Marrannes R, De Prins E
Central Nervous System Discovery Research, Janssen Research Foundation, Beerse, Belgium.
J Pharmacol Exp Ther. 2000 Nov;295(2):531-45.
Besides other pharmacological effects, the neuroprotective compound lubeluzole blocks low-voltage-activated (iLVA) and high-voltage-activated (iHVA) calcium channel currents. We investigated the site of action of lubeluzole on Ca(2+) channels in isolated dorsal root ganglion cells of the rat, using whole-cell voltage clamp. Experiments with extracellular application of 3 microM lubeluzole (pK(a) = 7.6) at different values of extracellular pH suggest that the protonated form of lubeluzole contributes to the block of iLVA and iHVA from the extracellular side. The partial block of iLVA and iHVA by 3 microM lubeluzole at extracellular pH 9 and intracellular pH (pH(i)) 9 indicates that the uncharged form of lubeluzole (L) may contribute to the block as well. The voltage-dependent acceleration of the apparent inactivation of iHVA by lubeluzole was much more pronounced at lower pH(i), which is consistent with membrane penetration of L and an open channel block of iHVA by the prononated form of lubeluzole acting from the intracellular side. Decreasing pH(i) induced a negative shift of the half-inactivation potential of iLVA and increased the lubeluzole-induced block of iLVA. Experiments with extracellular or intracellular application of a quaternary ammonium derivative of lubeluzole (R133121), which was less potent than lubeluzole, support the above conclusions on the side of action of lubeluzole. Application of lubeluzole via the patch pipette affected iLVA and iHVA only minimally compared with extracellular application, probably partly due to efflux of L through the cell membrane. These experiments suggest that lubeluzole blocks Ca(2+) channels from both the extracellular and the intracellular side.
除了其他药理作用外，神经保护化合物鲁贝唑可阻断低电压激活（iLVA）和高电压激活（iHVA）的钙通道电流。我们使用全细胞膜片钳技术，研究了鲁贝唑在大鼠离体背根神经节细胞钙通道上的作用位点。在不同细胞外pH值下，细胞外施加3 microM鲁贝唑（pK(a)=7.6）的实验表明，鲁贝唑的质子化形式从细胞外侧有助于阻断iLVA和iHVA。在细胞外pH 9和细胞内pH（pH(i)）9时，3 microM鲁贝唑对iLVA和iHVA的部分阻断表明，鲁贝唑的不带电形式（L）也可能有助于阻断。鲁贝唑对iHVA表观失活的电压依赖性加速在较低pH(i)时更为明显，这与L的膜穿透以及鲁贝唑的质子化形式从细胞内侧对iHVA的开放通道阻断一致。降低pH(i)导致iLVA的半失活电位负移，并增加鲁贝唑对iLVA的阻断。用鲁贝唑的季铵衍生物（R133121）进行细胞外或细胞内应用实验，其效力低于鲁贝唑，支持了上述关于鲁贝唑作用位点的结论。与细胞外应用相比，通过膜片吸管应用鲁贝唑对iLVA和iHVA的影响极小，这可能部分是由于L通过细胞膜外流。这些实验表明，鲁贝唑可从细胞外和细胞内侧阻断钙通道。
