Metabolic stabilization of acetylcholine receptors in vertebrate neuromuscular junction by muscle activity

The effects of muscle activity on the growth of synaptic acetylcholine receptor (AChR) accumulations and on the metabolic AChR stability were investigated in rat skeletal muscle. Ectopic end plates induced surgically in adult soleus muscle were denervated early during development when junctional AChR number and stability were still low and, subsequently, muscles were either left inactive or they were kept active by chronic exogenous stimulation. AChR numbers per ectopic AChR cluster and AChR stabilities were estimated from the radioactivity and its decay with time, respectively, of end plate sites whose AChRs had been labeled with 125I-alpha-bungarotoxin (alpha-butx). The results show that the metabolic stability of the AChRs in ectopic clusters is reversibly increased by muscle activity even when innervation is eliminated very early in development. 1 d of stimulation is sufficient to stabilize the AChRs in ectopic AChR clusters. Muscle stimulation also produced an increase in the number of AChRs at early denervated end plates. Activity-induced cluster growth occurs mainly by an increase in area rather than in AChR density, and for at least 10 d after denervation is comparable to that in normally developing ectopic end plates. The possible involvement of AChR stabilization in end plate growth is discussed.     

黄绿绿僵菌对褐飞虱侵染过程的扫描电镜观察

本实验利用扫描电镜观察了黄绿绿僵菌Metarhizium flavoviride菌株分生孢子对褐飞虱Nilaparvata lugens(St(a)l)的侵染过程.结果表明:分生孢子多分布在褐飞虱节间膜、体表的褶皱凹陷等部位,主要以芽管或产生附着胞入侵,然后在体表长出菌丝和产孢.菌体进入寄主血腔后,利用体腔内营养大量增...     

Development of a procedure for autoradiographic localization of carbonic anhydrase at the electron microscope level

A method for preparing tissue suitable for electron microscope autoradiographic localization of carbonic anhydrase is described. Radioactivity is in the form of 3H-acetazolamide, a specific inhibitor of carbonic anhydrase. Tissues fixed in glutaraldehyde, dehydrated in ethylene glycol followed by cellosolve as a transition fluid, and embedded in epoxy resin, were found to retain most (74%) of the label. Electron micrographs of avian gastric mucosa prepared in this manner are shown. Other methods of preparation were explored and resulted in considerable losses of label or in inadequately preserved tissue. Light microscope autoradiographic localization of gastric mucosa, shell gland, chorioallantoic membrane, and skeletal muscle compare well with previous localizations.     

Observations on estuarine microfouling using the scanning electron microscope

Scanning electron microscopy was used to observe microbiological primary fouling of glass surfaces exposed in estuarine waters. Observations on clean glass, and glass treated with water-repellent coatings, showed that bacterial slimes adhered less strongly to the waterrepellent glass. An experiment using pure cultures of bacteria and latex particles showed that attached bacteria promoted the settlement of latex particles on the glass.     

Quantitation of junctional and extrajunctional acetylcholine receptors by electron microscope autoradiography after (125)I-α-bungarotoxin binding at mouse neuromuscular junctions

The distribution and quantitation of 125I-alpha-bungarotoxin (alpha-BTX) binding sites and thus acetylcholine receptor (AChR) were determined in mouse sternomastoid muscle by electron microscope autoradiography. We found that a valid criterion for receptor saturation at the neuromuscular junction was the complete elimination of neurally evoked tetanic muscle contractions, since, when such a criterion was used for the endpoint of toxin incubation, alpha-BTX was bound to approximately 90% of total available endplate sites. When, without implying localization, the presynaptic axonal membrane was used as a convenient reference structure, the concentration of alpha-BTX relative to this membrane was determined to be 46,000 +/- 27% sites/mum2.     

Subunit structure and peptide mapping of junctional and extrajunctional acetylcholine receptors from rat muscle.

We have purified the junctional acetylcholine receptor from normal rat skeletal muscle and compared its structure with that of the extrajunctional receptor from denervated muscle. The two receptors from leg muscle were distinguished by isoelectric focusing and by reaction with sera from patients with myasthenia gravis. The junctional form of the acetylcholine receptor was purified from normal leg muscle by affinity chromatography on concanavalin A/Sepharose and cobrotoxin/Sepharose followed by sucrose gradient centrifugation. Analysis of radioiodinated receptor by polyacrylamide gel electrophoresis in sodium dodecyl sulfate indicated that the subunit structure of the junctional receptor was similar to that previously determined for the extra-junctional form (Froehner, S. C., et al. (1977) J. Biol. Chem. 252, 8589-8596), with major polypeptides, whose apparent molecular weights in 9% polyacrylamide gels were 45 000 and 51 000. In addition, several minor polypeptides were found. When the two receptors were labeled with different isotopes of iodine and run together on a sodium dodecyl sulfate gel, the subunits of one receptor could not be resolved from those of the other. As seen earlier with the extrajunctional form, the affinity alkylating reagent [3H]MBTA labeled the 45 000- and 49 000-dalton polypeptides of the junctional receptor. Peptide mapping showed that the two MBTA binding subunits are structurally related, although they are unrelated to the other polypeptides, and that the 45 000- and 51 000-dalton polypeptides of the junctional receptor were indistinguishable from those of the extrajunctional receptor. In addition, peptide mapping of the four subunits of acetylcholine receptor isolated from Torpedo californica electric organ showed that these four polypeptides appear to be structurally unrelated.     

