Representative spectra from a perfused db/db heart after 8 min ischemia followed
by 10 minutes reperfusion. A. Dynamic-mode 13C spectra from isolated
db/db heart perfused with 0.4 mM [4,6,8,10,12,14,16 –
13C7] palmitate + 10 mM unlabeled
glucose. Spectra display progressive 13C enrichment of glutamate over
30 minutes. The signals from the 4-, 3-, and 2-carbons of glutamate produced by
oxidation of 13C palmitate, at 34, 28, and 56 ppm respectively (C4,
C3, and C2). C. 13C NMR spectrum of extract from db/db heart perfused
with 13C palmitate + 10 mM unlabeled glucose. The resonance
signals from the 4- and 3-carbons of glutamate at 34 and 28 ppm respectively (C4
and C3) are produced by oxidation of 13C palmitate and display
multiplets from J13C-13C coupling due to glutamate
isotopomer formation. Note the absence of 13C enriched glutamine at
32 ppm the spectrum, which displays enrichment at only the 1.1% natural
abundance level that indicates no significant conversion of 13C
glutamate to glutamine in the heart.