Pei Z M, Baizabal-Aguirre V M, Allen G J, Schroeder J I
Department of Biology and Center for Molecular Genetics, University of California, San Diego, La Jolla, CA 92093-0116, USA.
Proc Natl Acad Sci U S A. 1998 May 26;95(11):6548-53. doi: 10.1073/pnas.95.11.6548.
Sustained (noninactivating) outward-rectifying K+ channel currents have been identified in a variety of plant cell types and species. Here, in Arabidopsis thaliana guard cells, in addition to these sustained K+ currents, an inactivating outward-rectifying K+ current was characterized (plant A-type current: IAP). IAP activated rapidly with a time constant of 165 ms and inactivated slowly with a time constant of 7.2 sec at +40 mV. IAP was enhanced by increasing the duration (from 0 to 20 sec) and degree (from +20 to -100 mV) of prepulse hyperpolarization. Ionic substitution and relaxation (tail) current recordings showed that outward IAP was mainly carried by K+ ions. In contrast to the sustained outward-rectifying K+ currents, cytosolic alkaline pH was found to inhibit IAP and extracellular K+ was required for IAP activity. Furthermore, increasing cytosolic free Ca2+ in the physiological range strongly inhibited IAP activity with a half inhibitory concentration of approximately 94 nM. We present a detailed characterization of an inactivating K+ current in a higher plant cell. Regulation of IAP by diverse factors including membrane potential, cytosolic Ca2+ and pH, and extracellular K+ and Ca2+ implies that the inactivating IAP described here may have important functions during transient depolarizations found in guard cells, and in integrated signal transduction processes during stomatal movements.
在多种植物细胞类型和物种中已鉴定出持续（非失活）外向整流钾离子通道电流。在此，在拟南芥保卫细胞中，除了这些持续的钾离子电流外，还对一种失活外向整流钾离子电流进行了表征（植物A型电流：IAP）。在+40 mV时，IAP以165毫秒的时间常数快速激活，并以7.2秒的时间常数缓慢失活。通过增加预脉冲超极化的持续时间（从0到20秒）和程度（从+20到-100 mV），IAP增强。离子置换和松弛（尾）电流记录表明，外向IAP主要由钾离子携带。与持续外向整流钾离子电流相反，发现胞质碱性pH抑制IAP，且IAP活性需要细胞外钾离子。此外，在生理范围内增加胞质游离钙离子强烈抑制IAP活性，半抑制浓度约为94 nM。我们对高等植物细胞中的一种失活钾离子电流进行了详细表征。包括膜电位、胞质钙离子和pH以及细胞外钾离子和钙离子在内的多种因素对IAP的调节表明，这里描述的失活IAP可能在保卫细胞中发现的瞬时去极化过程以及气孔运动期间的综合信号转导过程中具有重要功能。
