Gerald B. Matson

Spatial localization of tissue metabolites by phosphorus-31 NMR rotating-frame zeugmatography

Abstract Surface coils are employed for rotating-frame zeugmatography experiments to accomplish one-dimensional 31 P metabolite mapping in phantoms and bovine eyes. The spatially dependent β 1 field of the surface coil provides the necessary magnetic field gradient, and the experiments are designed to acquire 15–32 spectra obtained with rf pulses of equally incremented durations. Regions of the sample are distinguished on the basis of the differing magnetization precessional rates about the spatially dependent β 1 field. Thus the mapping dimension corresponds to changes in the transverse ( x′y′ ) magnetization components of the β 1 field, which correspond to successive curved surfaces of constant β 1 field strength. Two-dimensional Fourier transform processing of the data results in a metabolite map composed of a suite of spectra displayed as a function of the mapping dimension. Experiments with bovine eye phantoms reveal that T 1 discrimination can produce a loss of resolution due to smearing in the mapping dimension. Resonance offset effects are also apparent at distances removed from the coil. Elimination of the T 1 discrimination-induced smearing is demonstrated through the incorporation of a saturation pulse into the experiment. Application of the method to the intact bovine eye is shown to result in metabolite maps delineating contributions from constituent ocular tissues of the bovine eye.

Intracellular pH and the metabolic status of dormant and developing Artemia embryos

Abstract Encysted embryos of the brine shrimp Artemia salina have long been known to enter profound dormancy under anaerobic conditions. Utilizing in vivo 31 P nuclear magnetic resonance, we show that the reversible transitions between anaerobic dormancy and aerobic development are accompanied by large (>1 unit) intracellular pH changes, the more acid pH being associated with the dormant state. Furthermore, dormant cyst intracellular pH is independent of that of the buffer, suggesting the potential for pH-mediated regulation of enzyme activities during dormancy. An example concerning cyst nucleotide metabolism is discussed.

A modified rotating frame experiment based on a fourier series window function. Application to in vivo spatially localized NMR spectroscopy

A fourier series window approach to the rotating frame experiment is employed in conjunction with surface coils to accomplish one-dimensional spatial localization of phosphorus-containing metabolites in phantoms and the in vivo rat brain. The rotating frame experiment delineates sample regions on the basis of a B1 field gradient across the sample which for the experiments described in this paper are provided by a surface coil. In the usual rotating frame experiment, a suite of spectra (termed a metabolite map) is obtained by incrementing the evolution pulse duration with the spectra displayed as a function of the nutational frequency about the B1 field. The total time of the experiment depends on the desired degree of spatial resolution, and substantial time savings can be obtained when the desired result is spectral information from a single or a few selected regions (slices). The approach taken here is to utilize a Fourier series window function representation of the nutational frequencies over the region of interest. This procedure allows convenient selection of the localized region, thus avoiding Fourier transformation in the second (mapping) dimension. For the case of a single region of interest, the spectral parameters can be adjusted to maximize the number of data files in which the evolution pulse nutates the magnetizations at the center of the slice through a multiple of 180°. Data files not contributing significant signal to a selected slice can be omitted to further minimize the experimental accumulation time.

31P-NMR study of the activation of the sea urchin egg☆

Abstract 31 P-NMR has been used as a non-invasive probe to examine changes in pH and phosphate metabolism at fertilization of the sea urchin egg. A pH increase of 0.43 units was measured following fertilization. This value is in good agreement with measurements made with pH micro-electrodes and the DMO method, but is contrasted with the failure of other workers to measure a pH increase with 31 P-NMR. Significantly the increase in arginine phosphate associated with fertilization was found not to be triggered by a pH increase induced by NH 4 C1 activation. In addition we examined the 31 P-NMR spectrum of sea urchin sperm and determined their intracellular pH.

Longitudinal (T1) relaxation times of phosphorus metabolites in the bovine and rabbit lens

Longitudinal (T1) magnetic relaxation times for the major phosphorus-containing metabolites present in the bovine and rabbit lens under organ culture conditions and in the bovine and rabbit globe have been determined. Significant differences in T1 for the major phosphorus metabolites in each case are observed, as well as for the same metabolite in the two species examined. Species-dependent lens hydration may account, in part, for these differences. Because of the requirement for rapid repetitive pulsing for the attainment of optimum signal collection efficiency by the Fourier transform nuclear magnetic resonance method, significant differential saturation of metabolite resonance intensities occurs in circumstances where appreciable differences in T1 relaxation times are present, which, unless corrected, leads to erroneous determinations of relative metabolite levels. The net effect of assessing relative metabolite levels in terms of the percentage of total phosphate signal, without a correction for T1 discrimination, is to underestimate metabolites with a long T1 (sugar phosphates) and overestimate those metabolites with a short T1 (ATP). Individual metabolite T1 discrimination factors are calculated from integrated areas of spectra acquired using short and long repetition times as well as from metabolite T1 values. They are then employed, for the first time, for the correction of 31P-NMR spectra of bovine and rabbit lenses. Corrected spectra provide relative metabolite levels for lenticular ATP which are in excellent agreement with values determined by chemical and enzymatic assays.

