Residual bodies resulting from photosensory membrane degradation are taken up by pigment cells in the eyes of the flyLucilia sp.

Retinae of blowflies (Lucilia sp.) were exposed to light for 12 h and then investigated by routine electron microscopy. Residual bodies and multi-vesicular bodies containing electron-dense structures were found in the photoreceptor cells. These structures appeared indistinguishable from material inside the pigment granules of secondary pigment cells. The residual bodies were found in interdigitations between photoreceptor and pigment cells and were often in close contact with mitochondria. Lamellar bodies and pigment granules were also found in the extracellular space between photoreceptor and pigment cells. In a second set of experiments, a membrane-impermeable reagent [sulfosuccinimidyl-6-(biotinamido) hexanoate] that should covalently biotinylate the surface of the photosensory membrane was introduced into the ommatidial cavity. The marker was detected, 4 h after application, inside the ommatidial cavity, on the rhabdomeric microvilli, and on residual bodies inside the photoreceptor cells, by streptavidin-gold binding on ultrathin sections. After 6 h of exposure to the reagent, pigment granules of the adjacent pigment cells were also labeled. The results suggest that the photosensory membrane is taken up and degraded together with the marker. Residual bodies resulting from this degradative process may thus be transported into the pigment cells; eventually material originating from photosensory membrane degradation may then be involved in pigment granule synthesis.