Water-soluble phosphodiesters (WSPDE) are a prominent feature of many 31P-NMR spectra; however, their role has remained somewhat of a mystery. What has been missed in almost all previous studies is the fact that two classes of WSPDE exist in vertebrates: those in mammals and those in the other (reptile-avian) line. The first is represented by glycerol phosphorylcholine and the second by serine ethanolamine phosphodiester. A further examination of the literature suggests a common role for all WSPDE as lysophospholipase inhibitors and therefore net sparers of phospholipids by decreasing phospholipid metabolic throughput.

Glycerol phosphorylcholine (GPC) and serine ethanolamine phosphodiester (SEP): evolutionary mirrored metabolites and their potential metabolic roles

This chapter documents the application of NMR spectroscopic methods to studies of the metabolism of cells and perfused organs. Progress in this area is attested to by the sheer number of publications. This area of research stands alone, as a means of shedding light on the metabolism and pharmacology of cells and organs, but also exists as a basis for the applications of NMR spectroscopic methods to in vivo and clinical situations. Methods of obtaining cellular extracts are included, but the bulk of the chapter is devoted to the methods that have been developed to obtain spectra from intact cells perfused in the NMR tube. Such methods as embedding in gels, use of microcarrier beads, hollow fibers, and spheroids are described and compared. Most of this work involves 31P-NMR, but some 13C-NMR tracer studies are also reported. A section is also devoted to the consideration of proton NMR as a means to monitor metabolism, and the necessity of not only suppressing the water signal, but also of removing all signals of extracellular origin, which has recently been accomplished. Finally some work on perfused organs is described and collated into a table that could prove useful for the reader. The question arises as to the relevance of the results with perfused organs relative to those in vivo. As clinical spectroscopy develops, future work must address this question.

NMR Studies of Metabolism of Cells and Perfused Organs

Publisher Summary This chapter focuses on nuclear magnetic resonance (NMR). These techniques are used for metabolic studies of cells and living tissues for several years. The NMR process can be described from either a classical or a quantum mechanical perspective. The classical approach is used for visualization of experiments and elucidation of challenges, particularly considering isolated spins. Quantum mechanical descriptions are necessary for detailed explanations in more complicated systems. The magnetism of some compounds (organic and inorganic), when they are placed in a strong magnetic field, arises from the magnetic moments of nuclei in the compound. Some of the observed parameters in NMR include chemical shift, spin coupling and spin decoupling, relaxation times, peak intensity, and spin echo. The ease in selecting analytical conditions to gain information from a wide range of endogenous metabolites and xenobiotics makes NMR a powerful technique. There are three possible approaches to cell studies—namely, cellular extraction, cellular suspensions, and perfusion of intact cells. Perfused intact cells may represent the best ex vivo approach to the noninvasive study of metabolism.

NMR and the study of pathological state in cells and tissues.

1. The effect of light and dark adaptation on the levels of phosphorus metabolites (nucleotide di- and triphosphates, phosphocreatine, pyridine nucleotide, inorganic phosphate, phosphodiesters, phosphomonoesters, and uridine diphosphate-glucose) in the toad (Bufo marinus) retina and retinal extracts was studied by 31P nuclear magnetic resonance (NMR) spectroscopy. 2. Spectra were acquired using an NMR probe specifically designed for superfusion and illumination of a single retina. Retinae were maintained at a steady state for up to 10 h in an electrolyte solution containing 10 mM Hepes buffer and bubbled with 98% O2-2% CO2, pH 7.8 at 20 degrees C. 3. The intracellular concentrations of the phosphorus metabolites were measured in total darkness or during prolonged exposure to light. The concentration of nucleoside triphosphates (NTP) in the dark-adapted retina was about 1.5 mM and that of phosphocreatine (PCr) was about 0.7 mM. 4. In saturating levels of light, 6.0 x 10(11) or 1.5 x 10(13) quanta s-1 cm-2 at 520 nm, the levels of PCr and phosphomonoesters rose, the levels of NTP and protons (pH) were maintained, and the levels of pyridine nucleotides and nucleotide diphosphates (NDP) fell. 5. A rise in the level of PCr in the presence of an unchanged level of NTP in the light-adapted retina indicates that the energy consumption of the retina is greater in the dark. 6. These results are in agreement with the results of oxygen consumption, glucose dependence, and electrophysiological studies which also indicate that the metabolic energy requirement of the retina decreases in light.

https://physoc.onlinelibrary.wiley.com/doi/pdf/10.1113/jphysiol.1993.sp019635

D.K. McFarlane

Papers

Phosphorus-31 nuclear magnetic resonance spectroscopy of toad retina.