INWARD RECTIFIER POTASSIUM CHANNELS IN PLANTS DIFFER FROM THEIR ANIMAL COUNTERPARTS IN RESPONSE TO VOLTAGE AND CHANNEL MODULATORS
INWARD RECTIFIER POTASSIUM CHANNELS IN PLANTS DIFFER FROM THEIR ANIMAL COUNTERPARTS IN RESPONSE TO VOLTAGE AND CHANNEL MODULATORS
复制标题
DOI：
10.1007/bf00211406
复制
发表时间：
1995-10-01
期刊：
影响因子：
--
通讯作者：
PALME, K
中科院分区：
文献类型：
--
作者：
HEDRICH, R;MORAN, O;PALME, K
我们研究了非洲爪蟾卵母细胞中表达的拟南芥KAT1基因产物钾向内矫正的电生理基础，以及蚕豆和蚕豆的保护细胞和根细胞质膜中功能相关的Kf通道。通过这些通道的全细胞电流被激活，随后的步骤使膜电位大于-100毫伏，激活时间减半为几十毫秒。这种电压依赖性不受细胞质镁去除的影响。因此，与动物的内向整流通道不同，植物钾通道的内向整流是通道蛋白本身的内在特性。我们还发现KAT1的活化动力学受到外部pH的调节，在8.5 ~ 4.5范围内降低pH会加速活化，并且每pH单位会使稳态活化曲线移动19 mV。这表明这些K+通道的活性和质膜H+- atp酶的活性可能不仅受到膜电位的协调，而且受到pH的协调。另一方面，瞬时电流-电压关系不依赖于pH，表明H+不会阻断通道。除了对质子的敏感性外，通道在铯存在时显示出高亲和力电压依赖块，但对钡不太敏感。在对称、不含Mg2+、100 mM-K+的溶液中，对注射KAT1的卵母细胞的膜片进行记录，可以测量单个开放的KAT1通道的电流-电压关系，其单一电导为5ps。我们得出结论，KAT1基因产物介导的电流向内整流，或植物细胞的相关内源通道，是由通道蛋白内电压调节的结构变化引起的。电压感应或门控结构似乎与暴露于细胞外介质的可滴定的酸性残留物相互作用。
We have investigated the electrophysiological basis of potassium inward rectification of the KAT1 gene product from Arabidopsis thaliana expressed in Xenopus oocytes and of functionally related Kf channels in the plasmamembrane of guard and root cells from Vicia faba and Zen mays. The whole-cell currents passed by these channels activate, following steps to membrane potentials more negative than -100 mV, with half activation times of tens of milliseconds. This voltage dependence was unaffected by the removal of cytoplasmic magnesium. Consequently, unlike inward rectifier channels of animals, inward rectification of plant potassium channels is an intrinsic property of the channel protein itself. We also found that the activation kinetics of KAT1 were modulated by external pH. Decreasing the pH in the range 8.5 to 4.5 hastened activation and shifted the steady state activation curve by 19 mV per pH unit. This indicates that the activity of these K+ channels and the activity of the plasma membrane H+-ATPase may not only be coordinated by membrane potential but also by pH. The instantaneous current-voltage relationship, on the other hand, did not depend on pH, indicating that H+ do not block the channel. In addition to sensitivity towards protons, the channels showed a high affinity voltage dependent block in the presence of cesium, but were less sensitive to barium. Recordings from membrane patches of KAT1 injected oocytes in symmetric, Mg2+-free, 100 mM-K+, solutions allowed measurements of the current-voltage relation of single open KAT1 channels with a unitary conductance of 5 pS. We conclude that the inward rectification of the currents mediated by the KAT1 gene product, or the related endogenous channels of plant cells, results from voltage-modulated structural changes within the channel proteins. The voltage-sensing or the gating-structures appear to interact with a titratable acidic residue exposed to the extracellular medium.