Inhibitors of sensillar esterase block reversibly the responses of moth pheromone receptor cells

The pheromone of Antherae polyphemus is slowly (within min) degraded by a sensillum lymph specific esterase. The effects of two volatile alkyl-thio-trifluoro-methyl-ketones with alkyl chain length of six (HTFP) and ten carbons (DTFP), which selectively inhibit the activity of the sensillar esterase, were tested. Single sensillum recordings from sensilla trichodea were performed on isolated antennae either held in a continuous stream of clean air, or exposed to an airstream containing one of the esterase inhibitors. Afterwards the antennae were stimulated with the pheromone components (E,Z)-6,11-hexadecadienyl acetate and (E,Z)-6,11-hexadecadienal. Both esterase inhibitors caused a reduction of electrophysiological responses to each of the two pheromone compounds. The DTFP was slightly more effective than HTFP. An almost complete block of the receptor potential amplitude and nerve impulse response was achieved within seconds of exposure to the inhibitors. Responses of both pheromone receptor cells were reduced to the same extent. The half-times of rise and decline of the receptor potential remained unaffected in most cells. The responses to pheromone partially recovered to approximately 50-70% within several min in clean air. An inhibition of the sensillar esterase cannot explain the observed effects. The inhibitors could either react directly with the receptor molecules, thereby inhibiting the action of the pheromone, or bind to the pheromone-binding protein (PBP) and prevent the formation of the pheromone-PBP complex stimulating the receptor.