K+ channels of stomatal guard cells. Characteristics of the inward rectifier and its control by pH.
K+ channels of stomatal guard cells. Characteristics of the inward rectifier and its control by pH.
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DOI：
10.1085/jgp.99.4.615
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发表时间：
1992-04
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影响因子：
--
通讯作者：
Blatt MR
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作者：
Blatt MR
用细胞内微电极记录和双电极电压钳技术研究了蚕豆气孔保卫细胞内向整流钾通道的电流特性。从表面上看，电流显示了许多共同的特点，神经肌肉和卵细胞膜的内向整流器。在毫摩尔外部K+浓度（Ko+）下，它在超极化时激活，半衰期为100-200 ms，没有时间或电压依赖性失活的证据，并在钳位至0 mV时迅速失活（τ约10 ms）。稳态电导-电压特性表明表观门控电荷为1.3-1.6。电流反转显示在3- 30 mM范围内对Ko+的能斯特依赖性，并且发现内向整流器对K+的选择性高于其他单价阳离子（K+大于Rb+大于Cs+，远大于Na+）。与动物细胞膜的内向整流器不同，该电流可被Charybdotoxin和alpha-树毒素阻断（Kd远小于50 nM），以及四乙基氯化铵（K1/2 = 9.1 mM）;将保护细胞K+电流的门控固定到接近-120mV的电压，与K 0+无关，而电流仅在超毫摩尔K+（EK+大于-120 mV）时激活。然而，最引人注目的是内向整流敏感性[H+]与K+电流可逆激活温和的酸性外部pH值。电流通过K+内向整流被认为是在很大程度上独立于细胞内的pH值和电流逆转（平衡）电位不受pH值从7.4至5.5。相比之下，通过K+外向整流器的电流先前在这些细胞中表征（1988. J.成员102：235）在很大程度上对pH不敏感，但被可逆地阻断由酸性的细胞内pH。pH对K+内向整流器的作用不能被细胞外Ca 2+模仿，因为其活化、失活和电导的变化与对表面电荷的作用（[Ca 2 +]小于或等于1 mM）一致。相反，细胞外的pH值影响激活和失活动力学不成比例，与酸去pH值提高K+电导和移动的电导-电压曲线正向沿着电压轴和进入生理电压范围。门控的电压和pH依赖性与单个可滴定基团（在-200 mV时pKa约为7）一致，该基团位于膜电场深处，可从外部进入。（400字处截断摘要）
Intracellular microelectrode recordings and a two-electrode voltage clamp have been used to characterize the current carried by inward rectifying K+ channels of stomatal guard cells from the broadbean, Vicia faba L. Superficially, the current displayed many features common to inward rectifiers of neuromuscular and egg cell membranes. In millimolar external K+ concentrations (Ko+), it activated on hyperpolarization with half-times of 100-200 ms, showed no evidence of time- or voltage-dependent inactivation, and deactivated rapidly (tau approximately 10 ms) on clamping to 0 mV. Steady-state conductance- voltage characteristics indicated an apparent gating charge of 1.3-1.6. Current reversal showed a Nernstian dependence on Ko+ over the range 3- 30 mM, and the inward rectifier was found to be highly selective for K+ over other monovalent cations (K+ greater than Rb+ greater than Cs+ much greater than Na+). Unlike the inward rectifiers of animal membranes, the current was blocked by charybdotoxin and alpha- dendrotoxin (Kd much less than 50 nM), as well as by tetraethylammonium chloride (K1/2 = 9.1 mM); gating of the guard cell K+ current was fixed to voltages near -120 mV, independent of Ko+, and the current activated only with supramillimolar K+ outside (EK+ greater than -120 mV). Most striking, however, was inward rectifier sensitivity to [H+] with the K+ current activated reversibly by mild acid external pH. Current through the K+ inward rectifier was found to be largely independent of intracellular pH and the current reversal (equilibrium) potential was unaffected by pHo from 7.4 to 5.5. By contrast, current through the K+ outward rectifier previously characterized in these cells (1988. J. Membr. Biol. 102:235) was largely insensitive to pHo, but was blocked reversibly by acid-going intracellular pH. The action of pHo on the K+ inward rectifier could not be mimicked by extracellular Ca2+ for which changes in activation, deactivation, and conductance were consonant with an effect on surface charge ([Ca2+] less than or equal to 1 mM). Rather, extracellular pH affected activation and deactivation kinetics disproportionately, with acid-going pHo raising the K+ conductance and shifting the conductance-voltage profile positive-going along the voltage axis and into the physiological voltage range. Voltage and pH dependencies for gating were consistent with a single, titratable group (pKa approximately 7 at -200 mV) residing deep within the membrane electric field and accessible from the outside.(ABSTRACT TRUNCATED AT 400 WORDS)