Evaluation of cerebral acetate transport and metabolic rates in the rat brain in vivo using 1H-[13C]-NMR

J Cereb Blood Flow Metab. 2010 Jun;30(6):1200-13. doi: 10.1038/jcbfm.2010.2. Epub 2010 Feb 3.

Abstract

Acetate is a well-known astrocyte-specific substrate that has been used extensively to probe astrocytic function in vitro and in vivo. Analysis of amino acid turnover curves from (13)C-acetate has been limited mainly for estimation of first-order rate constants from exponential fitting or calculation of relative rates from steady-state (13)C enrichments. In this study, we used (1)H-[(13)C]-Nuclear Magnetic Resonance spectroscopy with intravenous infusion of [2-(13)C]acetate-Na(+) in vivo to measure the cerebral kinetics of acetate transport and utilization in anesthetized rats. Kinetics were assessed using a two-compartment (neuron/astrocyte) analysis of the (13)C turnover curves of glutamate-C4 and glutamine-C4 from [2-(13)C]acetate-Na(+), brain acetate levels, and the dependence of steady-state glutamine-C4 enrichment on blood acetate levels. The steady-state enrichment of glutamine-C4 increased with blood acetate concentration until 90% of plateau for plasma acetate of 4 to 5 mmol/L. Analysis assuming reversible, symmetric Michaelis-Menten kinetics for transport yielded 27+/-2 mmol/L and 1.3+/-0.3 micromol/g/min for K(t) and T(max), respectively, and for utilization, 0.17+/-0.24 mmol/L and 0.14+/-0.02 micromol/g/min for K(M_util) and V(max_util), respectively. The distribution space for acetate was only 0.32+/-0.12 mL/g, indicative of a large excluded volume. The astrocytic and neuronal tricarboxylic acid cycle fluxes were 0.37+/-0.03 micromol/g/min and 1.41+/-0.11 micromol/g/min, respectively; astrocytes thus comprised approximately 21%+/-3% of total oxidative metabolism.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Acetates / metabolism*
  • Acetates / pharmacology
  • Animals
  • Astrocytes / metabolism*
  • Biological Transport / physiology
  • Brain / metabolism*
  • Brain Chemistry / physiology
  • Carbon Isotopes
  • Glutamine / metabolism
  • Kinetics
  • Magnetic Resonance Spectroscopy*
  • Neurons / metabolism*
  • Oxidation-Reduction
  • Rats
  • Rats, Sprague-Dawley

Substances

  • Acetates
  • Carbon Isotopes
  • Glutamine