Opening of Potassium Channels in Escherichia coli Membranes by Thiol Reagents and Recovery of Potassium Tightness

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Abstract
The retention of high K levels in E. coli is not dependent on intact energy metabolism, since without the presence of a C source or in the presence of energy inhibitors significant K+ gradients can be maintained. With 0.5 mM N-ethylmaleimide, K+ depletion is immediate and complete. As a final result, intracellular K+ is approximately 3 times more concentrated than the K+ in the medium. Increase of K+ in the medium is immediately followed by K+ uptake whereas in the unposioned state only an increase in the osmotic pressure of the medium would result in an increase of the K+ pool. The intracellular K+ undergoes continuous turnover in the poisoned cells whereas in intact cells turnover is strictly dependent on the presence of a metabolizable C source. After removal of the thiol reagent the cell recovers its capacity to concentrate K. The recovery process is inhibited by energy inhibitors or by incubation at low temperature but not by chloramphenicol. It is only slightly slowed down by C or S starvation. The leak provoked by N-ethylmaleimide is similar in wild-type E. coli cells when a derepressed kdp uptake system working in the micromolar range of the K+ concentration is responsible for the intracellular pool of K+ and when, in a medium of millimolar K+ concentration range, the trkA and trkD systems are predominant.

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