TEMPERATURE-DEPENDENCE OF NMR RELAXATION-TIMES OF NUCLEOSIDE TRIPHOSPHATES AND INORGANIC-PHOSPHATE IN THE ISOLATED-PERFUSED RAT-LIVER - EFFECT ON PI COMPARTMENTATION
S. Dufour et al., TEMPERATURE-DEPENDENCE OF NMR RELAXATION-TIMES OF NUCLEOSIDE TRIPHOSPHATES AND INORGANIC-PHOSPHATE IN THE ISOLATED-PERFUSED RAT-LIVER - EFFECT ON PI COMPARTMENTATION, Journal of magnetic resonance. Series B, 113(2), 1996, pp. 125-135
The effect of temperature on P-31 NMR spectra from isolated perfused r
at livers was studied at 9.4 T. Relaxation times (T-1 and T-2) of nucl
eoside triphosphates (NTP) and inorganic phosphate (Pi) were determine
d at 37, 25, 15, and 4 degrees C. Under hypothermic conditions, an une
xpected apparent line sharpening in the Pi spectral region and a clear
emergence of an additional Pi resonance were observed. This additiona
l signal was assigned to mitochondrial Pi. T-1 values obtained for cyt
osolic and mitochondrial Pi at 4 degrees C were 1.14 +/- 0.24 s (n = 5
) and 0.71 +/- 0.18 s (n = 5), respectively. No significant mitochondr
ial contribution to the Pi resonance was observed at 37 degrees C. Qua
ntification of Pi and NTP liver contents at 37 and 4 degrees C was per
formed by comparing the perfused liver spectrum and the corresponding
perchloric acid extract spectrum. Under experimental conditions of low
external Pi (0.12 mM), it was concluded that intracellular Pi was com
pletely NMR-visible at 4 and 37 degrees C. The observation of the mito
chondrial Pi signal at 4 degrees C was well explained by an increase i
n the Pi level within the matrix, in response to the mitochondrial swe
lling induced by hypothermia, as observed by electron microscopy. T-2
values for the cytosolic Pi at 37 and 4 degrees C were 17 +/- 4 ms (n
= 8) and 22 +/- 4 ms (n = 10), respectively. Comparison with measured
linewidths indicated that line broadening for the main phosphorylated
metabolites-including matrix Pi-was the result of Bo field inhomogenei
ty. The additional broadening of the cytosolic Pi resonance at 4 and 3
7 degrees C was attributed to pH heterogeneity within the liver. (C) 1
996 Academic Press, Inc.