Na+ modulates the K+ permeability and the membrane potential of alkalophilic Bacillus.
In the absence of Na+ in the medium, the membrane potential of obligately alkalophilic Bacillus cells was found to be decreased by the addition of K+ to the medium, whereas K+ addition in the presence of Na+ had no effect. Rb+ showed essentially the same effect as K+. The decreased membrane potential was quickly restored by lowering the K+ concentration in the medium or by adding Na+ or Li+ to the medium. Thus, in the absence of Na+, the membrane potential of alkalophilic Bacillus seems to be affected by the concentration difference of K+ between inside and outside of the cell, and Na+ or Li+ in the medium suppresses the K+ effect. An exchange between extracellular Rb+ and intracellular K+ was observed in the absence of Na+. However, the exchange was greatly suppressed by the addition of Na+ or Li+ to the medium, indicating that Na+ in the medium modulates the K+ permeability of the alkalophilic Bacillus cell membrane. The K+-induced decrease in the membrane potential of alkalophilic Bacillus in the absence of Na+ is accounted for by the increased K+-permeability of the cell membrane.
Matsukura
H
H
Department of Molecular Biology, Faculty of Science, Nagoya University, Japan.
Imae
Y
Y
D001407:Bacillus / Q000502:physiology*; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology*; D002463:Cell Membrane Permeability; D006863:Hydrogen-Ion Concentration; D008564:Membrane Potentials / Q000187:drug effects; D011188:Potassium / Q000378:metabolism* / Q000494:pharmacology; D012964:Sodium / Q000494:pharmacology*; D014634:Valinomycin / Q000494:pharmacology
D014634:Valinomycin; D012964:Sodium; D011188:Potassium