Rapid interaction of tetraethylammonium with delayed K+ channel in mammalian brain neuron

In order to study the rapidity of interaction between tetraethylammonium (TEA) and the delayed K+ channel of the mammalian brain neuron, TEA was applied to isolated rat hippocampal pyramidal neurons in a time-controlled sequence with a voltage step using a concentration clamp technique. TEA at a concentration of 30 mM, externally applied, started to decrease the delayed K+ current (IKD) without any detectable delay after the onset of the drug application. The inhibitory action of TEA reached a steady state within 10 ms while the full recovery from the inhibition required 20-30 ms after removing TEA from the external solution. Ba2+ at a concentration of 30 mM also reduced the IKD without any detectable delay. However, it took 40-60 s to reach the steady state of inhibition. Full recovery from the inhibition by Ba2+ was obtained around 60 s after removal of Ba2+ from the external solution. It is suggested that the interaction of TEA with the delayed K+ channel is much faster than that of Ba2+.