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.