Cu C, Bähring R, Mayer M L
Laboratory of Cellular and Molecular Neurophysiology, NICHD, National Institute of Health, Bethesda, MD 20892, USA.
Neuropharmacology. 1998 Oct-Nov;37(10-11):1381-91. doi: 10.1016/s0028-3908(98)00112-9.
Block of kainate subtype glutamate receptor channels by internal polyamines was analysed using outside out patches from HEK 293 cells transiently transfected with GluR6(Q). Tetramines with different numbers and spacing of methylene groups between NH2 groups produced biphasic rectification well fit by the Woodhull model for a weakly permeable ion channel blocker. Such analysis revealed an increase in binding energy of 611 cal M(-1) for each methylene group added over the range 6-12 (CH2), suggesting that a major component of block by polyamines involves hydrophobic binding. Isomers with the same number of CH2 groups but different spacing between NH2 groups showed similar affinity. Due to differences in pKa values for protonation of NH2 groups, the average charge on the tetramines studied would be expected to vary from 3.98 to 2.22 at physiological pH; despite this, the voltage dependence of block was similar for all tetramines tested, with a mean value for ztheta of 1.82, similar to values for polyamines with five or six NH2 groups. In contrast, for 1,3-propane diamine (DA3 ztheta 0.83), and the N-propyl- (ztheta 1.42) and N,N'-diethyl- (ztheta 1.37) analogues of DA3, there was an increase in the voltage dependence of block on addition of hydrophobic groups.
利用从瞬时转染了GluR6(Q)的HEK 293细胞获得的外侧膜片，分析了内部多胺对红藻氨酸亚型谷氨酸受体通道的阻断作用。在NH₂基团之间具有不同亚甲基数量和间隔的四胺产生了双相整流，这种双相整流很好地符合了弱渗透离子通道阻滞剂的伍德胡尔模型。这样的分析揭示了在6至12个（CH₂）范围内每添加一个亚甲基结合能增加611 cal M⁻¹，这表明多胺阻断的一个主要成分涉及疏水结合。具有相同CH₂基团数量但NH₂基团之间间隔不同的异构体表现出相似的亲和力。由于NH₂基团质子化的pKa值存在差异，在所研究的四胺上的平均电荷在生理pH下预计会在3.98至2.22之间变化；尽管如此，所有测试的四胺的阻断电压依赖性相似，zθ的平均值为1.82，与具有五个或六个NH₂基团的多胺的值相似。相比之下，对于1,3 - 丙二胺（DA3，zθ为0.83），以及DA3的N - 丙基 - （zθ为1.42）和N,N'-二乙基 - （zθ为1.37）类似物，添加疏水基团后阻断的电压依赖性增加。
