Incorporation of 3 H-labelled leucine into the protein fraction in the retina of the honeybee drone

Immunocytochemical localization of photopigments in cephalopod retinae

The photopigments, rhodopsin and retinochrome, have been localized in cephalopod retinae using light and electron microscopic immunocytochemical methods. Polyclonal antibodies prepared against squid opsin demonstrated the presence of this protein in the photoreceptor rhabdomes, Golgi zone, Golgi-associated vesicles, plasma membrane, large cytoplasmic vesicles, and axonal membranes of octopus retinae. Monoclonal anti-opsin immunostained the rhabdomes and multivesicular bodies in the photoreceptor inner segments of squid. We believe the multivesicular bodies are involved in rhabdome turnover. Polyclonal anti-retinochrome localized this photopigment to the myeloid bodies of the photoreceptor inner segments, the rhabdomes, and to the extracellular space between opposing rhabdomeres in octopus retina. The results suggest some interesting functional relationships between rhodopsin and retinochrome with regard to chromophore exchange between illuminated forms of these photopigments and chromophore addition to newly synthesized opsin.

Autoradiographic and biochemical analysis of photoreceptor membrane renewal in Octopus retina

Using autoradiographic and biochemical methods, we have demonstrated the renewal of light-sensitive membranes and photopigments in Octopus visual cells. After the injection of Octopus with [3H]leucine, electron microscope autoradiography revealed an intracellular pathway similar to that in vertebrates for the synthesis and transport of nascent protein from the inner segments to the rhabdomes. However, migration of labelled protein from synthetic sites to the light-sensitive rhabdomes took longer in Octopus than the equivalent process in vertebrates. Biochemical analysis of [3H]leucine-labelled retinas identified some of the labelled protein observed in autoradiographs of the rhabdomes as the visual pigment, rhodopsin. We have shown that retinochrome, a second photopigment in cephalopod retinas, is also renewed. Biochemical analysis 8 h after injection of [3H]leucine revealed heavy labelling of this photoprotein. Light microscope autoradiography of Octopus retina 8 h after injection of [3H]retinol showed labelling of both the rhabdomes and the myeloid bodies of the inner segments. Biochemical data gathered 8 h after injection of [3H]retinol indicated chromophore addition to both rhodopsin and retinochrome with retinochrome being more heavily labelled than rhodopsin. Thus, silver grains observed over the rhabdomes and inner segments could arise from one or both photopigments. These data suggest that retinal is stored in the myeloid bodies of the photoreceptor inner segments. Retinal could then be transferred, perhaps via retinochrome, to newly synthesized opsin before the visual pigment is assembled into new rhabdomeric membranes. Alternatively, retinochrome may serve to transport retinal from the myeloid bodies to the rhabdomes to regenerate rhodopsin as previously proposed.

Diffusion and consumption of oxygen in the superfused retina of the drone (Apis mellifera) in darkness

Double-barreled O2 microelectrodes were used to study O2 diffusion and consumption in the superfused drone (Apis mellifera) retina in darkness at 22 degrees C. Po2 was measured at different sites in the bath and retinas. It was found that diffusion was essentially in one dimension and that the rate of O2 consumption (Q) was practically constant (on the macroscale) down to Po2 s less than 20 mm Hg, a situation that greatly simplified the analysis. The value obtained for Q was 18 +/- 0.7 (SEM) microliter O2/cm3 tissue . min (n = 10), and Krogh's permeation coefficient (alpha D) was 3.24 +/- 0.18 (SEM) X 10(-5) ml O1/min . atm . cm (n = 10). Calculations indicate that only a small fraction of this Q in darkness is necessary for the energy requirements of the sodium pump. the diffusion coefficient (D) in the retina was measured by abruptly cutting off diffusion from the bath and analyzing the time-course of the fall in Po2 at the surface of the tissue. The mean value of D was 1.03 +/- 0.08 (SEM) X 10(-5) cm2/s (n = 10). From alpha D and D, the solubility coefficient alpha was calculated to be 54 +/- 4.0 (SEM) microliter O2 STP/cm3 . atm (n = 10), approximately 1.8 times that for water.

Does visual deprivation in adult animals affect macromolecular metabolism in visual neurons?

