Stabilizing membrane domains antagonizes n-alcohol anesthesia

TL;DR

This study demonstrates that stabilizing membrane heterogeneity counteracts n-alcohol anesthesia, supporting the idea that membrane phase behavior influences anesthetic potency.

Contribution

It shows that agents raising membrane critical temperature oppose n-alcohol anesthesia, highlighting membrane heterogeneity as a key factor in anesthesia mechanisms.

Findings

Hexadecanol antagonizes ethanol-induced anesthesia.

Intoxication reversers raise membrane critical temperature.

Hydrostatic pressure counteracts butanol effects.

Abstract

Diverse molecules induce general anesthesia with potency strongly correlated both with their hydrophobicity and their effects on certain ion channels. We recently observed that several n-alcohol anesthetics inhibit heterogeneity in plasma membrane derived vesicles by lowering the critical temperature ($T_c$) for phase separation. Here we exploit conditions that stabilize membrane heterogeneity to further test the correlation between the anesthetic potency of n-alcohols and effects on $T_c$. First we show that hexadecanol acts oppositely to n-alcohol anesthetics on membrane mixing and antagonizes ethanol induced anesthesia in a tadpole behavioral assay. Second, we show that two previously described `intoxication reversers' raise $T_c$ and counter ethanol's effects in vesicles, mimicking the findings of previous electrophysiological and behavioral measurements. Third, we find that hydrostatic pressure, long known to reverse anesthesia, also raises $T_c$ in vesicles with a magnitude that counters the effect of butanol at relevant concentrations and pressures. Taken together, these results demonstrate that $\Delta T_c$ predicts anesthetic potency for n-alcohols better than hydrophobicity in a range of contexts, supporting a mechanistic role for membrane heterogeneity in general anesthesia.