scholarly journals Quantitative analysis of low-resistance junctions between cultured cells and correlation with gap-junctional areas.

1978 ◽  
Vol 76 (2) ◽  
pp. 532-544 ◽  
Author(s):  
J D Sheridan ◽  
M Hammer-Wilson ◽  
D Preus ◽  
R G Johnson
Keyword(s):  
Cultured Cells ◽  
Freeze Fracture ◽  
Cell Populations ◽  
Novikoff Hepatoma ◽  
Low Resistance ◽  
Junctional Conductance ◽  
Electrophysiological Studies ◽  
The Mean ◽  
Gap Junctional ◽  
Isolated Cell

Electrophysiological studies of low-resistance junctions between Novikoff hepatoma cells grown in suspension cultures were carried out and correlated with gap-junctional areas per inferface determined by freeze-fracture. The mean coupling coefficient between isolated cell pairs was 0.773 +/- 0.025 (SEM) in 67G medium and 0.653 +/- 0.028 in M67 medium; the respective means for the central pairs of four-cell chains were 0.714 +/- 0.034 and 0.595 +/- 0.026. Mean estimates of nonjunctional resistances for cell pairs were 3.0 +/- 0.32 x 10(7) ohm (67G) and 2.01 +/- 0.01 x 10(7) ohm (M67), and the respective estimates for specific nonjunctional resistances were 158.6 +/- 8.1 ohm-cm2 (67G) and 133.0 +/- 812 ohm-cm2 (M67). Mean estimates of junctional conductances were 0.409 +/- 0.058 x 10(-6) mho (67G) and 0.211 +/- 0.018 x 10(-6) mho (M67) for pairs and 0.291 +/- 0.063 x 10(-6) mho (67G) and 0.212 +/- 0.04 mho (M67) for four-cell chains. The mean area of gap junction per interface for separate cell populations was 0.187 +/- 0.049 micron 2 and 0.269 +/- 0.054 micron 2 for cells fixed in loose pellets and in suspension, respectively. When compared with the mean junctional conductance, these values gave specific junctional conductance estimates of 1.13 x 10(2) mho/cm2 and 0.78 x 10(2) mho/cm2, respectively. These values are higher than most previous estimates, but are consistent with the hypothesis that gap-junctional particles contain central hydrophilic channels, about 2 nm in diameter, which have cytoplasmic resistivity.

Increased gap junction assembly between cultured cells upon cholesterol supplementation

1990 ◽  
Vol 96 (2) ◽  
pp. 231-238
Author(s):  
R. Meyer ◽  
B. Malewicz ◽  
W.J. Baumann ◽  
R.G. Johnson
Keyword(s):  
Gap Junction ◽  
Actinomycin D ◽  
Cultured Cells ◽  
Lucifer Yellow ◽  
Freeze Fracture ◽  
Cholesterol Content ◽  
Dye Transfer ◽  
Novikoff Hepatoma ◽  
Fourfold Increase ◽  
Cholesterol Supplementation

Novikoff hepatoma cells provide an excellent model system for the study of gap junction assembly, a process that could be influenced by lipids and other factors at numerous points. Since it is possible to alter the cellular levels of cholesterol in these cells, it was added to the cells in serum-supplemented medium and changes in gap junction assembly were evaluated. Cells were dissociated and reaggregated following exposure to a range of cholesterol concentrations for 24 h. A five- to sixfold increase in the number of aggregated gap junction particles and a 50% increase in cellular cholesterol content were observed with 20 microM added cholesterol. A 1-h exposure to added cholesterol, during cell reaggregation, resulted in a fourfold increase in the number of aggregated gap junction particles, demonstrating that the effect was rapid. The number of aggregated gap junction particles and formation plaque areas were used as measures of junction assembly and assayed by quantitative freeze-fracture and electron microscopy. Junctional permeabilities were evaluated by means of dye transfer times following the intracellular microinjection of Lucifer Yellow. Increased dye transfer was observed between cholesterol-treated cells, which suggested that the increase in assembly was accompanied by an increase in junction permeability. Cells were treated with cycloheximide (100 micrograms ml-1) and actinomycin D (10 micrograms ml-1) to determine whether protein and RNA syntheses were involved in the enhanced gap junction assembly. Cycloheximide but not actinomycin D blocked the increased junction assembly observed with added cholesterol. These results suggested that protein synthesis, but not RNA synthesis, is necessary for the increased gap junction formation observed.(ABSTRACT TRUNCATED AT 250 WORDS)

Freeze-Fracture Studies of Membranes in Developing Sieve Elements in a Plant Tissue Culture

1980 ◽  
Vol 38 ◽  
pp. 636-637
Author(s):  
R. D. Sjolund ◽  
C. Y. Shih
Keyword(s):  
Plant Tissue ◽  
Cultured Cells ◽  
Freeze Fracture ◽  
Tissue Cultures ◽  
Sieve Elements ◽  
Intact Plants ◽  
Plant Tissue Cultures ◽  
Whole Plants ◽  
Energy Dependent ◽  
Similar Elements

The differentiation of phloem in plant tissue cultures offers a unique opportunity to study the development and structure of sieve elements in a manner that avoids the injury responses associated with the processing of similar elements in intact plants. Short segments of sieve elements formed in tissue cultures can be fixed intact while the longer strands occuring in whole plants must be cut into shorter lengths before processing. While iyuch controversy surrounds the question of phloem function in tissue cultures , sieve elements formed in these cultured cells are structurally similar to those of Intact plants. We are particullarly Interested In the structure of the plasma membrane and the peripheral ER in these cells because of their possible role in the energy-dependent active transport of sucrose into the sieve elements.

