The effect of some general anaesthetics on the surface potential of lipid monolayers

1 This study sought to investigate the report by Ginsberg (1978) that 0.7 M ethanol brought about a + 100 mV change (DeltaDeltaV) in the surface potential of glyceryl monooleate (GMO) monolayers formed on KCl, although he predicted that a DeltaDeltaV of -10 mV should have been found.2 The effect of general anaesthetics such as n-alkyl alcohols and pentobarbitone on surface potential (DeltaV) and surface tension (gamma) of lipid monolayers formed on 145 mM KCl from either glyceryl monooleate (GMO) or phosphatidyl choline (PC) was examined with an Americium-241 air electrode assembly (DeltaV) and a platinized platinum dipping plate and force balance (gamma).3 It was found that, as predicted by Ginsberg (1978), addition of 0.7 M ethanol to the aqueous phase bathing either PC or GMO monolayers brings about a negative-going change in interfacial potential (DeltaDeltaV).4 The magnitude of DeltaDeltaV is dependent in a linear fashion on ethanol concentration.5 Longer chain length alcohols up to n-decanol also bring about a negative going change in DeltaDeltaV, and the dependence of DeltaDeltaV on anaesthetic activity, with respect to increasing chain length of anaesthetic, is consistent with Traube's law.6 Pentobarbitone added to the aqueous phase bathing the monolayer also elicits a negative DeltaDeltaV, a finding which rules out the possibility of adsorption of the volatile alcohols to the measuring electrode.7 The findings are discussed in terms of the proposition that increasing disorder in an array of fixed dipoles, such as might occur in a bilayer exposed to anaesthetic, would result in a lowering of the electrostatic barrier to the predominantly impermeable cation.