title: Ca2+ uptake by cardiac sarcoplasmic reticulum ATPase in situ strongly depends on bound creatine kinase.
abstract: The role of creatine kinase (CK) bound to sarcoplasmic reticulum (SR), in the energy supply of SR ATPase in situ, was studied in saponin-permeabilised rat ventricular fibres by loading SR at pCa 6. 5 for different times and under different energy supply conditions. Release of Ca2+ was induced by 5 mM caffeine and the peak of relative tension (T/Tmax) and the area under isometric tension curves, ST, were measured. Taking advantage of close localisation of myofibrils and SR, free [Ca2+] in the fibres during the release was estimated using steady state [Ca2+]/tension relationship. Peak [Ca2+] and integral of free Ca2+ transients (S[Ca2+]f) were then calculated. At all times, loading with 0.25 mM adenosine diphosphate, Mg2+ salt (MgADP) and 12 mM phosphocreatine (PCr) [when adenosine triphosphate (ATP) was generated via bound CK] was as efficient as loading with both 3.16 mM MgATP and 12 mM PCr (control conditions). However, when loading was supported by MgATP alone (3.16 mM), T/Tmax was only 40% and S[Ca2+]f 31% of control (P < 0.001). Under these conditions, addition of a soluble ATP-regenerating system (pyruvate kinase and phosphoenolpyruvate), did not increase loading substantially. Both ST and S[Ca2+]f were more sensitive to the loading conditions than T/Tmax and peak [Ca2+]. The data suggest that Ca2+ uptake by the SR in situ depends on local ATP/ADP ratio which is effectively controlled by bound CK.
authors.affiliation: Laboratoire de Cardiologie Cellulaire et Moléculaire, INSERM U-446, Faculté de Pharmacie Université Paris-Sud, 5 rue Jean-Baptiste Clément, F-92296, Châtenay-Malabry, Cedex, France.
authors.forename: A
authors.initials: A
authors.lastname: Minajeva
authors.forename: R
authors.initials: R
authors.lastname: Ventura-Clapier
authors.forename: V
authors.initials: V
authors.lastname: Veksler
mesh_terms: D000244:Adenosine Diphosphate / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D003402:Creatine Kinase / Q000378:metabolism*; D007537:Isometric Contraction; D008297:Male; D009200:Myocardial Contraction; D009206:Myocardium / Q000201:enzymology* / Q000648:ultrastructure; D010725:Phosphocreatine / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D012519:Sarcoplasmic Reticulum / Q000201:enzymology*
chemical_list: D010725:Phosphocreatine; D002110:Caffeine; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D003402:Creatine Kinase; D000252:Calcium-Transporting ATPases; D002118:Calcium