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 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 greater than 1.5 microM 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 microM 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'-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.
Kirschenlohr
H L
HL
Department of Biochemistry, University of Cambridge, United Kingdom.
Metcalfe
J C
JC
Morris
P G
PG
Rodrigo
G C
GC
Smith
G A
GA
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D005289:Ferrets; D005461:Fluorine; D006321:Heart / Q000502:physiology*; D006863:Hydrogen-Ion Concentration; D008274:Magnesium / Q000378:metabolism*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D009206:Myocardium / Q000378:metabolism*; D010477:Perfusion
D005461:Fluorine; D008274:Magnesium; D002118:Calcium