Surface charge and lanthanum block of calcium current in bullfrog sympathetic neurons
Surface charge and lanthanum block of calcium current in bullfrog sympathetic neurons
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DOI：
10.1016/s0006-3495(98)77937-8
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发表时间：
1998-05-01
影响因子：
3.4
通讯作者：
Jones, SW
中科院分区：
文献类型：
--
作者：
Block, BM;Stacey, WC;Jones, SW
根据细胞外离子强度对La3+阻断钙通道孔道的影响，估算与钙通道孔相关的表面电荷密度。用全细胞膜片钳技术记录青蛙交感神经元2 mM Ba2+携带的电流。在正常离子强度(120 mM N-甲基-D-葡萄糖胺，NMG)下，La3+以高亲和力阻断该电流(0 mV时IC50=22 nM)。强烈的去极化以时间和电压依赖的方式解除了La3+的阻断。解封后，开放的通道在0 mV时迅速重新阻断，允许估计缔合和解离速率：K(ON)=(7.2+/-0.7)x 10(8)M-1 S(-1)，k(OFF)=10.0+/-0.5 S(-1)。为了评估表面电荷效应，还测量了低离子强度(12.5 mM NMG)和高离子强度(250 MM NMG)下的La3+阻断，La3+阻断的亲和力较高，在12.5 mM NMG下的结合和解离速度快两到三倍，而250 mM的作用很小。实验数据符合Gouy-Chapman理论，其表面电荷密度近似为1e(-)/3000-4000埃(2)。这些结果表明，与电压依赖性钙通道的孔有关的表面电荷很小，但可检测到。
The density of surface charge associated with the calcium channel pore was estimated from the effect of extracellular ionic strength on block by La3+. Currents carried by 2 mM Ba2+ were recorded from isolated frog sympathetic neurons by the whole-cell patch-clamp technique. In normal ionic strength (120 mM N-methyl-D-glucamine, NMG), La3+ blocked the current with high affinity (IC50 = 22 nM at 0 mV). La3+ block was relieved by strong depolarization in a time- and voltage-dependent manner. After unblocking, open channels reblocked rapidly at 0 mV, allowing estimation of association and dissociation rates for La3+: k(on) = (7.2 +/- 0.7) x 10(8) M-1 s(-1), k(off) = 10.0 +/- 0.5 s(-1), To assess surface charge effects, La3+ block was also measured in low ionic strength (12.5 mM NMG) and high ionic strength (250 mM NMG), La3+ block was higher affinity and faster by two-to threefold in 12.5 mM NMG, with little effect of 250 mM NMG, The data could be described by Gouy-Chapman theory with a surface charge density of similar to 1 e(-)/3000-4000 Angstrom(2). These results indicate that there is a small but detectable surface charge associated with the pore of voltage-dependent calcium channels.