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J W Pan

Publications and source records attributed to J W Pan.

42 records · Page 3Linked to original sources
PubMed1994

Evaluation of cerebral gray and white matter metabolite differences by spectroscopic imaging at 4.1T.

Using a 4.1T whole body system, we have acquired 1H spectroscopic imaging (SI) data of N-acetyl (NA) compounds, creatine (CR), and choline (CH) with nominal voxel sizes of 0.5 cc (1.15 cc after filtering). We have used the SI data to estimate differences in cerebral metabolites of human gray and white matter. To evaluate the origin of an increased CR/NA and CH/NA ratios in gray matter relative to white matter, we measured the T1 and T2 of CR, NA, and CH in gray and white matter using moderate resolution SI imaging. In white matter the T2s of NA, CR, and CH were 233 +/- 27, 141 +/- 18, and 167 +/- 20 ms, respectively, and 227 +/- 27, 140 +/- 16, and 189 +/- 25 ms in gray matter. The T1 values for NA, CR, and CH were 1267 +/- 141, 1487 +/- 146, and 1111 +/- 136 ms in gray matter and 1260 +/- 154, 1429 +/- 233, and 1074 +/- 146 ms in white matter. After correcting for T1 and T2 losses, creatine content was significantly lower in white matter than gray (P < 0.01, t-test), with a white/gray content ratio of 0.8, in agreement with biopsy and in vivo measurements at 1.5 and 2.0T.

Aspartic Acid↗
PubMed1991

Quantitation of metabolites by 1H NMR.

In this report we describe the three factors that need to be measured when quantitating an edited resonance relative to an internal standard using a surface coil. These factors are necessary by virtue of the water, fat suppressing, and localization schemes used in studing a 1H metabolite. First, use of semi-selective pulses requires amplitude correction of the edited and reference resonances. Second, use of a single surface coil results in different sensitive volumes for different resonances due to the inhomogeneous B1 and therefore require separate acquisition of the resonances. Third, editing pulses alter the sensitive volumes and this correction must be made internally by applying the same editing pulse to the reference resonance. A rationalization of this correction is given in terms of rotation operators. We apply these corrections to quantitate edited lactate relative to total creatine in a MnCl2-doped phantom and find 91% rather than 145% of known concentration. In human skeletal muscle in vivo after exhaustive exercise, we measured the lactate after exercise and found it to be 27.2 mM in two experiments, in reasonable agreement with literature values for the given exercise protocol.

Adult↗
PubMed1991

Correlation of lactate and pH in human skeletal muscle after exercise by 1H NMR.

We have made in vivo 1H NMR measurements of the time course of pH and lactate in human skeletal muscle after exercise. Spectra were obtained in a 4.7-T 30-cm bore Bruker Biospec spectrometer with a 2.5-cm diameter single surface coil. pH was determined from the shift of the endogenous carnosine H-C2 peak while lactate concentrations were determined by comparison with endogenous total creatine, taken to be 28.5 mM/kg wet wt. Fitting the data shows that the exponential decay of lactate (-0.094 +/- 0.014 min-1. t1/2 = 10.6 min) is slower than that of pH (-0.147 +/- 0.015 min-1, t1/2 = 4.7 min), n = 7 with two different volunteers. These values are significantly different with P less than 0.0005. Relaxation times of lactate and creatine were also measured for lactate quantitation; creatine T1, 1.23 +/- 12 s, T2, 136.2 +/- 26.4 ms (both in resting human muscle); lactate T1 (in postmortem rabbit muscle), 1.0 +/- 11 s and T2, 80 ms (in postexercise human muscle). At the end of intense exercise, the lactate level reached was 25.3 +/- 4.0 mM and the average pH drop was 1.0 pH unit. We discuss the implications of these measurements in conjunction with existing data on other sources of H+ flux, phosphocreatine resynthesis, H+ transport, and contribution of inorganic phosphate to buffering.

Adult↗
PubMed1990

Steady-state measurements of Escherichia coli sodium and proton potentials at alkaline pH support the hypothesis of electrogenic antiport.

31P and 23Na NMR spectroscopy was applied to the measurement of proton and sodium potentials in endogenously respiring Escherichia coli cells over an external pH (pHex) range from mildly acidic (6.4) to fairly alkaline (8.4). Stable maintenance of alkaline pHex in the face of metabolic acidification was achieved by use of a perfusion system. In the acidic to neutral pHex range, the sodium chemical potential followed the proton chemical potential quite closely, although always exceeding it slightly, as has been reported previously (Castle, A. M., Macnab, R. M., and Shulman, R. G. (1986) J. Biol. Chem. 261, 7797-7806). Above pHex 7.4, the sodium potential changed abruptly from a decreasing to an increasing function of pHex, whereas the proton potential continued to decrease. As a consequence, the apparent stoichiometry (i.e. the ratio between the sodium and proton electrochemical potentials) took on progressively higher values, increasing from approximately 1.1 at pH 7.4 to approximately 1.3 at pH 7.8. Thereafter, the sodium chemical potential started to decrease again; however, since the decrease was less steep than that of the proton potential, the apparent stoichiometry continued to increase. At the highest pHex examined (8.4), it had reached a value of approximately 1.4. These results strongly support the hypothesis of an electroneutral (1:1) H+/Na+ antiporter operating virtually alone under acidic to neutral conditions and then being supplemented to an ever increasing degree by an electrogenic (for example, 2:1) antiporter under more alkaline conditions.

Biological Transport↗
PubMed1988

Intracellular pH in human skeletal muscle by 1H NMR.

We report here the in vivo observation of the imidazole protons (C-2 and C-4) of carnosine (beta-Ala-His) by 1H NMR at 4.7 T in human skeletal muscle. The relationship between the pH and chemical shift of the C-2 and C-4 resonances was determined analytically. These titration curves were used to measure the resting pH of human muscle in vivo, 7.01 x 0.04 (C-2 proton) and 6.97 +/- 0.10 (C-4 proton). An in vivo titration curve of the C-2 proton resonance was determined by interleaving 1H and 31P NMR spectra after exhaustive exercise, during which muscle pH recovers from an acidic value of 6.1. We observed excellent agreement between the pH values as determined by the C-2 resonance of carnosine and that of inorganic phosphate. Carnosine provides an excellent pH indicator since (i) its concentration is relatively stable and (ii) it allows measurement of proton metabolites and pH to be achieved through the same coil, thus enabling a better signal/noise ratio and better localization.

Algorithms↗