Role of free calcium and ATP in calcium release from cardiac sarcoplasmic reticulum fragments.
Using both isotopic and spectrophotometric techniques to monitor the overall Ca++ binding and release reactions, we have studied the effects of the relative free concentrations of Ca++, sarcoplasmic reticulum fragments (SRF) protein, and ATP on spontaneous Ca++ release by SRF isolated from normal canine hearts. Low free [Ca++] was achieved by using a Ca-EGTA buffer; higher (micromolar) values were obtained by direct Ca++ additions throughout the reactions. ATP concentrations were stabilized by an ATP-regenerating system or an ATP trap. Concentrations of nucleotides in the reaction mixtures were also determined. Release depended in part on the [Ca++]/[ATP] and on the [ATP]. Spontaneous Ca++ release was prevented or slowed when the [ATP] was rapidly lowered with the ATP trap. ATP regeneration delayed, but did not prevent Ca++ release. Ca++-induced Ca++ release was found in the presence of ADP and ATP. Verapamil and D 600 did not affect release. The results may provide a basis for the slowed Ca++ release in SRF from failing hearts.
D000244:Adenosine Diphosphate / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000378:metabolism* / Q000494:pharmacology; D000818:Animals; D001665:Binding Sites / Q000187:drug effects; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D002474:Cell-Free System; D004285:Dogs; D004305:Dose-Response Relationship, Drug; D007700:Kinetics; D009206:Myocardium / Q000378:metabolism*; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*
D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D002118:Calcium