Sensory irritant receptor compartment properties. Equipotent vapour concentrations related to saturated vapour concentrations, octanol-water, and octanol-gas partition coefficients.

Receptor compartments can be hydrophilic or hydrophobic. The hydrophobic character can be revealed from the logarithmic relationship between the octanol-water partition coefficient (Po/w) and the equipotent equilibrium concentration (Cw) measured in the water compartment (Franke: Theoretical Drug Design Methods. Elsevier, Amsterdam 1984). For activation of the sensory irritant receptor during exposure to airborne chemicals the Cw values at equilibrium can be obtained from the gas or vapour concentrations [( A]a) and the water-gas partition coefficients (Pw/g). However, if the octanol-gas partition coefficients (Po/g) are used, the analysis can be carried out directly from the gas or vapour concentrations. The thermodynamic activity can also be used to reveal whether the environment of the receptor is hydrophobic or not. We have adapted Franke's theory to a series of homologous airborne sensory irritants. Our results suggest that the environment of the sensory irritant receptor is likely to be a hydrophobic site within the polar part of the nerve membrane. The extended theory is general and it is therefore suggested that it applies to other airborne exposure concentrations which are in equilibrium with a hydrophobic receptor.