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Ca2+ Transient, Mg2+, and pH Measurements in the Cardiac Cycle by 19F NMR

19F NMR indicators have been used to measure the free cytosolic cation concentrations ([Mn+]i, where M is the atomic symbol and n is the value of the charge) of Ca2+, H+, and Mg2+ in perfused ferret hearts. The [Ca2+]i transient, cytosolic pH (pHi), and [Mg2+]i have also been followed at 16 phases i...

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Bibliographic Details
Published in:Proceedings of the National Academy of Sciences - PNAS 1988-12, Vol.85 (23), p.9017-9021
Main Authors: Kirschenlohr, Heidi L., Metcalfe, James C., Morris, Peter G., Rodrigo, Glenn C., Smith, Gerry A.
Format: Article
Language:English
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Summary:19F NMR indicators have been used to measure the free cytosolic cation concentrations ([Mn+]i, where M is the atomic symbol and n is the value of the charge) of Ca2+, H+, and Mg2+ in perfused ferret hearts. The [Ca2+]i transient, cytosolic pH (pHi), and [Mg2+]i have also been followed at 16 phases in the cardiac cycle in hearts paced at 1.25 Hz at 30 degrees C. The initial [Ca2+]i rose rapidly after a 50-ms delay, was maximal at >1.5 μ M after 150 ms, and declined thereafter to the initial concentration. In contrast, no significant changes in pHi (pH 7.03 ± 0.08) or [Mg2+]i (1.2 ± 0.1 mM) were detected in the cycle. A decrease in developed pressure when the [Ca2+]i indicator (but not the pHi or [Mg2+]i indicator) was loaded into hearts was substantially reversed by the addition of 50 μ M ZnCl2 to the perfusion medium. The Zn2+ was taken up into the myoplasm and displaced Ca2+ bound to the indicator, a symmetrically substituted difluoro derivative of 1,2-bis(o-aminophenoxy)ethane-N,N,N′,N$^{\p rime}$-tetraacetic acid (5FBAPTA), as evidenced by the appearance of the Zn-5FBAPTA resonance. The decrease in developed pressure caused by 5FBAPTA, therefore, may be due to its Ca2+ buffering effect on the myoplasm. By coloading hearts with the [Ca2+]i and pHi indicators, simultaneous measurement of several [Mn+]i was demonstrated, which should provide a useful addition to the methods available to monitor cardiac function and pharmacology.
ISSN:0027-8424
1091-6490
DOI:10.1073/pnas.85.23.9017