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G Zampighi

Publications and source records attributed to G Zampighi.

35 records · Page 2Linked to original sources
PubMed1980

On the electrotonic coupling mechanism of crayfish segmented axons: temperature dependence of junctional conductance.

It is generally accepted that the mechanism for electrotonic coupling involves the presence of hydrophilic channels connecting the cytoplasm of neighboring cells. These channels are presumed to be water filled holes. To test this hypothesis, we measured the temperature dependence of coupling parameters and calculated the specific resistance of junctional synapses of crayfish segmented axons. Results demonstrate that: (i) low temperature increases the junctional resistance in a manner that depends on the time course of cooling; (ii) the specific junctional resistance is, at most, 1-20 omega cm2. These results are consistent with a hypothesis of cell communication based on hydrophilic channels and suggest the presence of a temperature-dependent component of these channels.

Action Potentials↗
PubMed1980

Structure of the junction between communicating cells.

An 18-A resolution map of the 'gap junction' has been obtained by electron microscopy. The protein oligomer in the junctional membranes, the 'connexon', is a cyclinder composed of six subunits which are titled around its axis. Analysis of two different subunit configurations suggests how the connexon might regulate the passage of small molecules between cell interiors.

Animals↗
PubMed1980

On the structure of isolated junctions between communicating cells.

Gap junctions are specialized regions of contract between apposed plasma membranes of communicating cells. They are composed of hexagonally arranged units (connexons) embedded in plasma membranes and linked together in the extracellular space. The three-dimensional structure of the connexon was obtained by Fourier analysis on specimens of isolated rat liver gap junctions. The connexon is an annular oligomer, composed of six subunits, that protrudes from both sides of the plasma membrane. The subunits are tangentially displaced about the connexon axis. A narrow channel is located along the connexon axis spanning the thickness of the junction, but it is greatly reduced in the hydrophobic zones of the membranes. Two closely related forms of isolated gap junctions which have different connexon subunit structures but the same hexagonal lattice, were obtained. The transition between the two forms of communicating junctions seen in isolation is produced by radial inward motion of the connexon subunits near their cytoplasmic surfaces and a reduction of their inclination tangential to the 6-fold axis. Similar rearrangement of essentially rigid subunits embedded in the membrane could provide a mechanism for modulation of the junction permeability.

Animals↗
PubMed1980

On gap junction structure.

We have studied the stain distribution within rat liver gap junctions for specimens prepared by thin sectioning and negative staining. Pools of stain molecules exist in two specific locations with respect to the distinctive morphological units (connexons) of the junction. One pool of stain surrounds the connexons and is restricted to the extracellular space in the gap between the adjacent plasma membranes. The other pool of stain is located along in the central axis of each connexon, measures 1-2 nm in diameter and 4-5 nm in length, and is restricted to the gap region. On rare occasions, barely discernible linear densities seem to extend from this latter pool of stain and traverse the entire width of the junction. The data indicate the existence of a hydrophilic cavity along the central axis of te connexon which, in most instances, is restricted to the gap region. However, the precise depth to which this cavity may further extend along the connexon axis is still uncertain.

Animals↗
PubMed1980

Characterization of apolipoprotein B from human serum low density lipoprotein in n-dodecyl octaethyleneglycol monoether: an electron microscope study.

We have studied the structure of the totally delipidated polypeptide (apolipoprotein B [apo B]) present in low-density serum lipoprotein in detergent (n-dodecyl octaethyleneglycol monoether) solution by electron microscopy. The protein-detergent complex appears as a rod-shaped particle, 75-80 nm long and 4.5-5.5 nm wide. The volume of this particle is consistent with the previously published composition reported by Watt and Reynolds (1980, Biochemistry 19:1593-1598) of two copies of apo B and five to six equivalent micelles of detergent. The asymmetric particle possesses a high degree of flexibility and a strong tendency to self-associate in an orderly fashion. The extent of this association is pH dependent.

Apolipoproteins↗
PubMed1978

Fine structure of the electrotonic synapse of the lateral giant axons in a crayfish (Procambarus clarkii).

The electrotonic synapse of lateral giant axons of the crayfish was studied by conventional thin sectioning. The most prominent membrane specialization observed in this synaptic region is the communicating junction. It is characterized by a close apposition of the two axonal membranes which are separated by a 4--5 nm wide gap. Other characteristics of the junction are an array of particles spaced about 20--22 nm apart and a row of vesicles symmetrically arranged at the cytoplasmic leaflets of each membrane. The communicating junction does not cover the entire surface of the electrotonic synapse. Indeed, we have found other specializations such as: finger-like Schwann cell processes extending between synaptic membranes, saccular invaginations of one synaptic membrane into its axon, and coated vesicles continuous with one of the membranes. In addition, large vesicular pieces of the communicating junctions, with their accompanying vesicles, appeared to extend deeply inside the axoplasm. The morphological appearance of the communicating junction is found to be different from the one reported for mammalian maculae communicans such as liver or heart muscle. This is surprising because, regardless of their morphological differences, both junctions seem to transmit electrotonically.

Animals↗
PubMed1976

Regular structures in unit membranes. III. Further observations on the particulate component of the suckling rat ileum endocytic membrane complex.

