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Is ATP Required for K+ Channel Activation in Vicia Guard Cells?
by Wu W.-H., Assmann S. M. (1995)
in Plant Physiol 107:101–109. –
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.