Fig. 3. Fusion of the TRPL channel to eGFP did not affect the physiological properties of the channel in vivo and in situ. (A, upper) ERG recordings from wild-type (WT) flies in response to a pair of orange light stimuli (Schott OG 590 edge filter) with maximal intensity attenuated by 1.0 log unit. (A, middle) ERG recordings from transgenic Drosophila expressing TRPL-eGFP fusion protein on null trpl; trp background (yw trpl-eGFP; trpl³⁰²; trp^P343) in response to the same pair of orange light stimuli used for trace A (upper). There is a transient receptor potential, which declines to baseline within 5 seconds. This light response is typical for trp mutants and it is expected from light activation of TRPL channels without the presence of TRP channels. An unusual large response to the second light stimulus after a 10-second dark interval can be observed. (A, bottom) ERG recordings from the null trp mutant (yw;; trp^P343) in a paradigm identical to that of the traces in A (upper and middle). (B) Intensity-response relationship (V-log I curve) measured from WT and the two mutants of Fig. 2A. The peak ERG amplitude was measured as a function of the orange light intensities. The error bars indicate ± s.d. (n=9). (C) The peak amplitude of the response to the second stimulus (see traces A middle and bottom) was divided by the peak amplitude of the response to the first stimulus and the averaged ratio calculated from six flies per mutant is presented for the trpl-eGFP and trp^P343 mutants. One minute of dark adaptation was used between the pairs of stimuli. (D) The light-induced currents at different membrane potentials are similar in both the TRPL-eGFP-expressing fly and the null trp mutant. Whole-cell patch-clamp recordings from isolated ommatidium of yw trpl-eGFP; trpl³⁰²; trp^P343 fly. Voltage clamp responses to identical orange light pulse of 100 milliseconds duration (Schott OG 590 edge filter with maximal intensity attenuated by 1.0 log unit) delivered at the time indicated by the arrow. The photoreceptor was voltage clamped at membrane potentials between -120 mV and +80 mV in steps of 20 mV. A reversal potential of -1 mV was determined by interpolation after plotting the peak amplitude of the light-induced current as a function of the membrane potential. Very similar reversal potential and similar strongly outward rectifying current voltage relationship was reported for the trp mutant (Hardie and Minke, 1992).