Loose-myelin of giant axons in the earthworm; freeze-fracture characteristics of the glial membranes after thermal acclimation and rapid change of temperature

1981 ◽  
Vol 5 ◽  
pp. 32 ◽  
Author(s):  
N LANE ◽  
B ROOTS
Keyword(s):  
Rapid Change ◽  
Freeze Fracture ◽  
Thermal Acclimation ◽  
Fracture Characteristics ◽  
Giant Axons

scholarly journals Low resistance junctions in crayfish. Structural changes with functional uncoupling.

1976 ◽  
Vol 70 (2) ◽  
pp. 419-439 ◽  
Author(s):  
C Peracchia ◽  
A F Dulhunty
Keyword(s):  
Gap Junctions ◽  
Conformational Changes ◽  
Structural Changes ◽  
Freeze Fracture ◽  
Particle Diameter ◽  
Electrical Measurements ◽  
Thin Sections ◽  
Giant Axons ◽  
Intramembrane Particles ◽  
Center Distance

Electrical uncoupling of crayfish septate lateral giant axons is paralleled by structural changes in the gap junctions. The changes are characterized by a tighter aggregation of the intramembrane particles and a decrease in the overall width of the junction and the thickness of the gap. Preliminary measurements indicate also a decrease in particle diameter. The uncoupling is produced by in vitro treatment of crayfish abdominal cords either with a Ca++, Mg++-free solution containing EDTA, followed by return to normal saline (Van Harreveld's solution), or with VAn Harreveld's solution containing dinitrophenol (DNP). The uncoupling is monitored by the intracellular recording of the electrical resistance at a septum between lateral giant axons. The junctions of the same septum are examined in thin sections; those of other ganglia of the same chain used for the electrical measurements are studied by freeze-fracture. In controls, most junctions contain a more or less regular array of particles repeating at a center to center distance of approximately 200 A. The overall width of the junctions is approximately 200 A and the gap thickness is 40-50 A. Vesicles (400-700 A in diameter) are closely apposed to the junctional membranes. In uncoupled axons, most junctions contain a hexagonal array of particles repeating at a center to center distance of 150-155 A. The overall width of the junctions is approximately 180 A and the gap thickness is 20-30 A. These junctions are usually curved and are rarely associated with vesicles. Isolated, PTA-stained junctions, also believed to be uncoupled, display similar structural features. There are reasons to believe that the changes in structure and permeability are triggered by an increase in the intracellular free Ca++ concentration. Most likely, the changes in permeability are caused by conformational changes in some components of the intramembrane particles at the gap junctions.

scholarly journals The periaxonal space of crayfish giant axons.

1983 ◽  
Vol 82 (2) ◽  
pp. 221-244 ◽  
Author(s):  
P Shrager ◽  
J C Starkus ◽  
M V Lo ◽  
C Peracchia
Keyword(s):  
Glial Cell ◽  
Current Flow ◽  
Freeze Fracture ◽  
Extracellular Fluid ◽  
Outward Current ◽  
Thin Layers ◽  
Rapid Phase ◽  
Thin Sections ◽  
Giant Axons ◽  
Periaxonal Space

The influence of the glial cell layer on effective external ion concentrations has been studied in crayfish giant axons. Excess K ions accumulate in the periaxonal space during outward K+ current flow, but at a rate far below that expected from the total ionic flux and the measured thickness of the space. At the conclusion of outward current flow, the external K+ concentration returns to normal in an exponential fashion, with a time constant of approximately 2 ms. This process is about 25 times faster than is the case in squid axons. K+ repolarization (tail) currents are generally biphasic at potentials below about -40 mV and pass through a maximum before approaching a final asymptotic level. The initial rapid phase may in part reflect depletion of excess K+. After block of inactivation and reversal of the Na+ concentration gradient, we could demonstrate accumulation and washout of excess Na ions in the periaxonal space. Characteristics of these processes appeared similar to those of K+. Crayfish glial cell ultrastructure has been examined both in thin sections and after freeze fracture. Layers of connective tissue and extracellular fluid alternate with thin layers of glial cytoplasm. A membranous tubular lattice, spanning the innermost glial layers, may provide a pathway allowing rapid diffusion of excess ions from the axon surface.

