activation and inactivation and the spontaneous release of Ca2+ are regulated by difference mechanisms, they are both inhibited by ryanodine, which suggests that they may take place through the same channel and may even have some partial common pathway.
authors.affiliation: Department of Physiology and Biophysics, Medical College of Virginia, Richmond 23298.
authors.forename: A
authors.initials: A
authors.lastname: Fabiato
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology*; D006321:Heart / Q000187:drug effects*; D006352:Heart Ventricles; D066298:In Vitro Techniques; D007700:Kinetics; D008954:Models, Biological; D009206:Myocardium / Q000378:metabolism*; D051381:Rats; D012519:Sarcoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism*
chemical_list: D002118:Calcium