Sodium chloride stimulated respiration of Anacystis nidulans

With certain salts a stimulation of respiration of the blue-green alga Anacystis nidulans was found in the dark. The stimulation was observed only at high concentrations (10−2 M—10−1M). NaCl or LiCl are the most effective salts and on addition the increase of the respiration is about 2.5fold. Li is assumed to function as a substitute for Na. Potassium salts, except KCl, are ineffective. The order for the effectiveness is: NaCl > NaNO3, Na2SO4 > KCl > KNO3, K2SO4 (=zero). Accordingly, the cation Na+, and to a less degree the anion Cl are responsible for the stimulatory effect. K, which is ineffective, is passively accumulated by Anacystis according to the membrane potential. Na is actively extruded. At 0.1 M external NaCl, the passive influx of Na is high, but even then it is balanced by an active efflux. This increases the energy consumption of the cells and leads to a stimulated respiration. With DCCD (N,N′-dicyclohexylcarbodiimide) or NEM (N-ethylmaleimide), the Na efflux is inhibited, simultaneously the stimulation of respiration is abolished and the passive influx of Na becomes detectable. At 0.1 M NaCl, the passive influx of Na measured in presence of DCCD is 5 × 10−6 moles Na/min and ml packed cells. In absence of DCCD on addition of 0.1 M NaCl the extra oxygen consumption is 2 × 10−6 moles O2/min and ml cells. This may prove that the stimulation of respiration is mainly caused by the active Na extrusion.