Abstract
The behavior of the lithium (Li) ion in normal human erythrocytes has been studied by ^7^Li NMR. The uptake of Li into the cells was followed as a function of solution conditions, temperature, hematocrit, and blood age using dysprosium tripolyphosphate shift reagent. Under our conditions the uptake of Li increases with increasing hematocrit and blood age. For packed cells the extracellular ^7^Li spin‐lattice relaxation time was only slightly longer than the intracellular relaxation time. Thus, T~1~ may not be useful for separate observation of intra‐and extracellular Li in vivo. The intra‐ and extracellular T~2~s were substantially shorter than the corresponding T~1~s. Also, the intracellular T~2~ was considerably shorter than that for the extracellular compartment, suggesting that T~2~ may provide a noninvasive handle for observation of intracellular Li. Nuclear Overhauser enhancements could be observed for both extra‐and intracellular ^7^Li, confirming that dipolar coupling to ^1^H is a contributing relaxation mechanism. The ^7^Li NMR visibility was esentially 100% at high Li concentrations, decreasing to about 84% at 1 m__M__ Li. Based on time course studies of the invisibility, and a comparison of NMR and inductively coupled plasma results, it appears that the invisibility of the intra‐ and extracellular compartments for packed cells in the same. Although a ^23^Na double‐quantum signal could be observed for red blood cells, no double‐quantum signal was observed for ^7^Li. © 1991 Academic Press, Inc.