A reliable method for obtaining matched replicas of freeze-fractured cell suspensions

1980 ◽  
Vol 42 (1) ◽  
pp. 389-400
Author(s):  
M.H. Wilkinson ◽  
D.H. Northcote
Keyword(s):  
Reliable Method ◽  
Freeze Fracture ◽  
Cell Suspensions ◽  
Animal Cells ◽  
Fracture Characteristics ◽  
Sample Digestion ◽  
Isolated Protoplasts ◽  
Glass Capillaries ◽  
Excellent Preservation ◽  
Membrane Ultrastructure

A method that overcomes the majority of practical problems involved in performing matched freeze-fracture replication of cell suspensions is described. Specimens are rapidly frozen between copper support plates. The prior attachment of gold grids to the plates using Formvar ensures the exact alignment of corresponding grid squares and the production of a central fissure running through the specimen upon fracturing. Grids, with replicas permanently attached, are removed from the support plates by dissolving the Formvar. Sample digestion and rinsing of replicas is by a gentle procedure employing glass capillaries as a means of handling the grids. Matched replication of plant and animal cells has been achieved by this methods. Apart from the excellent preservation of the membrane ultrastructure of unfixed cells and the capacity for matching both membrane halves this technique also enhances the fracture characteristics of certain specimens, notably isolated protoplasts, providing larger fracture faces than are obtained by the knife-splintering method.

Freeze-fracture characteristics of insect gustatory and olfactory sensilla. II. Cuticular features

1984 ◽  
Vol 179 (3) ◽  
pp. 305-321 ◽  
Author(s):  
Fran M. van der Wolk ◽  
B. Ph. M. Menco ◽  
H. Van Der Starre
Keyword(s):  
Freeze Fracture ◽  
Olfactory Sensilla ◽  
Fracture Characteristics

scholarly journals Quenched flow analysis of exocytosis in Paramecium cells: time course, changes in membrane structure, and calcium requirements revealed after rapid mixing and rapid freezing of intact cells.

1991 ◽  
Vol 113 (6) ◽  
pp. 1295-1304 ◽  
Author(s):  
G Knoll ◽  
C Braun ◽  
H Plattner
Keyword(s):  
Membrane Fusion ◽  
Time Course ◽  
Rapid Change ◽  
Freeze Fracture ◽  
Microscopic Analysis ◽  
Rapid Freezing ◽  
Electron Microscopic ◽  
Intact Cells ◽  
Rapid Mixing ◽  
Time Required

Synchronous exocytosis in Paramecium cells was analyzed on a subsecond time scale. For this purpose we developed a quenched flow device for rapid mixing and rapid freezing of cells without impairment (time resolution in the millisecond range, dead time approximately 30 ms). Cells frozen at defined times after stimulation with the noncytotoxic secretagogue aminoethyldextran were processed by freeze substitution for electron microscopic analysis. With ultrathin sections the time required for complete extrusion of secretory contents was determined to be less than 80 ms. Using freeze-fracture replicas the time required for resealing of the fused membranes was found to be less than 350 ms. During membrane fusion (visible 30 ms after stimulation) specific intramembranous particles in the cell membrane at the attachment sites of secretory organelles ("fusion rosette") disappear, possibly by dissociation of formerly oligomeric proteins. This hitherto unknown type of rapid change in membrane architecture may reflect molecular changes in protein-protein or protein-lipid interactions, presumably crucial for membrane fusion. By a modification of the quenched flow procedure extracellular [Ca++] during stimulation was adjusted to less than or equal to 3 x 10(-8) M, i.e., below intracellular [Ca++]. Only extrusion of the secretory contents, but not membrane fusion, was inhibited. Thus it was possible to separate both secretory events (membrane fusion from contents extrusion) and to discriminate their Ca++ requirements. We conclude that no Ca++ influx is necessary for induction of membrane fusion.

