Seagar M J, Deprez P, Martin-Moutot N, Couraud F
Brain Res. 1987 May 19;411(2):226-30. doi: 10.1016/0006-8993(87)91073-0.
Apamin, an 18-amino acid bee venom peptide, is a specific blocker of a class of Ca2+ activated K+ channels. Mono 125I-iodoapamin was used to detect the K+ channel-associated receptor site in cultured astrocytes from rat brain. Specific high-affinity binding to intact glial cells with a Kd of about 90 pM at 1 degree C and pH 7.5 was demonstrated by equilibrium and kinetic methods. The average receptor capacity was 3 fmol/mg cell protein which is 2 to 3-fold lower than in primary cultured neurons. Binding was stimulated by K+ ions, but to a lesser extent than with neuronal receptors. Photoaffinity labeling of receptor/ion channel components using an arylazide derivative of 125I-monoiodoapamin revealed the presence of the 86- and 33-kDa polypeptides, previously detected in neurones. However a 59-kDa peptide which is present in synaptic membrane preparations from adult rat brain, but not in cultured neurons, was also clearly labeled in intact astrocytes. This indicates that the 59-kDa polypeptide is not a proteolytic fragment of the 86-kDa chain but an associated subunit which is only accessible to photolabeling in certain apamin receptor preparations. Apamin-sensitive Ca2+-activated K+ channels in astrocytes may be one of the pathways by which glial cells redistribute K+ in the central nervous system (CNS).
蜂毒明肽是一种由18个氨基酸组成的蜂毒肽，是一类钙离子激活钾通道的特异性阻滞剂。用单碘-125I-蜂毒明肽检测大鼠脑培养星形胶质细胞中与钾通道相关的受体位点。通过平衡和动力学方法证明，在1℃和pH 7.5条件下，与完整胶质细胞具有特异性高亲和力结合，解离常数约为90 pM。平均受体容量为3 fmol/mg细胞蛋白，比原代培养神经元低2至3倍。钾离子可刺激结合，但程度低于神经元受体。使用125I-单碘蜂毒明肽的芳基叠氮衍生物对受体/离子通道成分进行光亲和标记，发现了先前在神经元中检测到的86 kDa和33 kDa多肽。然而，在成年大鼠脑突触膜制剂中存在但在培养神经元中不存在的59 kDa肽，在完整星形胶质细胞中也被清晰标记。这表明59 kDa多肽不是86 kDa链的蛋白水解片段，而是一个相关亚基，仅在某些蜂毒明肽受体制剂中可被光标记。星形胶质细胞中对蜂毒明肽敏感的钙离子激活钾通道可能是胶质细胞在中枢神经系统（CNS）中重新分布钾离子的途径之一。
