PLANT PHYSIOLOGY , Vol 107, Issue 1 101-109, Copyright © 1995 by American Society of Plant Biologists
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CELL BIOLOGY AND SIGNAL TRANSDUCTION |
Is ATP Required for K+ Channel Activation in Vicia Guard Cells?
W. H. Wu and S. M. Assmann
Department of Biology, The Pennsylvania State University, 208 Mueller Laboratory, University Park, Pennsylvania 16802
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.