Ultrastructural Investigations of the Contractile Filaments of Amoebae

1974 ◽  
Vol 32 ◽  
pp. 188-189
Author(s):  
P.L. Moore
Keyword(s):  
Cytoplasmic Streaming ◽  
Three Dimensional ◽  
Freeze Fracture ◽  
Amoeboid Movement ◽  
Different Types ◽  
Chemical Conditions ◽  
Complete Interpretation

Previous freeze fracture results on the intact giant, amoeba Chaos carolinensis indicated the presence of a fibrillar arrangement of filaments within the cytoplasm. A complete interpretation of the three dimensional ultrastructure of these structures, and their possible role in amoeboid movement was not possible, since comparable results could not be obtained with conventional fixation of intact amoebae. Progress in interpreting the freeze fracture images of amoebae required a more thorough understanding of the different types of filaments present in amoebae, and of the ways in which they could be organized while remaining functional.The recent development of a calcium sensitive, demembranated, amoeboid model of Chaos carolinensis has made it possible to achieve a better understanding of such functional arrangements of amoeboid filaments. In these models the motility of demembranated cytoplasm can be controlled in vitro, and the chemical conditions necessary for contractility, and cytoplasmic streaming can be investigated. It is clear from these studies that “fibrils” exist in amoeboid models, and that they are capable of contracting along their length under conditions similar to those which cause contraction in vertebrate muscles.

Photoreceptor disk membrane substructures by means of the complementary freeze-fracture-replica methods

1978 ◽  
Vol 36 (2) ◽  
pp. 156-157
Author(s):  
A. Tonosaki ◽  
M. Yamasaki ◽  
H. Washioka ◽  
J. Mizoguchi
Keyword(s):  
Cell Membranes ◽  
Freeze Fracture ◽  
Purple Membrane ◽  
Remarkable Case ◽  
Single Face ◽  
Disk Membrane ◽  
Associated Proteins ◽  
Photoreceptor Membranes

A vertebrate disk membrane is composed of 40 % lipids and 60 % proteins. Its fracture faces have been classed into the plasmic (PF) and exoplasmic faces (EF), complementary with each other, like those of most other types of cell membranes. The hypothesis assuming the PF particles as representing membrane-associated proteins has been challenged by serious questions if they in fact emerge from the crystalline formation or decoration effects during freezing and shadowing processes. This problem seems to be yet unanswered, despite the remarkable case of the purple membrane of Halobacterium, partly because most observations have been made on the replicas from a single face of specimen, and partly because, in the case of photoreceptor membranes, the conformation of a rhodopsin and its relatives remains yet uncertain. The former defect seems to be partially fulfilled with complementary replica methods.

Decoration of specific sites on freeze-fractured membranes

1978 ◽  
Vol 36 (2) ◽  
pp. 140-141
Author(s):  
H. Gross ◽  
H. Moor
Keyword(s):  
Pure Water ◽  
Freeze Fracture ◽  
Chemical Properties ◽  
Surface Forces ◽  
Sulfate Pentahydrate ◽  
Copper Sulfate Pentahydrate ◽  
Physico Chemical ◽  
Water Of Hydration ◽  
Small Container ◽  
Binding Forces

Fracturing under ultrahigh vacuum (UHV, p ≤ 10-9 Torr) produces membrane fracture faces devoid of contamination. Such clean surfaces are a prerequisite foe studies of interactions between condensing molecules is possible and surface forces are unequally distributed, the condensate will accumulate at places with high binding forces; crystallites will arise which may be useful a probes for surface sites with specific physico-chemical properties. Specific “decoration” with crystallites can be achieved nby exposing membrane fracture faces to water vopour. A device was developed which enables the production of pure water vapour and the controlled variation of its partial pressure in an UHV freeze-fracture apparatus (Fig.1a). Under vaccum (≤ 10-3 Torr), small container filled with copper-sulfate-pentahydrate is heated with a heating coil, with the temperature controlled by means of a thermocouple. The water of hydration thereby released enters a storage vessel.

Sign in / Sign up

Export Citation Format

Share Document