Light and Electron Microscopic Studies Regarding Cell Contractility and Cell Coupling in Light Sensitive Smooth Muscle Cells from the Isolated Frog Iris Sphincter

1987 ◽  
Vol 42 (7-8) ◽  
pp. 977-985 ◽  
Author(s):  
Klaus V. Wolf
Keyword(s):  
Gap Junctions ◽  
Freeze Fracture ◽  
Muscle Cells ◽  
Sphincter Muscle ◽  
Cell Coupling ◽  
Electron Microscopic ◽  
Thin Sections ◽  
Cell Contractility ◽  
Microscopic Studies ◽  
Iris Sphincter

(1) In light microscopical studies of living isolated frog irises, it was found that the maximal areas of experimentally light induced contractions in the m. sphincter pupillae were located beneath small illuminated regions. There were no visible contractions of muscle cells outside the illuminated areas. It was shown that exposure to light could directly cause contractions of isolated single sphincter muscle cells. (2) Junctional structures of the iris sphincter cells were studied by means of thin sections and freeze fracture electron microscopy. Intermediate junctions, a few focal tight junctions and occasional small gap junctions were identified. Pit containing intramembranous particles which resemble gap junction connexons were found in large numbers, dispersed over the plasmalemmas of sphincter muscle cells. From these physiological and morphological observations, it is concluded that sphincter muscle cells of the frog iris may be coupled via gap junctions, but that the cell coupling is not sufficiently extensive to form the basis for a functional syncytium.

Calmodulin-mediated gating of lens gap junction channels in vesicles

1984 ◽  
Vol 42 ◽  
pp. 134-137
Author(s):  
Camillo Peracchia ◽  
Stephen J. Girsch
Keyword(s):  
Gap Junctions ◽  
Freeze Fracture ◽  
Orthogonal Arrays ◽  
Eye Lens ◽  
Lens Fiber ◽  
Cell Coupling ◽  
Particle Spacing ◽  
Fiber Cells ◽  
Gap Junction Channels ◽  
Communicating Junctions

The fiber cells of eye lens communicate directly with each other by exchanging ions, dyes and metabolites. In most tissues this type of communication (cell coupling) is mediated by gap junctions. In the lens, the fiber cells are extensively interconnected by junctions. However, lens junctions, although morphologically similar to gap junctions, differ from them in a number of structural, biochemical and immunological features. Like gap junctions, lens junctions are regions of close cell-to-cell apposition. Unlike gap junctions, however, the extracellular gap is apparently absent in lens junctions, such that their thickness is approximately 2 nm smaller than that of typical gap junctions (Fig. 1,c). In freeze-fracture replicas, the particles of control lens junctions are more loosely packed than those of typical gap junctions (Fig. 1,a) and crystallize, when exposed to uncoupling agents such as Ca++, or H+, into pseudo-hexagonal, rhombic (Fig. 1,b) and orthogonal arrays with a particle-to-particle spacing of 6.5 nm. Because of these differences, questions have been raised about the interpretation of the lens junctions as communicating junctions, in spite of the fact that they are the only junctions interlinking lens fiber cells.

Quantitative Freeze Fracture Studies of Gap Junctions in Somatic Cell Hybrids, Their Parents, and Revertants

1976 ◽  
Vol 34 ◽  
pp. 218-219
Author(s):  
W. J. Larsen ◽  
R. Azarnia ◽  
W. R. Loewenstein
Keyword(s):  
Gap Junctions ◽  
Striated Muscle ◽  
Freeze Fracture ◽  
Cell Movement ◽  
Dye Molecules ◽  
Somatic Cell Hybrids ◽  
Cell Coupling ◽  
Normal Cells ◽  
Mediate Cell ◽  
Almost All

Although the physiological significance of the gap junction remains unspecified, these membrane specializations are now recognized as common to almost all normal cells (excluding adult striated muscle and some nerve cells) and are found in organisms ranging from the coelenterates to man. Since it appears likely that these structures mediate the cell-to-cell movement of ions and small dye molecules in some electrical tissues, we undertook this study with the objective of determining whether gap junctions in inexcitable tissues also mediate cell-to-cell coupling.To test this hypothesis, a coupling, human Lesh-Nyhan (LN) cell was fused with a non-coupling, mouse cl-1D cell, and the hybrids, revertants, and parental cells were analysed for coupling with respect both to ions and fluorescein and for membrane junctions with the freeze fracture technique.

