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J E Heuser

Publications and source records attributed to J E Heuser.

83 records · Page 5Linked to original sources
PubMed1979

Organization of acetylcholine receptors in quick-frozen, deep-etched, and rotary-replicated Torpedo postsynaptic membrane.

The receptor-rich postsynaptic membrane of the elasmobranch electric organ was fixed by quick-freezing and then viewed by freeze-fracture, deep-etching and rotary-replication. Traditional freeze-fracture revealed a distinct, geometrical pattern of shallow 8.5-nm bumps on the E fracture-face, similar to the lattice which has been seen before in chemically fixed material, but seen less clearly than after quick-freezing. Fracture plus deep-etching brought into view on the true outside of this membrane a similar geometrical pattern of 8.5-nm projections rising out of the membrane surface. The individual projections looked like structures that have been seen in negatively stained or deep-etched membrane fragments and have been identified as individual acetylcholine receptor molecules. The surface protrusions were twice as abundant as the large intramembrane particles that characterize the fracture faces of this membrane, which have also been considered to be receptor molecules. Particle counts have always been too low to match the estimates of postsynaptic receptor density derived from physiological and biochemical studies; counts of surface projections, however, more closely matched these estimates. Rotary-replication of quick-frozen, etched postsynaptic membranes enhanced the visibility of these surface protuberances and illustrated that they often occur in dimers, tetramers, and ordered rows. The variations in these surface patterns suggested that in vivo, receptors in the postsynaptic membrane may tend to pack into "liquid crystals" which constantly appear, flow, and disappear in the fluid environment of the membrane. Additionally, deep-etching revealed a distinct web of cytoplasmic filaments beneath the postsynaptic membrane, and revealed the basal lamina above it; and delineated possible points of contact between these structures and the membrane proper.

Acetylcholine↗
PubMed1978

T-tubule swelling in hypertonic solutions: a freeze substitution study.

Striated muscles from Rana pipiens have been exposed for variable periods of time to Ringer solutions made hypertonic by addition of either sucrose or sodium chloride. The muscles have been rapid-frozen and then prepared for electron microscopy by either freeze-substitution, freeze-fracture or cryoultramicrotomy. The only compartment greatly affected by hypertonicity is the transverse tubular system, which is visibly swollen. None of the elements of the sarcoplasmic reticulum increase in size.

Animals↗
PubMed1977

Selective enzymatic hydrolysis of nerve terminal phospholipids by beta-bungarotoxin: biochemical and morphological studies.

beta-Bungarotoxin, a presynaptic protein neurotoxin isolated from the venom of the snake Bungarus multicinctus, modifies release of neurotransmitter at the neuromuscular junction. The toxin has a potent phospholipase activity toward both natural membranes and phospholipid liposomes. Studies of ionic requirements and selective chemical modification demonstrate that beta-bungarotoxin can only modify synaptic transmission under conditions in which the phospholipase is active. Morphological studies on frog cutaneous pectoris neuromuscular junctions incubated with beta-toxin and horseradish peroxidase-conjugated beta-toxin support the hypothesis that beta-toxin specifically interacts with presynaptic plasma membranes and selectively hydrolyzes nerve terminal phospholipids.

Animals↗
PubMed1973

Evidence for recycling of synaptic vesicle membrane during transmitter release at the frog neuromuscular junction.

