Observations concerning the nature of sites of anaesthetic action in Gammarus.

We report the effects of n-alkanols (n-butanol to n-octanol), methyl carboxylic esters (methyl propionate to methyl octanoate) and n-alkyl ketones (2-pentanone to 2-nonanone) on a fast reflex escape response to a mechanical stimulus in Gammarus. ED50 concentrations and the relationships between In ED50 and chain length are given for each compound and series. For the n-alkanols, this relationship is well fit by a straight line (r2 = 1.000), with no evidence for a plateau between hexanol and heptanol. The standard free energy of transfer of a methylene group from water to a site of action in Gammarus is given for each series. The value for the esters is significantly smaller than that for the n-alkanols and ketones. These free energies are compared with those from other model systems, with the conclusion that further investigation of the differences between n-alkanols and esters will increase our understanding of the physico-chemical nature of the site(s) of action of general anaesthetics.