Gap junctions in the prothoracic glands of the tobacco hornworm, Manduca sexta

1992 ◽  
Vol 50 (1) ◽  
pp. 706-707
Author(s):  
Ji-da Dai ◽  
M. Joseph Costello ◽  
Lawrence I. Gilbert
Keyword(s):  
Gap Junctions ◽  
Small Molecules ◽  
Manduca Sexta ◽  
Freeze Fracture ◽  
Cell Communication ◽  
Cellular Level ◽  
Thin Sections ◽  
Prothoracic Glands ◽  
Polyhydroxylated Steroids ◽  
Stimulation Of

Insect molting and metamorphosis are elicited by a class of polyhydroxylated steroids, ecdysteroids, that originate in the prothoracic glands (PGs). Prothoracicotropic hormone stimulation of steroidogenesis by the PGs at the cellular level involves both calcium and cAMP. Cell-to-cell communication mediated by gap junctions may play a key role in regulating signal transduction by controlling the transmission of small molecules and ions between adjacent cells. This is the first report of gap junctions in the PGs, the evidence obtained by means of SEM, thin sections and freeze-fracture replicas.

Determinants of biliary secretion in isolated perfused skate liver

1982 ◽  
Vol 242 (4) ◽  
pp. G319-G325 ◽  
Author(s):  
J. S. Reed ◽  
N. D. Smith ◽  
J. L. Boyer
Keyword(s):  
Tight Junctions ◽  
Bile Flow ◽  
Perfusion Pressure ◽  
Freeze Fracture ◽  
Biliary Tree ◽  
Solute Diffusion ◽  
Electron Microscopic ◽  
Bile Formation ◽  
Ionic Lanthanum ◽  
Microscopic Studies

In the isolated perfused liver of the little skate, Raja erinacea, bile flow averaged 5.07 +/- 0.58 (mean +/- SE) microliters.h-1.g liver-1 in 21 experiments at a perfusion pressure of 5.0 cm Ringer compared to 3.79 +/- 0.32 in 38 experiments at 2.5 cm (P less than 0.05). [14C]inulin readily entered skate bile. Bile-to-plasma [14C]inulin ratios corrected for delay in transit time, averaged 0.46 +/- 0.07 at 1 h and rose to 0.74 +/- 0.06 by 4 h, although bile flow remained constant. In experiments in which [14C]inulin reached equilibrium between bile and plasma, the bile-to-plasma ratio conformed to the theoretical relationship between bile flow, solvent drag, and inert solute diffusion predicted at extremely low bile flows, but demonstrated that the skate biliary tree is more permeable to inulin than that of the rat. Electron microscopic studies demonstrated that ionic lanthanum could traverse the tight junctions. However, freeze-fracture studies of junction structure did not differ qualitatively from similar studies in the rat. Partial dependence of bile flow on perfusion pressure, high bile-to-plasma inulin ratios, and permeability of the canalicular tight junctions to ionic lanthanum all suggest that the paracellular pathway may be an important component of bile formation in the skate.

The syneretic lens junction

1984 ◽  
Vol 42 ◽  
pp. 16-19
Author(s):  
J. David Robertson ◽  
M.J. Costello ◽  
T.J. McIntosh
Keyword(s):  
Gap Junctions ◽  
Gap Junction ◽  
Cell Membranes ◽  
Freeze Fracture ◽  
Enzymatic Digestion ◽  
Fiber Cell ◽  
Intermembrane Space ◽  
Minor Components ◽  
Thin Sections ◽  
Fiber Cells

The lens of the eye consists of closely adherent greatly elongated flattened narrow fiber cells that are electrically coupled by gap junctions. In thin sections the 100-150 Å intermembrane space usually seen in tissues between adjacent cells is greatly reduced between adjacent fiber cells. Freeze-fracture-etch (FFE) studies have demonstrated gap junctions between fiber cells. Several workers have observed expanses of square crystallinity in fiber cell membranes with a lattice constant of 6-7 nm. This has usually been attributed variously to artifact induced by calcium, pH or proteolytic enzymatic digestion. Square arrays have been seen in isolated fractions of fiber cell membranes prepared with detergents as minor components and dismissed as relatively insignificant and either related or unrelated to gap junctions. Some have regarded them as a form of gap junction.

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