Fig. 5. Functional expression of both classes of XORs. (A) Oocytes expressing a representative class I receptor (XB107) and (B) cells expressing a representative class II receptor (BX154) were stimulated with tetramarin fractions (water extract, upper traces), coffee aroma (middle traces) or frog-Ringer solution (lower traces). Cells expressing XB107 responded with a typical current upon stimulation with the water extract, but showed no response with coffee aroma (A). (B) Oocytes expressing a representative class II receptor (XB154) did not react to water extract, but showed a strong outward current upon stimulation with coffee aroma. Neither cell type responded to the control-stimulation with frog-Ringer solution (Ringer). In all cases current plots were done at a holding potential of +30mV; the times of stimuli are indicated by bars. Please note the different scaling in 5A and B.