Nuclear magnetic resonance measurement of cytosolic free calcium levels in human red blood cells.
Red blood cells were loaded with 1,2-bis(2-amino-5-fluorophenoxy)ethane-N,N,N',N'-tetraacetic acid (FBAPTA) by incubation with 50 microM of the acetoxymethyl ester (FBAPTA-AM), and cytosolic free Ca2+ was monitored with 19F-nuclear magnetic resonance (NMR). Loading with 50 microM FBAPTA-AM, which results in a final FBAPTA level of approximately 0.5 mM, caused only a 25-30% fall in cell ATP as measured by 31P-NMR when 5 mM pyruvate was present. Leakage of the NMR active Ca2+ indicator, which results from cell lysis, was corrected for with the addition of extracellular Eu3+ ions, extracellular ethyleneglycol-bis(beta-aminoethylether)-N,N'-tetraacetic acid (EGTA), or washing. With this method, we have found basal levels of cytosolic free Ca2+ averaging 61 +/- 6 nM (means +/- SE, n = 19). When the intracellular level of FBAPTA was varied from 0.1 to 1.0 mM, there was no correlation between the level of cytosolic free Ca2+ and the level of loading with FBAPTA. Addition of 10 microM of the Ca2+ ionophore A23187 with extracellular Ca2+ set at different levels by Ca2+-EGTA buffers caused an increase in cytosolic free Ca2+ as expected. Furthermore, ATP depletion caused a two- to three-fold increase in cytosolic free Ca2+, consistent with inhibition of Ca2+ efflux via that Ca2+-ATPase.
D000255:Adenosine Triphosphate / Q000097:blood; D002118:Calcium / Q000097:blood*; D003600:Cytosol / Q000378:metabolism; D004533:Egtazic Acid / Q000031:analogs & derivatives; D004912:Erythrocytes / Q000378:metabolism*; D006801:Humans; D009682:Magnetic Resonance Spectroscopy
D004533:Egtazic Acid; C039877:5,5'-difluoro-1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D000255:Adenosine Triphosphate; D002118:Calcium