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Biomedical subjects

A G Yee

Publications and source records attributed to A G Yee.

6 recordsLinked to original sources
PubMed1978

Clusters of intramembranous particles on cultured myotubes at sites that are highly sensitive to acetylcholine.

Electrophysiological and autoradiographic studies have shown that the distribution of acetylcholine (AcCho) receptors on uninnervated cultured chicken muscle cells is not uniform. Regions of high receptor density (hot spots 10--40 times more sensitive than surrounding areas are localized as discrete patches or clusters about 10 micrometer in diameter o myotube muscle membranes. Hot spots were also found on fusion-arrested mononucleated myoblasts. We have developed a method for freeze-fracturing monolayer cultures that allows the unambiguous reidentification of membrane patches previously assayed for ACCho sensitivity. The freeze-fractured membranes at physiologically defined hot spots contain aggregates of many (10--20) small clusters of large (10--19 nm in diameter) intramembranous particles. Clusters are found on both fracture faces, but the particle density is much greater on the protoplasmic (P) face than on the extracellular (E) face (about 2000/micrometer2 vs. 700/micrometer2). Some of the particles appear to be composed of five or six "subunits" arranged cylindrically around a central dark dot. Because the aggregates are present at sites of high AcCho sensitivity, it is likely that the intramembranous particles are in some way related to the AcCho receptor molecule.

Acetylcholine↗
PubMed1978

Loss and reappearance of gap junctions in regenerating liver.

Changes in intercellular junctional morphology associated with rat liver regeneration were examined in a freeze-fracture study. After a two-thirds partial hepatectomy, both gap junctions and zonulae occludentes were drastically altered. Between 0 and 20 h after partial hepatectomy, the junctions appeared virtually unchanged. 28 h after partial hepatectomy, however, the large gap junctions usually located close to the bile canaliculi and the small gap junctions enmeshed within the strands of the zonulae occudentes completely disappeared. Although the zonulae occludentes bordering the bile canaliculi apparently remained intact, numerous strands could now be found oriented perpendicular to the canaliculi. In some instances, the membrane outside the canaliculi was extensively filled with isolated junctional strands, often forming very complex configurations. About 40 h after partial hepatectomy, very many small gap junctions reappeared in close association with the zonulae occludentes. Subsequently, gap junctions increased in size and decreased in number until about 48 h after partial hepatectomy when gap junctions were indistinguishable in size and number from those of control animals. The zonulae occludentes were again predominantly located around the canalicular margins. These studies provide further evidence for the growth of gap junctions by the accretion of particles and of small gap junctions to form large maculae.

Animals↗
PubMed1975

Endothelial cell junctions.

In the course of a freeze-cleave study on intercellular junctions in the regenerating rat liver, we observed an unusual array of intramembranous particles located in regions of contact between endothelial cells lining the hepatic sinusoids. These arrays were characterized by an accumulation of particles which resembled a zonula occludens in their linear deployment but differed in that the contact regions were composed of individual particles which remained separated from each other by regular particle-free intervals.

Animals↗
PubMed1971

Gap junctions between electrotonically coupled cells in tissue culture and in brown fat.

Although circumstantial evidence has suggested that gap junctions mediate intercellular electrotonic coupling, it has not been possible in most tissues to exclude the involvement of other, coexisting cell junctions. We have made an electron microscopic study of replicas of frozen-fractured BHK21 cells (from tissue culture) and of brown fat cells of newborn mice. Both of these cell types are known to exhibit intercellular electrical coupling. In each case, the only junctions found between the cells are small macular gap junctions (less than 1 mum in diameter) characterized by clusters of 6-nm (60 A) particles or depressions on membrane cleavage faces. Several replicas confirm the association of these particles and depressions with regions of narrowing of the intercellular space, i.e., with the sites of cell junctions. We have also determined the frequency of occurrence of gap junctions on the membrane cleavage faces of both cell types. Gap junctions occupy about 1-2% of the surface area of brown fat cells, but only 0.05% of the surface area of BHK21 cells. These observations indicate that gap junctions, when they are the only intercellular junctions present, are sufficient to account for electronic coupling between cells.

Adipose Tissue, Brown↗