Light‐dependent Δ\̄smNa‐generation and utilization in the marine cyanobacterium Oscillatoria brevis

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Abstract
Light‐dependent Na+ and H+ transports, membrane potential (Δψ) and motility have been studied in the cells of the marine cyanobacterium Oscillatoria brevis. In the presence of a protonophorous uncoupler, carbonyl cyanide‐m‐chlorophenylhydrazone, the intracellular Na+ level is shown to increase in the dark and decrease in the light. The Na+/H+ antiporter, monensin, stimulates the dark CCCP‐dependent [Na+]in increase and abolishes the light‐dependent [Na+]in decrease. Na+ ions are necessary for the fast light‐induced Δψ generation and H+ uptake by the cells. This uptake is inhibited by monensin being resistant to CCCP. Monensin sensitizes the Δψ level and the motility rate to low CCCP concentrations. The obtained data are consistent with the assumption that O. brevis possesses a primary Na+ pump which utilizes (directly or indirectly) the light energy.