KILLING K-CHANNELS WITH TEA(+)

Tetraethylammonium (TEA(+)) is widely used for reversible blockade of K channels in many preparations, We noticed that intracellular perfusi on of voltage-clamped squid giant axons with a solution containing Kand 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 greater than or equal to 10 mM K+ to the e xtracellular solution. The rate of disappearance of K channels followe d 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(+) derivati ve 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+ interna lly 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+. T hus in the absence of extracellular K+, application of TEA(+) (or C10( +)) has effects resembling dekalification and kills the K channels.