A comparison of phenylalkyl- and phenoxyalkyl- trimethylammonium and triethylammonium salts; their apparent molal volumes at infinite dilution and effects on the frog rectus and guinea-pig ileum preparations.

1. The effects of phenoxyalkyltrimethylammonium and triethylammonium bromides on the frog rectus preparation and on the isolated guinea-pig ileum in the presence of hexamethonium have been compared with those of analogous phenylalkyltrimethylammonium and triethylammonium bromides. Affinity constants have been measured when possible.2. The apparent molal volumes at infinite dilution of some of the compounds have been measured from estimates of density made with an Anton Paar precision density meter.3. An ether oxygen occupies at infinite dilution in water only about one-third of the volume occupied by a methylene group.4. The replacement of methylene by ether oxygen reduces nicotine-like activity and affinity for nicotine-sensitive receptors. The reduction in affinity may be partly due to the decrease in size.5. The replacement of methylene by ether oxygen reduces activity and affinity at muscarine-sensitive receptors but in some compounds there is a bigger reduction in affinity than would be expected simply from the reduction in size.6. It is suggested that the affinity of these compounds largely depends on hydrophobic bonding and that effects on water structure in the environment of the receptor may also be involved in the actions of agonists.