Potassium-free Effect in Squid Axons

PREVIOUS work 1 has shown that the sodium efflux from squid giant axons is sensitive to the external concentration of potassium ions; the Na efflux falls to about 1/3 of control values when the sea water surrounding the axon is made free from potassium. Similar observations have been made with frog sartorius muscle 2 , but these showed further that when [Na] i in muscle was low, Na efflux was no longer sensitive to external [K]. The following experiments were undertaken to see if the Na efflux from squid axons would be similarly insensitive to [K 0 ] if [Na] i were low.