Fig. 3. (A) The quantity of G_q translocated from the rhabdomere to the cell body is dependent on the intensity of illumination. Cross-sections of dark-raised wild-type flies were illuminated under the indicated light intensities for 1 hour. Sections were stained with anti-G_q antibody and quantified. Percentages of G_q remaining in the rhabdomeres after exposure to the indicated light intensities (I) were calculated, where initial light intensity (I₀)=70.0x10³ lumens meter^-2. Exposure to light intensities with log(I/I₀) of -5 to 0 resulted in translocation of 20-75% G_q out of the rhabdomeres. SEMs are indicated. (B) Photoisomerization of metarhodopsin to rhodopsin is required for G_q transport from the cell body to the rhabdomere. Shown are retinal cross-sections immunostained for G_q. Dark-raised wild-type flies were exposed to: (1) blue (bandpass 470 nm > > 490 nm) light for 2 hours; (2) blue light for 2 hours followed by 2 hours of orange (long-pass > 580 nm) light; or (3) blue light for 2 hours followed by 2.5 hours of dark incubation. Dark-raised flies showed normal, rhabdomeric localization of G_q whereas flies illuminated with blue light displayed translocation of G_q into the cell body. Flies exposed to blue light followed by orange light displayed almost full recovery of G_q to the rhabdomeres. Flies exposed to blue light followed by dark incubation showed no recovery of G_q to the rhabdomeres. These results indicate that photoisomerization of metarhodopsin to rhodopsin is absolutely required for normal translocation of G_q from the cell body to the rhabdomeres.