Killing K channels with TEA⁺

Tetraethylammonium (TEA⁺) is widely used for reversible blockade of K channels in many preparations. We noticed that intracellular perfusion of voltage-clamped squid giant axons with a solution containing K⁺ and TEA⁺ irreversibly decreased the potassium current when there was no K⁺ outside. Five minutes of perfusion with 20 mM TEA⁺, followed by removal of TEA⁺, reduced potassium current to <5% of its initial value. The irreversible disappearance of K channels with TEA⁺ could be prevented by addition of ≤ 10 mM K⁺ to the extracellular solution. The rate of disappearance of K channels followed first-order kinetics and was slowed by reducing the concentration of TEA⁺. Killing is much less evident when an axon is held at -110 mV to tightly close all of the channels. The longer-chain TEA⁺ derivative decyltriethylammonium (C10⁺) had irreversible effects similar to TEA⁺. External K⁺ also protected K channels against the irreversible action of C10⁺. It has been reported that removal of all K⁺ internally and externally (dekalification) can result in the disappearance of K channels, suggesting that binding of K⁺ within the pore is required to maintain function. Our evidence further suggests that the crucial location for K⁺ binding is external to the (internal) TEA⁺ site and that TEA⁺ prevents refilling of this location by intracellular K⁺. Thus in the absence of extracellular K⁺, application of TEA⁺ (or C10⁺) has effects resembling dekalification and kills the K channels.