Abstract
The quantitation of intracellular sodium ion concentration [Na+]in perfused organs using NMR spectroscopy requires a knowledge of the extent of visibility of the 23Na resonance and of the intracellular volume of the organ. We have used a multinuclear NMR approach, in combination with the extracellular shift reagent dysprosium (III) tripolyphosphate, to determine the NMR visibility of intra- and extracellular 23Na and 35Cl ions, intracellular volume, and [Na+]in in the isolated Langendorff perfused rat heart. Based on a comparison of the extracellular volumes calculated using 2H and 23Na, 35Cl, or 59Co NMR of the perfused heart we conclude that resonances of extracellular sodium and chloride ions (including ions in interstitial spaces) are fully visible, contrary to assumptions in the literature. Furthermore, prolonged hypoxia or ischemia caused a dramatic increase in intracellular Na+ and [Na+] in rose to approach that in the external medium indicating full visibility of the intracellular 23Na resonance. Resonance intensities of intra- and extracellular 23Na ions, along with a knowledge of the extracellular space as a fraction of the total organ water space, yielded an average [Na+] in of about 10 mM (10 +/- 1.5 mM) for the rat heart at 37 degrees C. Double-quantum filtered 23Na NMR of the perfused rat heart in the absence and presence of paramagnetic reagents revealed, contrary to assumptions in the literature, that both intra- and extracellular sodium ions contribute to the detected signal.
Highlights
From the Departments of SPhysioloRy and Bio_phv-sics and SBwchemistry, Albert Einstein College of Medicine, Yeshiva University, Bronx; New Yo;k 10461
The quantitation of intracellular sodium ion concen- heart asa model system in a multinuclear(‘H, 23Na,35Cl,and tration [Na+li,in perfused organs using Nuclear magnetic resonance (NMR) spectros- 59C0)NMR study which includes the use of the extracellular copy requires a knowledge of the extent of visibility of reagents dysprosium [111] tripolyphosphate (Dy(PPPi)2)’(12)
Based on a comparison of the extracellular volumes calculated using ’H and 23Na,3sCl, or 69C0NMR of the perfused heart we conclude that resonances of extracellular soaway from the intracellular resonance [12] whilCeo3+ (K3Co(CN)6)serves solely as anextracellular marker sinceno NMR-detectable Go3+ is naturallypresentinmammalian tissues [18,19].It hasbeen previously shown that intracellular chloride is NMR invisible in human red blood cells [20], rat kidney tubules [4,21],and in theisolated perfused rat kidney [22] and the 35Cl NMR signal serves as an dium and chloride ions are fully visiblec,ontrary to assumptions in the used 23NaNMR, in combination with these approaches, to literature
Summary
From the Departments of SPhysioloRy and Bio_phv-sics and SBwchemistry, Albert Einstein College of Medicine, Yeshiva University, Bronx; New Yo;k 10461. We have used a multinuclear NMR ap- D Y ( P P P ~sh)i~fts the extracellular 23Naresonance upfield and proach, in combination with the extracellularshift reagent dysprosium [111] tripolyphosphate, to determine the NMR visibility of intra- and extracellular 23Naand 3sClions, intracellular volume, and [Na+Ii,in the isolated Langendorff perfused rat heart. Resonance intensities of intra- and extra- NMR are virtually the same This result confirms the comcellular 23Naions, along with a knowledge of the ex- plete visibility of extracellular sodium transitions and the tracellular space as a fraction of thetotal organ water space, yielded an average[Na+Iinof about 10 mM (10 f 1.5 mM) for the rat heart at 37°C. We have addressed the question of the visibility of intracellular sodium by performing 23NaNMR experiments under conditions where the intracellular sodium was increased by inducing hypoxia or ischemia. Nuclear magnetic resonance (NMR) offers a noninvasive and specific technique that permits repetitive measurements of intracellular Na’ concentra-
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