Further morphological observations on the particulate components decorating the lumenal surfaces of membranes of the endocytic complex of the epithelial cells of the suckling rat ileum are presented. The particles each measure approximately 7.5 nm across and give the appearance of the capital letter H in frontal view. They consist of the enzyme n-acetyl-beta-glucosaminidase (NAG). They are arranged in rows called "decorated strips" with the symmetrical lateral bars in register and spaced approximately 14.5 nm apart. Decorated strips lie side-by-side in the external (lumenal) surface of the membrane. They are parallel and sometimes spaced approximately 14.5 nm apart making an orthogonal lattice. The lateral spacing between the decorated strips under certain conditions is reduced and sometimes there is shear between the adjacent ones. Occasionally, shear is present within the decorated strips themselves, with slight displacement of the two sides of each H-shaped particle. A purified preparation of these membranes has been studied by electron microscopy using thin sectioning, negative stain, Markham translation and optical diffraction computer image reconstruction methods. The individual particles comprising the array can be seen in the membrane surface in profile view when dried in a pool of negative stain. They appear either triangular or diamond-shaped in such views. If triangular, they appear to consist of three domains at the corners of an equilateral triangle. One side of each triangular figure is parallel to the membrane surface but separated from it by a dense band of negative stain approximately 2 nm thick that runs along the surface of the membrane. Sometimes a fourth symmetrical domain is visible within this dense band, giving a diamond-shaped figure. This fourth domain connects the particle to the membrane. Thus, each H-shaped particle is a double structure, with each half in profile view appearing as a diamond figure of four symmetrical domains. Each H-shaped particle is believed to consist of either two or four molecules of NAG.

Animals↗
PubMed1976

Regular structures in unit membranes. II. Morphological and biochemical characterization of two water-soluble membrane proteins isolated from the suckling rat ileum.

Specialized plasma membranes from the endocytic complex of ileal epithelial cells of suckling rats were isolated by differential flotation. Thin-section and negative-stain electron microscopy showed the luminal surfaces of these membranes to be covered by an ordered array of particles 14.5-nm separations in long rows. This particulate coating was released from the membrane surfaces by 10 mM CaCl2 and recovered free of membranes after dialysis against 0.5 mM EGTA and high-speed centrifugation. Two proteins were resolved by gel filtration to be in supernate: n-acetyl-beta-glucosaminidase and a filamentous protein which attaches n-acetylglucosaminidase to the membrane surface thereby providing bidirectionality to the array of enzyme. We believe that the filamentous protein has not been previously described. Therefore we have called it ligatin from the latin ligare, which translates "to bind together". Furthermore, we suggest that the membranes of the endocytic complex contain sites for the extracellular digestion of carbohydrate moieties in the maternal milk.

Animals↗
PubMed1975

On the connection between the transverse tubules and the plasma membrane in frog semitendinosus skeletal muscle. Are caveolae the mouths of the transverse tubule system?

The transverse tubular system (TTS) of skeletal muscle fibers represents the morphological basis for the inward spread of conduction of the electrical signal that triggers muscle contraction. A historical account of the main steps contributing to the elucidation of the structure and function of the TSS has been presented by Huxley (1971). While the localization of the TSS and its association with the sarcoplasmic reticulum (SR) is well documented; there is still a need further to develop our knowledge of the morphology of the connection between the TSS and the plasma membrane. It is generally believed that the TSS opens directly to the extracellular space and that there is continuity between its membrane and the sarcolemma. However, direct observation of such a connection has been clearly shown only for the myotome of fish (Franzini-Armstrong and Porter, 1964). In other muscle fibers, only indirect evidence of the connection has been provided by experiments showing penetration of extracellular tracers into the TSS. These extracellular markers were also observed inside another membrane-bounded compartment consisting of round profiles named "caveolae" (Yamada, 1955) or "pinocytotic vesicles" (Ashurst, 1969). The present study deals with the communication between the TTS, caveolae, and plasma membrane (Peachey, 1965); Ezerman and Ishikawa, 1967; Schiaffino and Margreth, 1968; and Rayns et al., 1968). A detailed study of the caveolae compartment was undertaken with ruthenium red as an electron-dense tracer. As a result of this study, we propose that in certain species the caveolae compartment represents the transitional region in the connection between the TSS and the sarcolemma.

Animals↗
PubMed1973

Fine structure of the synaptic discs separated from the goldfish medulla oblongata.

Synaptic discs are structures localized in the club ending synapses on the Mauthner cell lateral dendrite of the goldfish medulla oblongata. The synaptic discs present a hexagonal array of particles approximately 8.5 nm center-to-center when observed in en face view. This lattice covers the entire surface Divalent cations are important in the stabilization of this particular hexagonal array of particles When a synaptic disc-rich fraction is treated with chelating agents (EDTA or EGTA), definite changes occur in the hexagonal lattice. First, the synaptic membranes show zones without particles interspersed with zones covered with the hexagonal array of particles Second, the synaptic discs break down and a new structure characterized by two parallel dense bands (7 nm each), separated by a 4 nm gap, is observed. The negative stain fills the gap region showing striations spaced approximately 10 nm center-to-center crossing the gap, but it does not penetrate the dense bands This "double band" structure is interpreted as an edge on view of a fragment of the synaptic membrane complex. Further treatment of this fraction with a chelating agent plus 0.3% deoxycholate produces an increase in the number of double band structures. However, EDTA plus Triton X-100 (a treatment known to produce solubilization of membrane proteins) never shows such double band structure An ordered material was observed associated with the cytoplasmic leaflets of the double bands This material consists of rows of beads approximately 4 nm in diameter and spaced at intervals of approximately 7 nm. Each of these beads is joined to the band by a thin stalk.

Animals↗