VANADATE SELECTIVELY INHIBITS THE K-0(+)ACTIVATED NA+ EFFLUX IN SQUID AXONS

The effects of internally applied 1 mM vanadate on the Na+ efflux in dialysed squid axons were found to depend on the presence of external K+. In K+-free artificial sea water, vanadate did not produce any change in the rate of Na+ efflux, whereas in the presence of 10 mM K+ the Na+ efflux was reduced to values even lower than those observed in the absence of K+ (inversion of the K+-free effect). In vanadate-poisoned axons, K+ and NH4+ at low concentrations activated Na+ efflux, but at high concentrations both cations were inhibitory. However, NH4+ was always a better activator and a poorer inhibitor than K+. © 1979.