  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.
