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D Bok

Publications and source records attributed to D Bok.

At least 109 records · Page 6Linked to original sources
PubMed1982

Immunocytochemical localization of the lens main intrinsic polypeptide (MIP26) in communicating junctions.

Plasma membranes of vertebrate lens fiber cells contain a major intrinsic polypeptide with an apparent molecular weight of 26,000 (MIP26). These plasma membranes are extremely rich in communicating junctions, and it has been suggested that MIP26 is a component of them. MIP26 was purified from cow lenses using preparative SDS gel electrophoresis followed by hydroxylapatite column chromatography. From gel electrophoresis patterns and aggregational properties it was concluded that the MIP26 preparation was homogeneous. The purified MIP26 was used to produce monospecific antibodies in rabbits as assessed by double immunodiffusion and crossed immunoelectrophoresis of purified MIP26 and solubilized lens plasma membranes against the antiserum. Indirect immunocytochemical studies were performed on open and closed lens plasma membrane vesicles by incubation in anti-MIP antiserum followed by ferritin-conjugated goat antirabbit IgG. The conjugate bound unequivocally to lens communicating junctions, indicating that MIP26 is a component of these structures.

Aquaporins↗
PubMed1980

Autoradiographic localization of serum retinol-binding protein receptors on the pigment epithelium of dystrophic rat retinas.

The density and distribution of the retinal pigment epithelium membrane receptor for serum retinol-binding protein (RBP) was compared in young rats (28 days postnatal) and adult rats (7.5 months postnatal) afflicted with retinal dystrophy. Following an intravascular injection of 125I-labeled RBP (125I-RBP) complexed with prealbumin, the binding of 125I-RBP was analyzed by quantitative autoradiographic methods. As the course of the disease progressed, the pigment epithelium of the dystrophic retina underwent regional modification. Some areas remained unchanged, whereas others were grossly altered by vascular infiltration or by attenuation due to reduction in cell number. The basal infoldings of the pigment epithelium in young and adult rats exhibited nearly identical binding densities for 125I-RBP when unmodified cells were compared. In areas of severe disruption, the blood-retinal barrier was compromised, and the labeled protein diffused readily into the the neural retina. The results imply that the RBP receptors persist on the surface of unmodified pigment epithelial cells in adult dystrophic retinas in spite of the decrease in demand for retinol that accompanies the loss of photoreceptors.

Animals↗
PubMed1979

Electron microscopic localization of [125I]alpha-bungarotoxin binding sites in the outer plexiform layer of the goldfish retina.

Light and electron microscope autoradiography were performed on goldfish (Carassius auratus) retinas incubated in [125I]labelled alpha-bungarotoxin. The toxin was bound preferentially to membrane receptors in the inner and outer plexiform layers. Binding was suppressed by 10(-5) M nicotine or 10(-5) M native alpha-bungarotoxin. Electron microscopic analysis of the outer plexiform layer (OPL) strongly suggested that alpha-bungarotoxin binding sites were located on small bipolar cell dendritic processes that invaginated rod and cone synaptic terminals, and on large bipolar cell dendritic processes more proximally situated in the OPL. Large horizontal cell processes in the OPL and horizontal cell processes that invaginated rod and cone synaptic terminals did not appear to be labelled.

Animals↗
PubMed1978

GABA-ergic pathways in the goldfish retina.

A high-affinity uptake mechanism for [3H]-gamma-aminobutyric acid (GABA) has been localized to type H1 cone horizontal cells and type Ab pyriform amacrine cells in the retina of the goldfish by light and electron microscopy autoradiography. By stimulating isolated retinas with colored lights during incubation we have been able to use [3H]-GABA uptake as a probe of light-evoked changes in membrane potential. All colors of lights increase and darkness decreases [3H]-GABA uptake by H1 cone horizontal cells. Our model of voltage dependence of GABA uptake predicts that all colors of light should hyperpolarize H1 cone horizontal cells and other investigators have shown by intracellular recording and dye-marking that type H1 cone horizontal cells hyperpolarize to all wavelengths of light. We have also obtained evidence that dark-induced depolarization of cone horizontal cells leads to release of GABA. Type Ab pyriform amacrine cells show maximal [3H]-GABA uptake in darkness and when exposed to green or blue lights, but red lights dramatically suppress uptake. We predict these neurons to be red-depolarizing, and recent intracellular recordings and dye-marking by Famiglietti et al. ('77) support our conclusions. Synaptic relations of apparently GABA-ergic neurons were investigated in the electron microscope. We propose type H1 cone horizontal cells to be both pre- and post-synaptic to red-sensitive cones and type Ab pyriform amacrine cells to be both pre- and post-synaptic to red-sensitive center-depolarizing bipolar cells.

Animals↗
PubMed1977

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.

Adaptation, Ocular↗
PubMed1976

A specific receptor for retinol binding protein as detected by the binding of human and bovine retinol binding protein to pigment epithelial cells.

By means of autoradiographic techniques the specific plasma carrier of retinol, namely retinol binding protein (RBP) in a radioactive form (retinol-125I.RBP), bound specifically in vivo to the choroidal surface of intact, isolated bovine pigment epithelial cells. The retinol-125I.RBP did not bind to the retinal surface of the pigment epithelial cells nor did not bind to photoreceptors. Retinol is normally provided to the retina from the blood via a specific complex formation with a receptor on the chordial surface of the pigment epithelial cells. Retinol metabolism might be deranged in some diseases through a defect in the pigment epithelial receptor for RBP.

Animals↗
PubMed1976

Rhodopsin in the rod outer segment plasma membrane.

Isolated frog retinas were incubated in vitro with a 4-h pulse of [3H]leucine, then chased for 32 h with a nonradioactive amino acid mixture. At the end of the incubation, light and electron microscope autoradiograms were prepared from some of the retinas. The autoradiograms revealed: (a) intense radioactivity in the basal disks of the rod outer segments, (b) diffuse label evenly distributed throughout the rod outer segments, and (c) a high concentration of label in the entire rod outer segment plasma membrane. Incubation under identical conditions, but with puromycin added, significantly inhibited the labeling of all of these components. To identify the labeled proteins, purified outer segments from the remaining retinas were analyzed biochemically by SDS disc gel electrophoresis and gel filtration chromatography. SDS gel electrophoresis showed that about 90% of the total rod outer segment radioactivity chromatographed coincident with visual pigment, suggesting that the radiolabeled protein in the plasma membrane is visual pigment. Gel filtration chromatography demonstrated that the radiolabeled protein co-chromatographed with rhodopsin rather than opsin, and that the newly synthesized visual pigment is both the basal disks and the plasma membrane is present in the native configuration.

Animals↗