Na + modulates the K + permeability and the membrane potential of alkalophilic Bacillus

Abstract

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.