Vesci L, Tobia P, Corsico N, Martelli E A, Arduini A
Department of Pharmacology, Sigma-Tau Company, Pomezia, Rome, Italy.
J Neurochem. 1995 Jun;64(6):2783-91. doi: 10.1046/j.1471-4159.1995.64062783.x.
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)
在本研究中，我们调查了大鼠脑中左旋肉碱结合位点的存在情况。在粗制突触膜中，L-[³H]肉碱以相对较高的亲和力（KD = 281 nM）且以可饱和的方式与有限数量（表观Bmax值 = 7.3 pmol/mg蛋白质）的结合位点结合。结合是可逆的，且依赖于蛋白质浓度、pH、离子强度和温度。动力学研究显示解离常数Koff为0.018 min⁻¹，结合常数Kon为0.187×10⁻³ min⁻¹ nM⁻¹。结合在脊髓中最高，其次是延髓 - 脑桥≥纹状体≥小脑 = 大脑皮层 = 海马体 = 下丘脑 = 嗅球。L-[³H]肉碱结合对肉碱、丙酰肉碱和乙酰肉碱的L-异构体具有立体选择性。L-[³H]肉碱结合的最有效抑制剂是左旋肉碱，其次是丙酰-L-肉碱。乙酰-L-肉碱和异丁酰-L-肉碱的亲和力比左旋肉碱低约500倍。前体γ-丁甜菜碱在0.1 mM时活性可忽略不计。终浓度为0.1 mM时，神经递质（γ-氨基丁酸、甘氨酸、谷氨酸、天冬氨酸、乙酰胆碱、多巴胺、去甲肾上腺素、肾上腺素、5-羟色胺、组胺）不抑制左旋肉碱与大鼠粗制突触膜制剂的结合。此外，这些神经活性化合物与其受体的结合不受0.1 mM左旋肉碱存在的影响。（摘要截短于250字）
