AJP - Heart and Circulatory Physiology, Vol 252, Issue 6 1138-H1146, Copyright © 1987 by American Physiological Society

ARTICLES

Nuclear magnetic resonance studies of intracellular ions in perfused frog heart

D. Burstein and E. T. Fossel

Intracellular sodium, potassium, and lithium were observed in a perfused frog heart by nuclear magnetic resonance (NMR) spectroscopy. A perfusate buffer containing the shift reagent, dysprosium tripolyphosphate, was used in combination with mathematical filtering or presaturation of the extracellular resonance to separate the intra- and extracellular sodium NMR signals. Addition of 10 microM ouabain to the perfusate, perfusion with a zero potassium, low-calcium buffer, and replacement of 66% of the perfusate sodium with lithium resulted in the following percent changes in the intracellular sodium levels (mean +/- SD): ouabain + 460 +/- 60% (n = 6), zero potassium + 300 +/- 30% (n = 3), and lithium - 51 +/- 6% (n = 3). An increase of 45% in the intracellular sodium was observed when changing the pacing rate from 0 to 60 beats/min (with proportional changes for intermediate pacing rates). The ratio of intracellular potassium to sodium concentration was determined to be 2.3 by NMR, indicating that a substantial amount of the intracellular potassium is undetectable with these NMR methods. In addition, intracellular lithium was observed during perfusion with a lithium-containing perfusate.

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