Two kinds of calcium-induced release of calcium from the sarcoplasmic reticulum of skinned cardiac cells.
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.
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Department of Physiology and Biophysics, Medical College of Virginia, Richmond 23298.
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*
D002118:Calcium