Schroeder J I
Max-Planck-Institut für Biophysikalische Chemie, Abteilung Membranbiophysik, Göttingen, Federal Republic of Germany.
J Gen Physiol. 1988 Nov;92(5):667-83. doi: 10.1085/jgp.92.5.667.
Electrical properties of the plasma membrane of guard cell protoplasts isolated from stomates of Vicia faba leaves were studied by application of the whole-cell configuration of the patch-clamp technique. The two types of K+ currents that have recently been identified in guard cells may allow efflux of K+ during stomatal closing, and uptake of K+ during stomatal opening (Schroeder et al., 1987). A detailed characterization of ion transport properties of the inward-rectifying (IK+,in) and the outward-rectifying (IK+,out) K+ conductance is presented here. The permeability ratios of IK+,in and IK+,out currents for K+ over monovalent alkali metal ions were determined. The resulting permeability sequences (PK+ greater than PRb+ greater than PNa+ greater than PLi+ much greater than PCs+) corresponded closely to the ion specificity of guard cell movements in V. faba. Neither K+ currents exhibited significant inactivation when K+ channels were activated for prolonged periods (greater than 10 min). The absence of inactivation may permit long durations of K+ fluxes, which occur during guard cell movements. Activation potentials of inward K+ currents were not shifted when external K+ concentrations were changed. This differs strongly from the behavior of inward-rectifying K+ channels in animal tissue. Blue light and fusicoccin induce hyperpolarization by stimulation of an electrogenic pump. From slow-whole-cell recordings it was concluded that electrogenic pumps require cytoplasmic substrates for full activation and that the magnitude of the pump current is sufficient to drive K+ uptake through IK+,in channels. First, direct evidence was gained for the hypothesis that IK+,in channels are a molecular pathway for K+ accumulation by the finding that IK+,in was blocked by Al3+ ions, which are known to inhibit stomatal opening but not closing. The results presented in this study strongly support a prominent role for IK+,in and IK+,out channels in K+ transport across the plasma membrane of guard cells.
采用膜片钳技术的全细胞模式，对从蚕豆叶片气孔分离出的保卫细胞原生质体的质膜电学特性进行了研究。最近在保卫细胞中鉴定出的两种类型的钾离子电流，可能在气孔关闭时允许钾离子外流，在气孔开放时允许钾离子内流（施罗德等人，1987年）。本文对内向整流（IK +，in）和外向整流（IK +，out）钾离子电导的离子转运特性进行了详细表征。测定了IK +，in和IK +，out电流对钾离子与单价碱金属离子的渗透率比值。所得的渗透率序列（PK +＞PRb +＞PNa +＞PLi +＞＞PCs +）与蚕豆保卫细胞运动的离子特异性密切相关。当钾离子通道长时间（＞10分钟）激活时，两种钾离子电流均未表现出明显的失活。失活的缺失可能允许在保卫细胞运动期间发生长时间的钾离子通量。当外部钾离子浓度改变时，内向钾离子电流的激活电位没有偏移。这与动物组织中内向整流钾离子通道的行为有很大不同。蓝光和壳梭孢菌素通过刺激生电泵诱导超极化。从慢全细胞记录中得出结论，生电泵需要细胞质底物才能完全激活，并且泵电流的大小足以驱动钾离子通过IK +，in通道内流。首先，通过发现IK +，in被Al3 +离子阻断，获得了直接证据支持IK +，in通道是钾离子积累的分子途径这一假设，已知Al3 +离子抑制气孔开放但不抑制关闭。本研究中呈现的结果有力地支持了IK +，in和IK +，out通道在保卫细胞质膜钾离子转运中起重要作用。
