Inhalational anaesthetics and n-alcohols share a site of action in the neuronal Shaw2 Kv channel

Background and purpose:

Neuronal ion channels are key targets of general anaesthetics and alcohol, and binding of these drugs to pre-existing and relatively specific sites is thought to alter channel gating. However, the underlying molecular mechanisms of this action are still poorly understood. Here, we investigated the neuronal Shaw2 voltage-gated K⁺ (K_v) channel to ask whether the inhalational anaesthetic halothane and n-alcohols share a binding site near the activation gate of the channel.

Experimental approach:

Focusing on activation gate mutations that affect channel modulation by n-alcohols, we investigated n-alcohol-sensitive and n-alcohol-resistant K_v channels heterologously expressed in Xenopus oocytes to probe the functional modulation by externally applied halothane using two-electrode voltage clamping and a gas-tight perfusion system.

Key results:

Shaw2 K_v channels are reversibly inhibited by halothane in a dose-dependent and saturable manner (K_0.5= 400 µM; n_H= 1.2). Also, discrete mutations in the channel''s S4S5 linker are sufficient to reduce or confer inhibition by halothane (Shaw2-T330L and K_v3.4-G371I/T378A respectively). Furthermore, a point mutation in the S6 segment of Shaw2 (P410A) converted the halothane-induced inhibition into halothane-induced potentiation. Lastly, the inhibition resulting from the co-application of n-butanol and halothane is consistent with the presence of overlapping binding sites for these drugs and weak binding cooperativity.

Conclusions and implications:

These observations strongly support a molecular model of a general anaesthetic binding site in the Shaw2 K_v channel. This site may involve the amphiphilic interface between the S4S5 linker and the S6 segment, which plays a pivotal role in K_v channel activation.