Tetraethylammonium modifies gap junctions between pancreatic beta-cells

1981 ◽  
Vol 240 (3) ◽  
pp. C116-C120 ◽  
Author(s):  
M. S. Sheppard ◽  
P. Meda
Keyword(s):  
Beta Cell ◽  
Gap Junctions ◽  
Beta Cells ◽  
Insulin Release ◽  
Pancreatic Beta Cells ◽  
Freeze Fracture ◽  
Potassium Conductance ◽  
Median Number ◽  
Rat Islets Of Langerhans ◽  
Gap Junctional

Gap junctions between pancreatic beta-cells were quantitatively assessed in freeze-fracture replicas of isolated rat islets of Langerhans incubated for 90 min with or without the potassium conductance blocker tetraethylammonium (TEA). The results show that TEA increases the median number of particles per beta-cell gap junction but not the frequency of gap junctions at both nonstimulating and threshold-stimulating concentrations of glucose. TEA increased the relative gap junctional area at both concentrations of glucose. TEA had no effect on insulin release at a basal concentration of glucose but potentiated that release at the threshold glucose level. Thus TEA modifies beta-cell gap junctions independently of its effect on insulin release. However, the junctional changes observed were greater when insulin release was also elevated.

scholarly journals Arteriovenous Anastomoses in the Dermal Vasculatureof the Skin of Bos taurus Cattle, and their Relationship with Resistance to the Tick, Boophilus micro plus

1981 ◽  
Vol 34 (1) ◽  
pp. 27 ◽  
Author(s):  
AV Schleger ◽  
DT Lincoln ◽  
AS Bourne
Keyword(s):  
High Resistance ◽  
Bos Taurus ◽  
Neck Region ◽  
Skin Layer ◽  
Mean Value ◽  
Arteriovenous Anastomoses ◽  
Tick Feeding ◽  
Resistance Level ◽  
Low Resistance ◽  
The Mean

Bos taurus cattle with high resistance to the tick Boophilus micro plus, whether free-grazing or in covered pens, had significantly more arteriovenous anastomoses (A VA) in their skin than did animals of low resistance. These differences in number of A VA associated with resistance level were most marked above the level of the sebaceous gland in the neck region, an area favoured for tick feeding. In this skin layer, the number of AVA in low-resistance animals (4�0�0�4 per 2�1 mm) was significantly lower than in animals of high resistance (12�3 � 2�2 per 2�1 mm) while the mean value for the naive animals (8�2 � 1 �9 per 2�1 mm) was intermediate. No differences in morphology of AVA were detectable between the three groups using light microscopy.

Distinctive gap junction channel types connect WB cells, a clonal cell line derived from rat liver

1991 ◽  
Vol 260 (3) ◽  
pp. C513-C527 ◽  
Author(s):  
D. C. Spray ◽  
M. Chanson ◽  
A. P. Moreno ◽  
R. Dermietzel ◽  
P. Meda
Keyword(s):  
Gap Junction ◽  
Cell Line ◽  
Rat Liver ◽  
Connexin 43 ◽  
Single Channel ◽  
Freeze Fracture ◽  
Particle Sizes ◽  
Frequency Distributions ◽  
Gap Junction Channel ◽  
Junctional Conductance

Gap junctions, dye coupling, and junctional conductance were studied in a cell line (WB) that is derived from rat liver and displays a phenotype similar to “oval” cells. In freeze-fracture replicas, two distinctive particle sizes were detected in gap junctional plaques. Immunocytochemical studies indicated punctate staining at membrane appositions using antibodies to connexin 43 and to a brain gap junction-associated antigen (34 kDa). No staining was observed using antibodies prepared against rat liver gap junction proteins (connexins 32 and 26). Pairs of WB cells were electrically and dye coupled. Junctional conductance (gj) between cell pairs averaged approximately 10 nS; occasionally, gj was low enough that unitary junctional conductances (gamma j) could be detected. Using a CsCl-containing electrode solution, distinctive gamma j values were recorded: approximately 20-30 pS, approximately 80-90 pS, and the sum of the other sizes. The largest gamma j events were apparently due to random coincident openings or closures of the smaller channels. Several treatments reduced gj. Frequency distributions of gamma j were unaltered by 2 mM halothane or 3.5 heptanol, but the sizes of intermediate and largest events were reduced slightly by 100 nM phorbol ester, and the relative frequency of the largest events was increased by 10 microM glutaraldehyde. We conclude that the distinctive gamma j values represent openings and closures of two distinct types of gap junction channels rather than substates of a single channel type; these unitary conductances may correspond to the dual immunoreactivity and to the two particle sizes seen in freeze fracture.

scholarly journals Gap and Low-Resistance Junctions between Cells in Culture

1973 ◽  
Vol 28 (9-10) ◽  
pp. 603-606 ◽  
Author(s):  
Dieter F. Hülser ◽  
Anthony Demsey
Keyword(s):  
Gap Junctions ◽  
Freeze Fracture ◽  
Epithelioid Cells ◽  
Low Resistance ◽  
Cells In Culture

Abstract Established lines of both fibroblastoid and epithelioid cells have been investigated by electro-physiological and freeze-fracture methods. Between the ionically coupled (by "low-resistance junctions") fibroblastoid cells numerous gap junctions were found. Between the non-coupled epithelioid cells gap junctions could not be detected.

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