Cation regulation in Anacystis nidulans

Anacystis nidulans accumulates K(+) in preference to Na(+). The majority of the internal K(+) exchanges with (42)K by a first order process at rates of about 1.3 pequiv·cm(-2)·sec(-1) in the light and 0.26 pequiv·cm(-2)·sec(-1) in the dark. Although the K(+)/K(+) exchange was stimulated by light and inhibited by 10(-4) M CCCP and 10(-5) M DCMU there are several indications that this cation is passively distributed in Anacystis. Inhibition of the exchange by CCCP and DCMU occurred at concentrations greater than those required to inhibit photosynthesis and the K(+) fluxes were stimulated by low temperatures. Moreover, although valinomycin stimulated the exchange this compound did not induce a net K(+) leak. Assuming K(+) is passively distributed and in free solution within the cytoplasm, as indicated by osmotic studies, would imply that there is an active Na(+) extrusion pump operating in this organism. As yet there are no firm conclusions about the nature of the energy source for this efflux pump.