Li Y J, Tan Z Y, Ji Y H
Shanghai Institute of Physiology, Chinese Academy of Sciences, 320 Yue-Yang Road, Shanghai 200031, People's Republic of China.
Neurosci Res. 2000 Nov;38(3):257-64. doi: 10.1016/s0168-0102(00)00164-4.
Binding assay of (125)I-BmK IT2, a depressant insect-selective scorpion toxin showed two non-interacting binding sites on insect neuronal membranes: a high affinity (K(d(1))=0.65+/-0.20 nM) and low capacity (B(max(1))=0.46+/-0.13 pmol/mg protein) binding site, as well as a low-affinity (K(d(2))=78.7+/-16.4 nM) and high capacity (B(max(2))=33.1+/-8.5 pmol/mg protein) binding site. BmK IT2 could associate with and dissociate from its binding sites on insect neuronal membranes in quick manner (k(1)=5.4 x 10(5) S(-1) M(-1) and k(2)=3.2 x 10(4) S(-1) M(-1); k(-1)=7.4 x 10(-4) S(-1) and k(-2)=5.3 x 10(-3) S(-1)). The binding of (125)I-BmK IT2 to insect synaptosomes could be significantly inhibited by native BmK IT2, BmK AS and BmK AS-1 in a dose-dependent manner, and partially by BmK I, but not modified by depolarization of membrane potential and veratridine, In addition, specific binding of (125)I-BmK IT2 seem to be undetectable on rat brain synaptosomes even at high concentration. Whole cell patch-clamping recording found that BmK IT2 could partially inhibit total sodium currents of rat DRG neurons, the inhibitory effects were reversible. The results suggest that the receptor binding site of BmK IT2 on insect sodium channels might be similar to that on sodium channels of mammal peripheral nervous system, but different from that of mammal central nervous system.
一种抑制性昆虫选择性蝎毒素（125）I - BmK IT2的结合试验表明，在昆虫神经元膜上存在两个不相互作用的结合位点：一个高亲和力（Kd(1)=0.65±0.20 nM）和低容量（Bmax(1)=0.46±0.13 pmol/mg蛋白质）的结合位点，以及一个低亲和力（Kd(2)=78.7±16.4 nM）和高容量（Bmax(2)=33.1±8.5 pmol/mg蛋白质）的结合位点。BmK IT2能快速地与昆虫神经元膜上的结合位点结合和解离（k(1)=5.4×10(5) S(-1) M(-1)和k(2)=3.2×10(4) S(-1) M(-1)；k(-1)=7.4×10(-4) S(-1)和k(-2)=5.3×10(-3) S(-1)）。（125）I - BmK IT2与昆虫突触体的结合可被天然的BmK IT2、BmK AS和BmK AS - 1以剂量依赖性方式显著抑制，部分被BmK I抑制，但不受膜电位去极化和藜芦碱的影响。此外，即使在高浓度下，（125）I - BmK IT2在大鼠脑突触体上的特异性结合似乎也无法检测到。全细胞膜片钳记录发现，BmK IT2可部分抑制大鼠背根神经节神经元的总钠电流，其抑制作用是可逆的。结果表明，BmK IT2在昆虫钠通道上的受体结合位点可能与哺乳动物外周神经系统钠通道上的相似，但与哺乳动物中枢神经系统的不同。