Measurement of longitudinal relaxation times using surface coils

Abstract The poor B 1 field homogeneity associated with surface coils reduces the effectiveness of inversion-recovery techniques for determination of T 1 relaxation times. This paper presents a variation of the saturation-recovery T 1 experiment which introduces periodic phase shifts in the saturating irradiation to achieve rapid and effective saturation of the sample magnetization, thereby avoiding the complications of B 1 field inhomogeneity. Comparison of the presented technique with the inversion-recovery technique utilizing a composite inverting pulse and alternating phase acquisition is provided. A discussion of the relative merits of each technique is presented.

Conformational kinetics of methyl nitrite. I. NMR spectral evidence for statistical intramolecular vibrational redistribution

Pressure dependent rate constants for syn⇄anti conformational exchange in gaseous methyl nitrite and in gaseous methyl nitrite–CO2 mixtures have been obtained from line shape analyses of 1H NMR spectra. The pressure dependence of the exchange rates is consistent with a specific reaction rate constant of ∼1×109/s which agrees with RRKM calculations demonstrating that intramolecular vibrational redistribution is occurring at the statistical limit in methyl nitrite molecules with ∼12 kcal/mol of internal vibrational energy. At 12 kcal/mol methyl nitrite has a state density of ∼160/cm−1. These results indicate strong anharmonic and/or Coriolis coupling between vibrational levels. Bimolecular rate data for methyl nitrite and methyl nitrite–CO2 mixtures are consistent with a collisional efficiency βp for CO2 of 0.95(8) for activation of syn–anti conformational exchange at 258.8 K.

Surface coil phosphorus-31 nuclear magnetic resonance studies of the intact eye

The feasibility of employing the surface coil probe technique for the non-invasive study of ocular tissue metabolism by phosphorus-31 nuclear magnetic resonance spectroscopy (31P NMR) in enucleated bovine, rabbit, human and rat globes is demonstrated. An assessment of individual phosphorus-metabolite contributions from ocular tissues, including the cornea, lens and iris, to the overall 31P NMR spectrum (NMR spectral acquisition parameters optimized for the lens region of the globe) was accomplished through the combination of surgical ablation and difference spectroscopy. The NMR measurements also provided tissue pH values for the lens and cornea. The strengths and limitations of the surface coil NMR method, which is particularly appropriate for in vivo metabolic studies of ocular tissues such as the lens, are discussed.

Pulse Fourier transform water suppression and underwater decoupling in aqueous solutions

Abstract A pulse Fourier transform NMR double-resonance technique is described for simultaneous water suppression and underwater decoupling in 90 to 95% H2O solutions. Suppression of the intense water resonance is achieved via saturation with a selective pulse from the observe rf transmitter. This long soft pulse is applied prior to the nonselective acquisition pulse and is phase shifted from its initial phase by 180° on alternate scans. A requirement of the method, then, is that the observe rf transmitter be capable of switching from a low-power (∼1 W) to a high-power (∼100 W) mode of operation under computer control. Decoupling is achieved with a time-shared homonuclear decoupling field whose rf phase is also shifted by 180° on alternate scans. Spectrometer adjustments which, if not taken into consideration, impede the routine application of the technique, are discussed.

Radioimmunotherapy of human lymphoma in athymic, nude mice as monitored by 31P nuclear magnetic resonance

Human B cell lymphoma (Raji) growing in athymic, nude mice has been successfully treated with a single pulse dose of 131I-labeled monoclonal antibody (Lym-1) specific for this tumor. Sequential in vivo measurements of phosphate metabolites in the tumors by 31P surface coil nuclear magnetic resonance showed a significant initial decrease of phosphocreatine following radioimmunotherapy. Diminution of relative ATP to Pi peak area ratio suggesting tissue damage occurred within 3-4 days. The contribution from metabolites resonating at ca 3.8 ppm (putative sugar phosphate region) increased. There was no significant change in pH either as a function of tumor volume or treatment. The sequence of alterations of nuclear magnetic resonance spectra from tumors of treated mice were strikingly different from sequential nuclear magnetic resonance spectra obtained from tumors of control mice. These observations lead us to conclude that 31P surface coil nuclear magnetic resonance is a promising non-invasive method for assessing and predicting the efficacy of radioimmunotherapy. Further spatial discrimination of the region of tissue observed by the surface coil nuclear magnetic resonance experiment is under exploration in an effort to increase the utility of these methods.