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 Ba(2+)-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±0.1pA/pF at -50mV (n=40), in which the peak existed at a membrane potential of -49mV. Removing external Ca(2+) further increased the inward current by -2.9±0.3pA/pF at -50mV (n=4) from the basal current and the peak was located at -55mV. External linoleic acid (50μM) also induced a similar inward current of -5.6±0.6pA/pF at -50mV (n=19) from the basal current and the peak was located at -61mV. External Ca(2+)-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.