Studies on perithecium of Ceratocystis stenoceras by a scanning electron microscope

The surface and cavity of the perithecium of Ceratocystis stenoceras were studied with a scanning electron microscope.The body was spherical, 96–231 in diameter, and the surface was covered with hyphae. The neck was a lanky hollow cylinder and the wall consisted of a bundle of tubular hyphae encircling a central canal. A whorl of hyaline hyphae was found at the tip of the neck. The surface of the neck from the body to a distance of about 1/6 was rough and warty. But the surface of the neck above that place was smooth, on which a regular design could be seen. The wall of the neck near the body consisted of 5–6 layers of cells. However, the wall at the tip was of 1–2 layers of cells. The cavity was filled with ascospores. They were like segments of an orange of 1 × 2 with smooth surface.     

Distribution and turnover rate of acetylcholine receptors throughout the junction folds at a vertebrate neuromuscular junction

The distribution and turnover rate of acetylcholine receptors labeled with 125I-alpha-bungarotoxin were examined in innervated mouse sternomastoid muscle by electron microscope autoradiography using the "mask" analysis procedure. We compared the total population of receptors with receptors newly inserted at the junction 2 d after inactivation with nonradioactive alpha-bungarotoxin, both at the top (thickened) region of the postjunctional folds (pjm) and the nonthickened bottom folds. We found that the receptor site density was approximately 10 times greater on the thickened pjm than on the nonthickened bottom folds for both total and newly inserted receptors. This ratio does not change significantly during a 6-d period after labeling the new receptors. Furthermore, calculated values for turnover time of receptors show that both total and newly inserted receptors at both regions of the junctional folds have half-lives for degradation within the range given in the literature for slow junctional receptors. These data exclude a simple migration model whereby receptors are preferentially inserted in the nonthickened region of the junctional folds and then migrate into the thickened membrane at a rate equal to the turnover rate of the receptors.     

A scanning electron microscope study of concanavalin a receptors on retinal rod cells labeled with latex microspheres

Con A-methacrylate microsphere conjugates prepared by a two-step glutaraldehyde reaction were used to label Con A-binding sites on bovine rod photoreceptor cells for visualization by scanning electron microscopy. A dense distribution of markers was observed on the surface of the rod outer segment, the inner segment, and the synaptic region. Disk membranes also appear to be heavily labeled with the Con A-microsphere conjugates. The Con A inhibitor, α-methyl mannoside, inhibited the binding of the conjugate to the surface of these visual cells.     

Examination of several selected fungi by scanning electron microscope

Scanning electron microscopy with high resolution and great depth of focus has been known to be able to show the fine features of surface ornamentation of fungi, and with this technique we could obtain the interesting results about the surface structures of the selected fungi,Penicillium chrysogenum, Aspergillus niger, Aspergillus oryzae andCandida utilis.     

Wear striation direction on primate teeth: a scanning electron microscope examination.

Two experimental methods were used to produce wear striations in one direction on unworn teeth. These include: (1) sliding 22 American Indian (Juntunen site, Michigan; Late Woodland) newly erupted incisors, by hand, across a flat grass surface covered with fine loose sand; and (2) using a unidirectional motor driven mechanical wear machine to draw 56 modern human dental extractions across a flat glass surface covered with silicon carbide powder of different grit sizes. A scanning electron microscope examination of individual wear striation morphology indicates that these wear striations begin with broad pits and have extending grooves that become narrower; characteristics that indicate the motion of wear. Patterns of wear striations on the worn dentitions of American Indians (Juntunen site) and the paleocene primate Phenacolemur pagei show similar characteristics and correspond to the buccal phase of mastication when the mandible is drawn upward, forward and slightly medially into centric occlusion. The data provided by this study can be used to test competing hypotheses concerning the direction of mandibular movement during mastication and food preparation.     

Glycosylation process in gonadotrophs: a quantitative electron microscope autoradiographic study with labeled glucosamine

Incorporation of [3H]glucosamine into dispersed anterior pituitary cells was studied by electron microscope autoradiography. Gonadotrophs were examined to determine the intracellular route and kinetic patterns of glycosylation. Studies were performed with cells from; (a) normal adult male rats; (b) rats orchidectomized 3 wk earlier; and (c) orchidectomized rats treated with tunicamycin. Our results show that incorporation of [3H]glucosamine first occurs in the rough endoplasmic reticulum (RER), then proceeds in the Golgi elements (where peripheral carbohydrates are attached). Treatment with tunicamycin results in a decrease in labeling of these 2 organelles. Comparison of the kinetic patterns in normal and castrated male rats shows that the accumulation of labeled glycosylated proteins in granules reaches a plateau within 2 hr post-pulse in normal rats, and rises during a 6-hr chase in castrated rats. However, because of the necessity for a rather long 15 min pulse, we cannot exclude the possibility that incorporation of glucosamine during the pulse may occur concomitantly in the RER and the Golgi saccules, to be followed by rapid transfer to the secretory granules.     

Mechanical wear of the gastropod radula: a scanning electron microscope study

The wear sustained by the teeth of the highly mineralized radula of Patella vulgata and the unmineralized radula of Agriolomax reticulatus has been studied with the scanning electron microscope. The unworn teeth of P. vulgata have tall pointed cusps and wear is first seen as a chipping of the tips then as abrasion. There is a well defined abraded surface giving the worn teeth a chisel shape. In cleaved teeth fibres ˜ 800 Å in diameter are observed parallel to the axis of the tooth. Evidence is presented for chemical etching and for the existence of a surface coat on the tooth. A. reticulatus teeth show wear over their whole surface. With the aid of the grooves in the jaw caused by the teeth the role of the jaw in flattening the radula and protracting and retracting the odontophore is confirmed. From the arrangement of the abraded surfaces on the teeth of P. vulgata it was deduced that the teeth rows are abraded one at a time while on a convex surface at or near the bending plane.