Biomedical subjects

A Dunina-Barkovskaya

Publications and source records attributed to A Dunina-Barkovskaya.

3 recordsLinked to original sources

PubMed1998

Tight junctions: facts and models.

Tight junctions (TJ) are specialized membrane structures found in cell-cell contact areas where the membranes of the neighbouring cells come into a close proximity. TJs have a characteristic ultrastructure on thin cross-section and freeze-fracture images and are regarded one of the diagnostic features of epithelial and endothelial cells where TJs form a transepithelial/transendothelial paracellular filter permeable for molecules of a certain size and also separate apical and basolateral domains of the plasma membrane of an epithelial cell. Two molecular models of TJs seek to explain structural and functional properties of TJs, a lipid model and a protein model. Due to the recent advances in biochemistry and molecular biology of TJs the protein model is most widely accepted. This review compares once again the ability of the two models to explain the phenomenology of TJs. The data on TJ ultrastructure and distribution are recalled here, including the data on TJs in fibroblastic cells where TJs appear fragmented or focal. TJ functions are considered, among which may be an intercellular communication due to cell-to-cell diffusion of lipophilic molecules. TJ modulators are listed and their activity in respect of the lipid phase transitions is noted. The major advantages and drawbacks of the two molecular models of TJs are discussed and a "synthetic" version of the lipid and protein models, reconciling the achievements of them both, is suggested.

Animals↗

PubMed1993

Biophysical characterization of gap-junction channels in HeLa cells.

HeLa cells seem not to be junctionally coupled when probed with techniques such as Lucifer yellow spreading and/or ionic coupling measured with three inserted microelectrodes. When investigated with double whole-cell patch-clamp measurements, HeLa cells in monolayer cultures were electrically coupled in 39% of the cases with very low transjunctional conductances (average one to five open channels). These gap-junction channels had a single-channel conductance gamma = 26 +/- 6 pS and were voltage-gated with an equivalent gating charge z = 3.1 +/- 1.5 for a voltage of half-maximal inactivation Uo = 49 +/- 10 mV. The voltage-dependent component represents only 31 +/- 8% of the total junctional conductance. The voltage-insensitive conductance is characterized by a residual open probability po (infinity) = 0.34 +/- 0.12, which corresponds to a ratio Gmin/Gmax = 0.50 +/- 0.12. Dissociation of monolayer cells into cell pairs yielded about 58% coupled cell pairs with no notably altered single-channel properties.

Connexins↗

PubMed1991

Hydrophobic ion transfer between membranes of adjacent hepatocytes: a possible probe of tight junction structure.

The topology of the tight junction is probed by introducing dipicrylamine (dpa-), a lipid-soluble anion, into the membranes of hepatocyte pairs in culture. Once partitioned into the membrane, dpa- ions are free to move in the hydrophobic core of the membrane, where their mobile charges greatly increase membrane capacitance. If tight junctions are lines of membrane fusion, dpa- will cross the tight junction without traversing a polar headgroup layer. Furthermore, the electric potential across the tight junction will be equal to the difference in membrane potentials of the two cells. dpa- can therefore be expected to move electrophoretically from cell membrane to cell membrane across the junction in response to an intercellular voltage difference. Experiments performed under double whole-cell clamp show that this transfer occurs as follows: First, dpa- causes an intercellular current unrelated to gap junctions to flow in response to an intercellular voltage difference. Second, this electrophoretic removal or addition of dpa- from a cell's membrane through the tight junction must reduce or increase its dpa- content and thus its capacitance. Experiments confirm this prediction: We detect rapid, symmetric, and reversible changes in membrane capacitance in response to changes in the membrane potential of the neighboring cell. Finally, we find that hepatocyte membranes contain a negatively charged endogenous molecule that contain a negatively charged endogenous molecule that can move from cell to cell like dpa- under the influence of an intercellular potential difference. We conclude that membrane fusion occurs at tight junctions and that this hydrophobic intercellular pathway can play a role in intercellular communication.

Animals↗