When the nerves of isolated frog sartorius muscles were stimulated at 10 Hz, synaptic vesicles in the motor nerve terminals became transiently depleted. This depletion apparently resulted from a redistribution rather than disappearance of synaptic vesicle membrane, since the total amount of membrane comprising these nerve terminals remained constant during stimulation. At 1 min of stimulation, the 30% depletion in synaptic vesicle membrane was nearly balanced by an increase in plasma membrane, suggesting that vesicle membrane rapidly moved to the surface as it might if vesicles released their content of transmitter by exocytosis. After 15 min of stimulation, the 60% depletion of synaptic vesicle membrane was largely balanced by the appearance of numerous irregular membrane-walled cisternae inside the terminals, suggesting that vesicle membrane was retrieved from the surface as cisternae. When muscles were rested after 15 min of stimulation, cisternae disappeared and synaptic vesicles reappeared, suggesting that cisternae divided to form new synaptic vesicles so that the original vesicle membrane was now recycled into new synaptic vesicles. When muscles were soaked in horseradish peroxidase (HRP), this tracerfirst entered the cisternae which formed during stimulation and then entered a large proportion of the synaptic vesicles which reappeared during rest, strengthening the idea that synaptic vesicle membrane added to the surface was retrieved as cisternae which subsequently divided to form new vesicles. When muscles containing HRP in synaptic vesicles were washed to remove extracellular HRP and restimulated, HRP disappeared from vesicles without appearing in the new cisternae formed during the second stimulation, confirming that a one-way recycling of synaptic membrane, from the surface through cisternae to new vesicles, was occurring. Coated vesicles apparently represented the actual mechanism for retrieval of synaptic vesicle membrane from the plasma membrane, because during nerve stimulation they proliferated at regions of the nerve terminals covered by Schwann processes, took up peroxidase, and appeared in various stages of coalescence with cisternae. In contrast, synaptic vesicles did not appear to return directly from the surface to form cisternae, and cisternae themselves never appeared directly connected to the surface. Thus, during stimulation the intracellular compartments of this synapse change shape and take up extracellular protein in a manner which indicates that synaptic vesicle membrane added to the surface during exocytosis is retrieved by coated vesicles and recycled into new synaptic vesicles by way of intermediate cisternae.

Animals↗
PubMed1973

Autoradiographic localization of new RNA synthesis in hypertrophying skeletal muscle.

Work-induced growth of rat soleus muscle is accompanied by an early increase in new RNA synthesis. To determine the cell type(s) responsible for the increased RNA synthesis, we compared light autoradiographs of control and hypertrophying muscles from rats injected with tritiated uridine 12, 24, and 48 h after inducing hypertrophy. There was an increased number of silver grains over autoradiographs of hypertrophied muscle. This increase occurred over connective tissue cells; there was no increase in the number of silver grains over the muscle fibers. Quantitative studies demonstrated that between 70 and 80% of the radioactivity in the muscle that survived fixation and washing was in RNA. Pretreatment of the animals with actinomycin D reduced in parallel both the radioactivity in RNA and the number of silver grains over autoradiographs. Proliferation of the connective tissue in hypertrophying muscle was evident in light micrographs, and electron micrographs identified the proliferating cells as enlarged fibroblasts and macrophages; the connective tissue cells remained after hypertrophy was completed. Thus, proliferating connective tissue cells are the major site of the increase in new RNA synthesis during acute work-induced growth of skeletal muscle. It is suggested that in the analysis of physiological adaptations of muscle, the connective tissue cells deserve consideration as a site of significant molecular activity.

Animals↗
PubMed1967

Ultrastructure of the prawn nerve sheaths. Role of fixative and osmotic pressure in vesiculation of thin cytoplasmic laminae.

The sheaths from freshly teased nerve fibers of the prawn exhibit a positive radial birefringence, consistent with their EM appearance as highly organized laminated structures composed of numerous thin cytoplasmic sheets or laminae bordered by unit membranes and arranged concentrically around the axon. The closely apposed membranes in these sheaths are fragile and often break down into rows of vesicles during fixation. Desmosome-like attachment zones occur in many regions of the sheath. The membranes within these zones resist vesiculation and thereby provide a "control" region for relating the type of vesicles formed in the fragile portions of the sheaths to the specific fixation conditions. It is proposed that during fixation the production of artifactual vesicles is governed by an interplay of three factors: (a) direct chemical action of the fixative on the polar strata of adjacent unit membranes, (b) osmotic forces applied to membranes during fixation, and (c) the pre-existing natural relations between adjacent membranes. It is found that permanganate best preserves the continuity of the membranes but will still produce vesicles if the fixative exerts severe osmotic forces. These results support other reports (19) of the importance of comparing tissues fixed by complementary procedures so that systematic artifacts will not be described as characteristic of the natural state.

