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Biomedical subjects

M Ohkuma

Publications and source records attributed to M Ohkuma.

At least 91 records · Page 5Linked to original sources
PubMed1981

Synaptic vesicle exocytosis in goldfish photoreceptor cells.

The photoreceptor cell endings of goldfish retinas were examined using ultrathin and freeze-fracture techniques. The synaptic vesicles could be seen lying closely packed in rows on each side of the synaptic ribbon, and the vesicles nearest to the end of the ribbon could be seen to be in direct contact with the presynaptic membrane. The openings of the synaptic vesicles to the synaptic cleft could also be observed at the presynaptic membrane nearest to the end of the ribbon, that is, 100 nm distant from the center of the apex. In the freeze-fractured replicas of the presynaptic membrane, the band-shaped membrane particle aggregation was seen at the apex and a row of the crater-like or circular protuberances were observed at each side of the apex. These structures were considered to be changes of the presynaptic membrane organizations according to the synaptic vesicle exocytosis. It may be possible that the synaptic vesicle exocytosis in the photoreceptor cells occurs at the sites of the presynaptic membrane nearest to the apical end of the synaptic ribbon, and that the exocytotic sites form a line on each side of the apex.

Animals↗
PubMed1980

Specialized intramembrane organizations of the cone presynaptic membrane in the pigeon retina. Freeze-fracture study.

The presynaptic membranes of the cone cell endings of the pigeon retina were investigated using the freeze-fracture technique. En face views of the cytoplasmic leaflet (P-face) of the split presynaptic membrane revealed several specialized membrane organizations, 1. membrane particle aggregates composed of 10-20 particles which were larger than the usual ones seen in the cell membrane, 2. fenestration-like circular structures of 30-50 nm in diameter which were not surrounded by membrane particles. 3. similiar circular structures as described above but which were accompanied by a few membrane particles on the circular margin and were considered to be an intermediate form of the first and second membrane structures. These three structures appeared simultaneously in one fracture plane of the presynaptic membrane; were situated at the same intervals from one another and were approximately equal in size to synaptic vesicles (30-50 nm). These findings strongly suggested that these three structures were serial events in presynaptic membrane organization. When fortuitous cross fractures exposed both the P-face of the presynaptic membrane and the adjacent cytoplasm of the cone ending, fusion of the synaptic vesicles to the presynaptic membrane was observed, and was considered to be the opening of the synaptic vesicle to the synaptic cleft. These openings were also situated at the same distance as the structures described above. These findings demonstrate the process of exocytosis of the synaptic vesicles by which the chemical transmitter is probably released to the synaptic cleft.

Animals↗
PubMed1978

Disruption of blood-retinal barrier at the retinal pigment epithelium after systemic urea injection.

Electron microscopic studies were done on the structural alterations of retinal pigment epithelial cells occurring under osmotic stress utilizing rhesus monkeys and lanthanum nitrate as a tracer. Fluorescein fundus angiography revealed leaking points of fluorescein from the choroid to the retina, and various degenerative alterations of the retinal pigment epithelial cells were observed in these leaking areas. Some cells included many vacuoles in their cytoplasm, but diffusion of lanthanum from the choroid to the outer segment of visual cell was obstructed by the tight junctions between the retinal pigment epithelial cells. Other cells were severely damaged with ruptured membranes. Abundant tracer material diffused through the cytoplasm into the subretinal space. Other cells were broken down in an isolated manner and here marked extravasation of lanthanum into the subretinal space was observed.

Animals↗
PubMed1977

Melanosomes of pigmented basal cell epithelioma.

Electron microscopic examination of a pigmented basal cell epithelioma of scrotal skin revealed many tumor cells and melanocytes which were laden with large packages of melanosomes. In tumor cells these packages were delimited by either single- or double-limiting membranes or were not membrane bound. The matrix of these large complexes was less electron dense and homogeneous than normal, containing electrontranslucent droplets besides melanosomes. No remnants of intracellular organelles such as nucleus, mitochondria or ribosomes could be found. The basal cell epithelioma cells in this case appear to have differentiated toward fetal basal cells and have developed the ability to phagocytize large packages of melanosomes.

Basal Cell Carcinoma↗