Interference of Injected Tetra-n-Propyl-ammonium Bromide with Outward Sodium Ion Current in Squid Giant Axons

Abstract

IT was demonstrated recently¹ that tetraethylammonium (TEA⁺) chloride affects the potassium permeability of a squid giant axon in a very interesting way. After TEA⁺ is injected into the axon to an axoplasmic concentration of about 40 mM, membrane resistance to outward K⁺ current is unusually high, while resistance to inward current remains about normal; that is, after injection the K⁺ permeable membrane has the property of “anomalous rectification”. This was interpreted to mean that TEA⁺ ions enter the membrane from the axoplasm and stop up the K⁺ channels unless the channels are swept clear of TEA⁺ by inrushing K⁺ ions. While testing other quaternary ammonium salts for this property, it was found that tetra-n-propylammonium (Tn-PA⁺) bromide affected in this way not only the K⁺ current but also the Na⁺ current.