Dimensions and ion selectivity of recombinant AMPA and kainate receptor channels and their dependence on Q/R site residues
Dimensions and ion selectivity of recombinant AMPA and kainate receptor channels and their dependence on Q/R site residues
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DOI：
10.1113/jphysiol.1996.sp021674
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发表时间：
1996-10-01
影响因子：
5.5
通讯作者：
Sakmann, B
中科院分区：
文献类型：
--
作者：
Burnashev, N;Villarroel, A;Sakmann, B
1. 重组α -氨基-3-羟基-5-甲基-4-异恶唑丙酸受体（AMPAR）亚基（GluR-A或GluR-B）和kainate受体（KAR）亚基（GluR-6）在HEK 293细胞中以未编辑(Q)和编辑(R)形式表达。为了估计这些通道狭窄部分的尺寸，以Cs+为内参离子，测定了不同平均直径有机阳离子的生物离子反转电位。由q型亚基组装的同质通道具有阳离子选择性。相对渗透率与不同有机阳离子的平均尺寸的关系表明，AMPAR和KAR通道的q型通道狭窄部分的直径分别约为0.78 nm和0.75 nm。由r型亚基组装而成的同质通道渗透到阴离子和阳离子中。当用CsCl梯度探测时，GluR-B(R)的相对氯离子渗透率（P-Ol/P-Cs）估计为0.14,GluR-G(R)亚基通道的相对氯离子渗透率为0.74。用弱渗透的F- as阴离子测量的大阳离子的渗透率与平均尺寸的关系表明，r型KAR通道的表观孔径接近0.76 nm。由Q型和r型亚基共同组装的异质AMPAR和KAR通道具有阳离子选择性。这些通道狭窄部分的直径估计在0.70至0.74 nm之间。结果表明，不同亚基组成和不同离子选择性的AMPAR和KAR通道狭窄部分的直径具有可比性。因此，阴离子与阳离子选择性、Ca2+渗透率和通道电导率的差异可能是由通道电荷密度的差异决定的。
1. Recombinant alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropopionate receptor (AMPAR) subunits (GluR-A or GluR-B) and kainate receptor (KAR) subunit (GluR-6) in their unedited (Q)- and edited (R)-forms were expressed in HEK 293 cells. To estimate the dimensions of the narrow portion of these channels, biionic reversal potentials for organic cations of different mean diameters were determined with Cs+ as the internal reference ion.2. Homomeric channels assembled from Q-form subunits were cation selective. The relation between the relative permeability and the mean size of different organic cations suggests that the diameter of the narrow portion of Q-form channels is approximately 0.78 nm for AMPAR and 0.75 nm for KAR channels.3. Homomeric channels assembled from R-form subunits were permeant fur anions and cations. When probed with CsCl gradients the relative chloride permeability (P-Ol/P-Cs) was estimated as 0.14 fur GluR-B(R) and 0.74 for GluR-G(R)-subunit channels. The permeability versus mean size relation for large cations measured with the weakly permeant F- as anion, indicates that for the R-form KAR channels thr apparent pore diameter is close to 0.76 nm.4. Heteromeric AMPAR and KAR channels co-assembled from Q- and R-form subunits were cation selective. The diameter of the narrow portion of these channels is estimated to be in the range between 0.70 and 0.74 nm.5. The results indicate that the diameters of the narrow portion of AMPAR and KAR channels of different subunit composition and of widely different ion selectivity are comparable. Therefore, the differences in the anion versus cation selectivity, in Ca2+ permeability and in channel conductance are likely to be determined by the difference in charge density of the channel.