title: Reverse mode of the sarcoplasmic reticulum calcium pump and load-dependent cytosolic calcium decline in voltage-clamped cardiac ventricular myocytes.
abstract: We have characterized [Ca](i) decline in voltage-clamped rabbit ventricular myocytes with progressive increases in sarcoplasmic reticulum (SR) calcium load. "Backflux" through the SR calcium pump is a critical feature which allows realistically small values for SR calcium leak fluxes to be used. Total cytosolic calcium was calculated from the latter part of [Ca](i) decline using rate constants for cellular calcium buffers. Intra-SR calcium buffering characteristics were also deduced. We found that the net SR calcium pump flux and rate of [Ca](i) decline decreased as the SR free [Ca] rose, with pump parameters held constant. We have therefore characterized for the first time in intact myocytes both forward and reverse SR calcium pump kinetics as well as intra-SR calcium buffering and SR calcium leak. We conclude that the reverse flux through the SR calcium pump is an important factor in comprehensive understanding of dynamic SR calcium fluxes.
authors.affiliation: Department of Physiology, Loyola University Chicago, Maywood, Illinois, 60153, USA.
authors.forename: T R
authors.initials: TR
authors.lastname: Shannon
authors.forename: K S
authors.initials: KS
authors.lastname: Ginsburg
authors.forename: D M
authors.initials: DM
authors.lastname: Bers
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D002478:Cells, Cultured; D003600:Cytosol / Q000378:metabolism; D006321:Heart / Q000502:physiology*; D006352:Heart Ventricles; D007425:Intracellular Membranes / Q000502:physiology / Q000648:ultrastructure; D007700:Kinetics; D009206:Myocardium / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D011817:Rabbits; D012519:Sarcoplasmic Reticulum / Q000201:enzymology* / Q000648:ultrastructure; D014336:Troponin / Q000378:metabolism
chemical_list: D014336:Troponin; D000252:Calcium-Transporting ATPases; D002118:Calcium