Wu W. H., Assmann S. M.
Department of Biology, The Pennsylvania State University, 208 Mueller Laboratory, University Park, Pennsylvania 16802.
Plant Physiol. 1995 Jan;107(1):101-109. doi: 10.1104/pp.107.1.101.
In vivo, K+ entry into guard cells via inward-rectifying K+ channels is indirectly driven by ATP via an H+-ATPase that hyperpolarizes the membrane potential. However, whether activation of the K+ channels of guard cells requires ATP remains unknown. In the present study, both whole-cell and single-channel patch-clamp techniques were used to address this question. Exogenous ATP, ADP, and adenosine-5[prime]-O-(3-thiotriphosphate) applied to the cytoplasm had no effect on whole-cell K+ currents of Vicia faba L. guard cells. Azide, an inhibitor of oxidative phosphorylation, also had no effect. However, an ATP-scavenging system, glucose plus hexokinase, inhibited whole-cell inward K+ currents by 30 to 40%. Single-channel results acquired from cytoplasm-free inside-out membrane patches showed definite activation of inward K+ channels by ATP. Other nucleotides, such as ADP, adenosine-5[prime]-O(3-thiotriphosphate), and GTP, did not increase channel activity in the membrane patches. Inward K+ channel activity in membrane patches preactivated by exogenous ATP was inhibited by glucose plus hexokinase. These results suggest that a low concentration of ATP is required for activation of the inward K+ channels of the guard-cell plasma membrane. The issue of how ATP as a signal regulates these K+ channels is discussed.
在体内，钾离子通过内向整流钾通道进入保卫细胞是由ATP通过使膜电位超极化的H⁺ - ATP酶间接驱动的。然而，保卫细胞钾通道的激活是否需要ATP仍然未知。在本研究中，采用全细胞和单通道膜片钳技术来解决这个问题。将外源ATP、ADP和腺苷 - 5'-O-(3-硫代三磷酸)施加到细胞质中，对蚕豆保卫细胞的全细胞钾电流没有影响。氧化磷酸化抑制剂叠氮化物也没有影响。然而，一个ATP清除系统，葡萄糖加己糖激酶，可使全细胞内向钾电流抑制30%至40%。从无细胞质的内向外膜片获得的单通道结果显示，ATP可明确激活内向钾通道。其他核苷酸，如ADP、腺苷 - 5'-O(3-硫代三磷酸)和GTP，不会增加膜片中的通道活性。外源ATP预激活的膜片中的内向钾通道活性被葡萄糖加己糖激酶抑制。这些结果表明，保卫细胞质膜内向钾通道的激活需要低浓度的ATP。文中讨论了ATP作为信号如何调节这些钾通道的问题。
