FREE-ION CONCENTRATIONS IN RECEPTOR LYMPH AND ROLE OF TRANSEPITHELIAL VOLTAGE IN THE FLY LABELLAR TASTE RECEPTOR

Free ion concentrations in the receptor lymph of the labellar taste hair were examined on the fleshfly Boettcherisca peregrina, making use of several kinds of ion-selective microelectrodes inserted into the outer lumen of the taste hair through its cut end. The receptor lymph was rich in Na+ and Cl- but poor in K+, that is, concentrations of Tree Na+, K+, Ca2+ and Cl- were (in mM) 117, 24, 0.2 and 109, respectively. The haemolymph of this insect had similar free ion concentrations. Next, the role of transepithelial voltage (TEV; 47.1 +/- 1.0 mV), which the receptor lymph space of the taste hair had with respect to the haemolymph, was examined. The quantitative relationship between the TEV amplitudes and the impulse frequencies of the sugar receptor evoked by sucrose stimulation was determined, changing TEV with application of respiratory inhibitors to the taste hair tip or by injecting current into the outer lumen. The TEV is concluded to provide the major component of the driving electromotive force for the receptor current to flow.