The water taste transduction mechanism in the blowfly couplet aquaglyceroporins and strecth-sensitive channels

Aim: The gustatory system of the blowfly Protophormia terraenovae represents a relatively simple biological model for studies on chemosensory input and behavioral output. The water sensitive neuron ("water" cell) in the labellar chemoreceptors of the blowfly responds to increasing solute concentrations with decreasing spike firing frequency, except for glycerol and for fructose. To this end, we used a pharmacological approach to investigate the presence of water channels, aquaporins (AQPs) or aquaglyceroporins (AQglyPs), and their role in "water" cell excitability and the transduction mechanism involved. Methods: Aqueous solution of glycerol or fructose were tested on blowfly taste chemosensilla by way of the extracellular single sensillum recording technique, in the presence or absence of AQPs and stretch-sensitive channel inhibitors. Results: Our data show that the response of the "water" cell was strongly decreased by several AQP inhibitors such as HgCl2 and CuSO4 in a dose-dependent manner, while AgNO3, ACZ and TEA were ineffective. Besides, the "water" cell response was decreased by GdCl3, a stretch-sensitive channel blocker. Conclusions: Our data are consistent with the hypothesis of the existence of an AQP and/or AQglyPs at the chemoreceptor membrane level of the "water" cell in blowfly taste chemosensilla and also suggest a possible transduction mechanism mediated by a GdCl3-sensitive stretch-sensitive ion channel. The behavioural involvement is also discussed.