ISSN:
1471-4159
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Medicine
Notes:
Abstract: In the present study, we investigated the existence of a binding site for l-carnitine in the rat brain. In crude synaptic membranes, l-[3H]carnitine bound with relatively high affinity (KD = 281 nM) and in a saturable manner to a finite number (apparent Bmax value = 7.3 pmol/mg of protein) of binding sites. Binding was reversible and dependent on protein concentration, pH, ionic strength, and temperature. Kinetic studies revealed a Koff of 0.018 min−1 and a Kon of 0.187 × 10−3 min−1 nM−1. Binding was highest in spinal cord, followed by medulla oblongata-pons ≥ corpus striatum ≥ cerebellum = cerebral cortex = hippocampus = hypothalamus = olfactory bulb. l-[3H]Carnitine binding was stereoselective for the l-isomers of carnitine, propionylcarnitine, and acetylcarnitine. The most potent inhibitor of l-[3H]carnitine binding was l-carnitine followed by propionyl-l-carnitine. Acetyl-l-carnitine and isobutyryl-l-carnitine showed an affinity ∼500-fold lower than that obtained for l-carnitine. The precursor γ-butyrobetaine had negligible activity at 0.1 mM. l-Carnitine binding to rat crude synaptic membrane preparation was not inhibited by neurotransmitters (GABA, glycine, glutamate, aspartate, acetylcholine, dopamine, norepinephrine, epinephrine, 5-hydroxytryptamine, histamine) at a final concentration of 0.1 mM. In addition, the binding of these neuroactive compounds to their receptors was not influenced by the presence of 0.1 mMl-carnitine. Finally, a subcellular fractionation study showed that synaptic vesicles contained the highest density of l-carnitine membrane binding sites whereas l-carnitine palmitoyltransferase activity was undetectable, thus excluding the possibility of the presence of an active site for carnitine palmitoyltransferase. This finding indicated that the localization of the l-[3H]carnitine binding site should be essentially presynaptic.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1046/j.1471-4159.1995.64062783.x
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