Animals↗
PubMed1966

The fine structural organization of nerve fibers, sheaths, and glial cells in the prawn, Palaemonetes vulgaris.

In view of reports that the nerve fibers of the sea prawn conduct impulses more rapidly than other invertebrate nerves and look like myelinated vertebrate nerves in the light microscope, prawn nerve fibers were studied with the electron microscope. Their sheaths are found to have a consistent and unique structure that is unlike vertebrate myelin in four respects: (1) The sheath is composed of 10 to 50 thin (200- to 1000-A) layers or laminae; each lamina is a cellular process that contains cytoplasm and wraps concentrically around the axon. The laminae do not connect to form a spiral; in fact, no cytoplasmic continuity has been demonstrated among them. (2) Nuclei of sheath cells occur only in the innermost lamina of the sheath; thus, they lie between the sheath and the axon rather than outside the sheath as in vertebrate myelinated fibers. (3) In regions in which the structural integrity of the sheath is most prominent, radially oriented stacks of desmosomes are formed between adjacent laminae. (4) An approximately 200-A extracellular gap occurs around the axon and between the innermost sheath laminae, but it is separated from surrounding extracellular spaces by gap closure between the outer sheath laminae, as the membranes of adjacent laminae adhere to form external compound membranes (ECM's). Sheaths are interrupted periodically to form nodes, analogous to vertebrate nodes of Ranvier, where a new type of glial cell called the "nodal cell" loosely enmeshes the axon and intermittently forms tight junctions (ECM's) with it. This nodal cell, in turn, forms tight junctions with other glial cells which ramify widely within the cord, suggesting the possibility of functional axon-glia interaction.

Animals↗
PubMedDate not supplied

Purification and characterization of astrocyte-secreted apolipoprotein E and J-containing lipoproteins from wild-type and human apoE transgenic mice.

The varepsilon4 allele of apolipoprotein E (apoE) is a genetic risk factor for Alzheimer's disease (AD). In order to gain a better understanding of the molecular mechanisms by which apoE and possibly other apolipoproteins produced in the central nervous system (CNS) influence AD pathogenesis, we have purified and characterized the two most abundant apolipoproteins produced in the CNS, apoE and apoJ. We purified apoE and apoJ from primary cultures of mouse astrocytes, which were derived from transgenic mice expressing human apoE isoforms in the absence of mouse apoE. Utilizing antibody affinity columns, we were able to purify both human apoE3 and apoE4, as well as mouse apoJ-containing lipoproteins. Astrocyte-secreted human apoE was present in high density-like lipoproteins of three predominant sizes ranging from 8 to 15 nm in diameter. Mouse apoJ was in particles between 10 and 17 nm in diameter with a peak size range of approximately 11 nm. ApoE and apoJ were in distinct lipoproteins. Utilization of quick-freeze, deep-etch electron microscopy revealed the apoE particles were discs while the apoJ particles were smaller and more irregular in appearance. The lipid composition of apoE particles was very different from those containing apoJ. ApoE-particles contained a similar mass of apoE and lipid, with cholesterol and phospholipid being about equal in mass per particle. ApoJ-particles were relatively lipid poor (three parts protein, one part lipid), with phospholipids being much more abundant than cholesterol. Detailed characterization of phospholipid composition by electrospray ionization mass spectrometry analysis revealed ethanolamine glycerophospholipids to be the most abundant phospholipid present in both apoE and apoJ particles. Analysis of cerebrospinal fluid from apoE3 and apoE4 transgenic mice revealed that human and mouse apoE were in particles the same size as those secreted by astrocytes. Further use of physiological preparations of CNS-derived lipoproteins may allow for a detailed understanding of the role of these molecules in the normal brain and in diseases such as AD.

Animals↗