PLANT PHYSIOLOGY , Vol 105, Issue 3 927-935, Copyright © 1994 by American Society of Plant Biologists
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CELL BIOLOGY AND SIGNAL TRANSDUCTION |
Are Redox Reactions Involved in Regulation of K+ Channels in the Plasma Membrane of Limnobium stoloniferum Root Hairs?
A. Grabov and M. Bottger
Universitat Hamburg, Institut fur Allgemeine Botanik, Ohnhorstrasse 18, D-22609 Hamburg, Germany
The effects of the impermeant electron acceptor hexacyanoferrate III (HCF
III) and the potassium channel blocker tetraethylam-monium (TEA) on the
current-voltage relationship and electrical potential across the plasma
membrane of Limnobium stoloniferum root hairs was investigated using a
modified sucrose gap technique. One millimolar HCF III immediately and
reversibly depolarized the membrane by 27 mV, whereas the effect on the
trans-membrane current was markedly delayed. After 6 min of treatment with
this electron acceptor, outwardly rectifying current was inhibited by 50%,
whereas the inwardly rectifying current was activated approximately 3-fold.
Ten millimolar TEA blocked both outward (65%) and inward (52%) currents.
Differential TEA-sensitive current was shown to be blocked (55%) by HCF III
at -20 mV and was shown to be stimulated (230%) by this electron acceptor
at -200 mV. The inward current at -200 mV was eliminated in the absence of
K+ or after addition of 10 mM Cs+ and was not affected by addition of
either 10mM Na+ or Li+, independent of the presence of HCF III. The
addition of any alkali cation to the external medium decreased the outward
current both in the presence and in the absence of HCF III. The membrane
depolarization evoked by HCF III did not correlate with the corresponding
modification of the inward current. HCF III is proposed to activate
inwardly rectifying potassium channels and to inactivate outwardly
rectifying potassium channels. It is concluded that the plasma membrane
depolarization did not result from modulation of the potassium channels by
HCF III and may originate from trans-plasma membrane electron transfer.
