Characterization and subcellular localization of L-[3H] carnitine binding sites in rat brain.
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 x 10(-3) min-1 nM-1. Binding was highest in spinal cord, followed by medulla oblongata-pons > or = corpus striatum > or = 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 approximately 500-fold lower than that obtained for L-carnitine. The precursor gamma-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, acetycholine, 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 mM L-carnitine.(ABSTRACT TRUNCATED AT 250 WORDS)
Vesci
L
L
Department of Pharmacology, Sigma-Tau Company, Pomezia, Rome, Italy.
Tobia
P
P
Corsico
N
N
Martelli
E A
EA
Arduini
A
A
D000818:Animals; D001665:Binding Sites; D001667:Binding, Competitive; D001921:Brain / Q000378:metabolism*; D002331:Carnitine / Q000378:metabolism*; D007700:Kinetics; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D013347:Subcellular Fractions / Q000378:metabolism*; D014018:Tissue Distribution; D014316:Tritium
D014316:Tritium; D002331:Carnitine