Gao Xiao-Bing, van den Pol Anthony N
Department of Neurosurgery, Yale University School of Medicine, New Haven, CT 06520, USA.
J Physiol. 2002 Jul 1;542(Pt 1):273-86. doi: 10.1113/jphysiol.2002.019372.
Melanin-concentrating hormone (MCH), a cyclic 19-amino-acid peptide, is synthesized exclusively by neurons in the lateral hypothalamic (LH) area. It is involved in a number of brain functions and recently has raised interest because of its role in energy homeostasis. MCH axons and receptors are found throughout the brain. Previous reports set the foundation for understanding the cellular actions of MCH by using non-neuronal cells transfected with the MCH receptor gene; these cells exhibited an increase in cytoplasmic calcium in response to MCH, suggesting an excitatory action for the peptide. In the study presented here, we have used whole-cell recording in 117 neurons from LH cultures and brain slices to examine the actions of MCH. MCH decreased the amplitude of voltage-dependent calcium currents in almost all tested neurons. The inhibition desensitized rapidly (18 s to half maximum at 100 nM concentration) and was dose-dependent (IC(50) = 7.8 nM) when activated with a pulse from -80 mV to 0 mV. A priori activation of G-proteins with GTPgammaS completely eliminated the MCH-induced effect at low MCH concentrations and reduced the MCH-induced effect at high MCH concentrations. Inhibition of G-proteins with pertussis toxin (PTX) blocked the MCH-induced inhibitory effect at high MCH concentrations. Pre-pulse depolarization resulted in an attenuation of the MCH-induced inhibition of calcium currents in most neurons. These data suggest that MCH exerts an inhibitory effect on calcium currents via PTX-sensitive G-protein pathways, probably the G(i)/G(o) pathway, in LH neurons. L-, N- and P/Q-type calcium channels were identified in LH neurons, with L- and N-type channels accounting for most of the voltage-activated current (about 40 % each); MCH attenuated each of the three types (mean 50 % depression), with the greatest inhibition found for N-type currents. In contrast to previous data on non-neuronal cells showing an MHC-evoked increase in calcium, our data suggest that the reverse occurs in LH neurons. The attenuation of calcium currents is consistent with an inhibitory action for the peptide in neurons.
促黑素（MCH）是一种由19个氨基酸组成的环状肽，仅由下丘脑外侧（LH）区域的神经元合成。它参与多种脑功能，最近因其在能量稳态中的作用而受到关注。MCH轴突和受体遍布整个大脑。先前的报告通过使用转染了MCH受体基因的非神经元细胞，为理解MCH的细胞作用奠定了基础；这些细胞在对MCH的反应中表现出细胞质钙增加，表明该肽具有兴奋作用。在本文所述的研究中，我们使用全细胞记录技术，对来自LH培养物和脑片的117个神经元进行研究，以检验MCH的作用。MCH几乎在所有测试神经元中降低了电压依赖性钙电流的幅度。当用从-80 mV到0 mV的脉冲激活时，这种抑制作用迅速脱敏（在100 nM浓度下18秒达到最大抑制的一半）且呈剂量依赖性（IC(50)=7.8 nM）。用GTPγS预先激活G蛋白，在低MCH浓度下完全消除了MCH诱导的效应，在高MCH浓度下降低了MCH诱导的效应。用百日咳毒素（PTX）抑制G蛋白，在高MCH浓度下阻断了MCH诱导的抑制效应。预脉冲去极化导致大多数神经元中MCH诱导的钙电流抑制作用减弱。这些数据表明，MCH通过PTX敏感的G蛋白途径，可能是G(i)/G(o)途径，对LH神经元中的钙电流发挥抑制作用。在LH神经元中鉴定出了L型、N型和P/Q型钙通道，其中L型和N型通道占大部分电压激活电流（各约40%）；MCH减弱了这三种类型的电流（平均抑制50%），对N型电流的抑制作用最大。与先前关于非神经元细胞显示MHC引起钙增加的数据相反，我们的数据表明在LH神经元中情况相反。钙电流的减弱与该肽在神经元中的抑制作用一致。