Two-wave-length visible cytospectrophotometry of gallocyanin-stained sections has shown that 30-day-long visual deprivation in adult rats results in an augmentation of RNA content per cell in the neurons of all cell layers in visual cortex. Light stimulation which in normally reared rats brought about an accumulation of RNA in visual cortex neurons gave rise in light-deprived animals to a disappearance of the deprivation-induced increase of neuronal RNA content. In retina ganglion neurons, RNA content per cell was not changed after the visual deprivation as well as after the illumination of the deprived rats although in normal animals this stimulation evoked an increase of RNA content in the retina neurons. The conclusion is made about marked alterations in macromolecular metabolism induced by a long-term hypoactivity in central and peripheral visual neurons of adult animals.

The distribution of 3H-leucine labeled protein in the retinula cells of the crayfish retina

The synthesis and distribution of 3H-leucine labeled protein was studied under conditions of diurnal lighting in the retinula cells of the crayfish retina with both light and electron microscopic autoradiography. Times ranging from two minutes to seven days after an intracardiac injection were analyzed. Quantification of the electron microscopic autoradiograms revealed that labeling of the cytoplasm was greater than the rhabdome at 2, 5, and 30 minutes and reached a peak at 12 hours. The rhabdome showed increasing activity after 5, 30, and 60 minutes, also reaching a peak at 12 hours. Radioactive label in cytoplasmic multivesicular bodies was higher than activity measured in either the total cytoplasm or rhabdome at all times except two minutes. Two temporally different microvillar labeling patterns were seen under diurnal lighting conditions. (1) Microvilli forming the slightly enlarged distal tip of the rhabdome retained their radioactivity at 1, 3, and 7 days, when labeling of the rest of the rhabdome microvilli was decreasing. (2) In the remainder of the microvilli, labeling at 1 and 12 hours appeared as a gradient which declined toward the proximal end of the rhabdome. This gradient subsequently reversed itself, showing heavier proximal labeling at three days. In a second experiment, labeling patterns in light and dark adapted rhabdomes were compared. In the dark, a distinct gradient of activity was observed with radioactivity concentrated distally and declining toward the proximal end of the rhabdome. A more even distribution of label was present in the light adapted eye, but a slight distal-proximal gradient was still present. The dark adapted rhabdomes had more radioactivity per unit area than those exposed to light.

Freeze-etch and histochemical evidence for cycling in crayfish photoreceptor membranes

Freeze-etched rhabdoms and adjacent cytoplasmic cytoplasmic organelles from crayfish compound eyes have been studied for evidence of photoreceptor membrane cycling. The protoplasmic leaflet face (PF) of split photoreceptor membrane of the microvilli is richly particulate. The particles (92 +/- 16 A in diameter in surface fractures; 70 +/- 9 A in cross fractures; density about 8000/mum2) probably indicate rhodopsin molecule localization. Closely similar particles appear in membranes of pinocytotic vesicles, multivesicular bodies (MVB) and secondary lysosomes. In contrast other retinular cell membranes like plasma membrane remote from the rhabdom are quite distinct (60 +/- 23 A particle diameter, density ca 1000/mum2.) Histochemical tests for acid phosphatase demonstrate its presence in well-developed (but not early stage) MVBs, mixed lamellar vesicular bodies (LVB) and lamellar bodies. Density of PF particles decreases from 8000 in MVB to roughly 4500/mum2 in LVB indicating a degradative sequence from rhabdom to lamellar bodies. Membrane leaflet orientations show that primary endocytosis from microvilli must be followed by secondary endocytosis of fused coated vesicles to form MVB. Morphological evidence for photoreceptor membrane resynthesis has not been found yet in crayfish but some has been obtained in other crustaceans.

Protein synthesis in the visual cells of the honeybee drone as studied with electron microscope radioautography

Protein synthesis was studied in the visual cells of an insect (honeybee drone, Apis mellifera) by electron microscope radioautography. After a single injection of tritiated leucine, the radioactivity first appears in the cytoplasm of the visual cell which contains ribosomes. Later, part of this radioactivity migrates to the rhabdome, the visual cell region which is specialized in light absorption. A maximal concentration of radioactivity is reached there 48 hr after the injection of leucine. This pattern of protein synthesis and transport resembles that described in vertebrate visual cells (rods and cones), where newly synthesized proteins have been shown to contribute to the renewal of the photoreceptor membrane.