Varga Z, Panyi G, Péter M, Pieri C, Csécsei G, Damjanovich S, Gáspár R
Department of Biophysics and Cell Biology, University Medical School of Debrecen, Debrecen H-4012, Hungary.
Biophys J. 2001 Mar;80(3):1280-97. doi: 10.1016/S0006-3495(01)76103-6.
Melatonin is a small amino acid derivative hormone of the pineal gland. Melatonin quickly and reversibly blocked Kv1.3 channels, the predominant voltage-gated potassium channel in human T-lymphocytes, acting from the extracellular side. The block did not show state or voltage dependence and was associated with an increased inactivation rate of the current. A half-blocking concentration of 1.5 mM was obtained from the reduction of the peak current. We explored several models to describe the stoichiometry of melatonin-Kv1.3 interaction considering one or four independent binding sites per channel. The model in which the occupancy of one of four binding sites by melatonin is sufficient to block the channels gives the best fit to the dose-response relationship, although all four binding sites can be occupied by the drug. The dissociation constant for the individual binding sites is 8.11 mM. Parallel application of charybdotoxin and melatonin showed that both compounds can simultaneously bind to the channels, thereby localizing the melatonin binding site out of the pore region. However, binding of tetraethylammonium to its receptor decreases the melatonin affinity, and vice versa. Thus, the occupancy of the two separate receptor sites allosterically modulates each other.
褪黑素是松果体分泌的一种小分子氨基酸衍生物激素。褪黑素能快速且可逆地阻断Kv1.3通道，该通道是人类T淋巴细胞中主要的电压门控钾通道，作用于细胞外侧。这种阻断不表现出状态或电压依赖性，且与电流失活速率增加有关。通过峰值电流的降低得到半阻断浓度为1.5 mM。我们探索了几种模型来描述褪黑素与Kv1.3相互作用的化学计量关系，考虑每个通道有一个或四个独立的结合位点。尽管药物可以占据所有四个结合位点，但褪黑素占据四个结合位点之一就足以阻断通道的模型最符合剂量反应关系。单个结合位点的解离常数为8.11 mM。同时应用蝎毒素和褪黑素表明，这两种化合物可以同时结合到通道上，从而将褪黑素结合位点定位在孔区之外。然而，四乙铵与其受体的结合会降低褪黑素的亲和力，反之亦然。因此，两个独立受体位点的占据会相互变构调节。
