Glutamine cycling in isolated working rat heart

Area of Science:

• Cardiovascular Physiology
• Metabolic Biochemistry

Background:

• The role of glutamine in cardiac metabolism is not fully understood.
• Investigating glutamine turnover is crucial for understanding energy balance in the heart.

Purpose of the Study:

• To determine the extent of glutamine turnover relative to oxidative metabolism in the isolated working rat heart.
• To investigate the directionality of glutamine-glutamate exchange under varying substrate conditions.

Main Methods:

• Isolated working rat heart perfusion with different substrate combinations (glucose, pyruvate, propionate) and labeled acetate ([2-13C]acetate).
• Quantification of glutamate and glutamine exchange using ion exchange chromatography and gas chromatography-mass spectrometry (GC-MS).
• Analysis of isotopomer enrichment and glutamine/glutamate ratios using high-resolution nuclear magnetic resonance (NMR) spectroscopy.

Main Results:

• Fractional enrichment in glutamine was 31% of glutamate enrichment across different perfusates.
• High glutamine to glutamate ratios (53.4-96.9%) were observed.
• While [1-13C]glutamine was detected in the heart, 13C transfer from glutamine to glutamate was not detected.

Conclusions:

• Glutamine production via amidation of glutamate is an active and detectable process in the perfused working rat heart.
• The reverse reaction, glutamate generation from glutamine, was not detected under these experimental conditions.
• Glutamine synthesis appears to keep pace with oxidative metabolism, but its breakdown is not evident.