Coupling and Selectivity of Sodium and Potassium Transport in Squid Giant Axons

O u r purpose in this paper is to present some experimental findings that have a bear ing on the t ransport of sodium a nd potassium across the m e m b r a n e of the squid giant axon. As in a variety of cellular types that actively t ranspor t sodium ions, a marked drop in the efflux of sodium ions from squid g iant axons occurs when potassium ions are removed from the external solution (CaldweU et al., 1960). As both sodium exit and potassium entry are susceptible to inhibi t ion by appl icat ion of cyanide and other metabol ic inhibitors, the implicat ion is tha t some form of coupling exists between K influx and Na efltux. CaldweU et al. (1960) observed that inject ion of arginine phosphate into cyanide-poisoned axons restored the coupling between K entry and Na exit. I n the experiments described here, a n a t tempt was made to vary the inside concentra t ion of sodium ions in squid giant axons a nd the outside concentra t ion of potassium and potassium-like ions ( R b + and Cs +) in order to study the influence of such variat ions on the coupled t ransport of sodium a nd potassium ions.