Wing (Ib) cells in frog taste discs detect dietary unsaturated fatty acids

The effects of unsaturated fatty acids on membrane properties were studied using conventional whole-cell patch-clamp recording of isolated wing (Ib) cells in bullfrog (Lithobates catesbeianus) taste discs. Applying arachidonic acid to the bath induced monophasic inward currents in 60% of wing cells and biphasic inward and outward currents in the other cells. The intracellular dialysis of arachidonic acid did not induce an inward current; however, it enhanced a slowly developing Ba2 +-sensitive outward current. The effects of various unsaturated fatty acids were explored under the condition of Cs+ internal solution. Linoleic and α-linolenic acids induced large inward currents. Oleic, eicosapentaenoic and docosahexaenoic acids elicited the same inward currents as those of arachidonic acid. Wing cells, under the basal condition with Cs+ internal solution, displayed a small inward current of − 1.1 ± 0.1 pA/pF at − 50 mV (n = 40), in which the peak existed at a membrane potential of − 49 mV. Removing external Ca2 + further increased the inward current by − 2.9 ± 0.3 pA/pF at − 50 mV (n = 4) from the basal current and the peak was located at − 55 mV. External linoleic acid (50 μM) also induced a similar inward current of − 5.6 ± 0.6 pA/pF at − 50 mV (n = 19) from the basal current and the peak was located at − 61 mV. External Ca2 +-free saline and linoleic acid induced similar current/voltage (I/V) relationships elicited by a ramp voltage as well as voltage steps. Linoleic acid-induced currents were not influenced by replacing internal EGTA with BAPTA, whereas inward currents disappeared under the elimination of external Na+ and addition of flufenamic acid. These results suggest that dietary unsaturated fatty acids may depolarize wing (Ib) cells, which affects the excitability of these cells.