Ibrahim Nurhadi, Bosch Martha A, Smart James L, Qiu Jian, Rubinstein Marcelo, Rønnekleiv Oline K, Low Malcolm J, Kelly Martin J
Department of Physiology and Pharmacology, Oregon Health & Science University, Portland, Oregon 97239-3098, USA.
Endocrinology. 2003 Apr;144(4):1331-40. doi: 10.1210/en.2002-221033.
Hypothalamic proopiomelanocortin (POMC) neurons are critical for controlling homeostatic functions in the mammal. We used a transgenic mouse model in which the POMC neurons were labeled with enhanced green fluorescent protein to perform visualized, whole-cell patch recordings from prepubertal female hypothalamic slices. The mouse POMC-enhanced green fluorescent protein neurons expressed the same endogenous conductances (a transient outward K(+) current and a hyperpolarization-activated, cation current) that have been described for guinea pig POMC neurons. In addition, the selective micro -opioid receptor agonist DAMGO induced an outward current (maximum of 12.8 +/- 1.2 pA), which reversed at K(+) equilibrium potential (E(K+)), in the majority (85%) of POMC neurons with an EC(50) of 102 nM. This response was blocked by the opioid receptor antagonist naloxone with an inhibition constant of 3.1 nM. In addition, the gamma-aminobutyric acid(B) receptor agonist baclofen (40 micro M) caused an outward current (21.6 +/- 4.0 pA) that reversed at E(K+) in these same neurons. The ATP-sensitive potassium channel opener diazoxide also induced an outward K(+) current (maximum of 18.7 +/- 2.2 pA) in the majority (92%) of POMC neurons with an EC(50) of 61 micro M. The response to diazoxide was blocked by the sulfonylurea tolbutamide, indicating that the POMC neurons express both Kir6.2 and sulfonylurea receptor 1 channel subunits, which was verified using single cell RT-PCR. This pharmacological and molecular profile suggested that POMC neurons might be sensitive to metabolic inhibition, and indeed, we found that their firing rate varied with changes in glucose concentrations. Therefore, it appears that POMC neurons may function as an integrator of metabolic cues and synaptic input for controlling homeostasis in the mammal.
下丘脑阿片促黑皮质素原（POMC）神经元对控制哺乳动物的稳态功能至关重要。我们使用了一种转基因小鼠模型，其中POMC神经元用增强型绿色荧光蛋白标记，以对青春期前雌性下丘脑切片进行可视化的全细胞膜片钳记录。小鼠POMC增强型绿色荧光蛋白神经元表达了与豚鼠POMC神经元中描述的相同的内源性电导（一种瞬时外向钾电流和一种超极化激活的阳离子电流）。此外，选择性微阿片受体激动剂DAMGO在大多数（85%）POMC神经元中诱导出外向电流（最大值为12.8±1.2 pA），该电流在钾离子平衡电位（E(K+)）处反转，其半数有效浓度（EC(50)）为102 nM。该反应被阿片受体拮抗剂纳洛酮阻断，抑制常数为3.1 nM。此外，γ-氨基丁酸B（GABA(B)）受体激动剂巴氯芬（40 μM）在这些相同的神经元中引起外向电流（21.6±4.0 pA），该电流在E(K+)处反转。ATP敏感性钾通道开放剂二氮嗪也在大多数（92%）POMC神经元中诱导出外向钾电流（最大值为18.7±2.2 pA），EC(50)为61 μM。对二氮嗪的反应被磺脲类药物甲苯磺丁脲阻断，表明POMC神经元同时表达Kir6.2和磺脲类受体1通道亚基，这通过单细胞逆转录聚合酶链反应（RT-PCR）得到验证。这种药理学和分子特征表明POMC神经元可能对代谢抑制敏感，事实上，我们发现它们的放电频率随葡萄糖浓度的变化而变化。因此，POMC神经元似乎可能作为代谢信号和突触输入的整合器，用于控制哺乳动物的稳态。
