Biomedical subjects

X Z Song

Publications and source records attributed to X Z Song.

7 recordsLinked to original sources

PubMed2000

Electrostatic interactions regulate desensitization of the nicotinic acetylcholine receptor.

To determine the importance of electrostatic interactions for agonist binding to the nicotinic acetylcholine receptor (AChR), we examined the affinity of the fluorescent agonist dansyl-C6-choline for the AChR. Increasing ionic strength decreased the binding affinity in a noncompetitive manner and increased the Hill coefficient of binding. Small cations did not compete directly for dansyl-C6-choline binding. The sensitivity to ionic strength was reduced in the presence of proadifen, a noncompetitive antagonist that desensitizes the receptor. Moreover, at low ionic strength, the dansyl-C6-choline affinities were similar in the absence or presence of proadifen, a result consistent with the receptor being desensitized at low ionic strength. Similar ionic strength effects were observed for the binding of the noncompetitive antagonist [(3)H]ethidium when examined in the presence and absence of agonist to desensitize the AChR. Therefore, ionic strength modulates binding affinity through at least two mechanisms: by influencing the conformation of the AChR and by electrostatic effects at the binding sites. The results show that charge-charge interactions regulate the desensitization of the receptor. Analysis of dansyl-C6-choline binding to the desensitized conformation using the Debye-Hückel equation was consistent with the presence of five to nine negative charges within 20 A of the acetylcholine binding sites.

Animals↗

PubMed2000

[Reconstruction of the shoulder joint function in the older obstetrical palsy].

OBJECTIVE: To study the reconstructional method and effect of shoulder joint function in the older obstetrical palsy with medial rotation contracture deformity. METHODS: From April 1996 to July 1999, 7 patients of older obstetrical palsy were adopted in this study. Among them, there were 5 males and 2 females, aged from 13 to 21 years old. No previous operation history and the main deformity was medial rotation contracture of shoulder. During operation, these patients were treated with "Z"-shape elongation of the tendon of subscapular muscle, transfer of the tendons of latissimus dorsi and teres major muscle to the tendons of supraspinous and infraspinous muscles. RESULTS: Followed up for 6 to 44 months(averaged 19 months), the Gilbert grading and Mallet scoring were 1.57, 7.57 preoperatively versus 3.45, 10.86 postoperatively, the abduction and external rotation of the shoulder joints recovered obviously. CONCLUSION: It is an effective operation for the older obstetrical palsy with medial rotation contracture of shoulder.

Adolescent↗

PubMed1998

Protein-induced changes in nonplanarity of the porphyrin in nickel cytochrome c probed by resonance Raman spectroscopy.

The influence of the protein on the nonplanarity of the macrocycle for nickel(II)-reconstituted cytochrome c (NiCyt-c) has been investigated with pH-dependent resonance Raman and UV-visible absorption spectroscopy and molecular mechanics calculations. The spectra reveal that NiCyt-c near neutral pH has axially coordinated Ni, but below pH 3 and above pH 12, four-coordinate species predominate. The shape of the structure-sensitive Raman line nu10 of NiCyt-c is asymmetric and broad and it changes with pH. This broad line can be decomposed well into at least two sublines, a low-frequency line that results from a nonplanar conformer and a high-frequency line that arises from a nearly planar conformer. Upon lowering the pH from 3.0 to 1.0, the amount of the nonplanar conformer decreases relative to that of the planar conformer. The decreased nonplanarity can be accounted for in terms of the disruption of a hydrogen-bonding network in the peptide backbone upon lowering the pH. Molecular mechanics (MM) calculations on iron(III) and nickel(II) microperoxidase 5 (MP-5) as well as some model heme derivatives have been carried out in order to locate the part of the protein that causes the heme distortion observed in the X-ray crystal structures of cytochromes c. The energy-optimized structures of MP-5 and the model compounds were analyzed using the normal-coordinate structural decomposition method to specify and quantify the out-of-plane macrocyclic distortions. MM calculations for MP-5 show that two hydrogen bonds formed between the amide groups in the peptide backbone are important in maintaining the ruffled deformation of the macrocycle. All evidence presented supports the hypothesis that the nonplanar distortion of the porphyrin of cytochromes c is largely maintained by a relatively small protein segment including the cysteines, the amino acids between the cysteines, and the adjacent histidine ligand. Hydrogen bonding within the backbone of this segment is important in maintaining the conformation of the peptide that induces the porphyrin distortion.

Binding Sites↗

PubMed1996

Cellular and subcellular distribution of alpha 2A-adrenergic receptors in the visual cortex of neonatal and adult rats.

Activation of alpha 2-adrenergic receptors (alpha 2AR) in the cerebral cortex has been shown to modulate visually guided delayed response tasks as well as anxiety and depression. We used an antiserum directed specifically against the A subtype of alpha 2AR (alpha 2AAR) to determine the cell types and subcellular sites for noradrenergic reception mediated by this receptor in the adult and the developing rat visual cortices. Light microscopic examination of adult tissue revealed numerous labeled perikarya in layers II-VI, many of which appeared distinctly pyramidal. A few perikarya in layer I also were immunoreactive. In all layers, alpha 2AAR immunoreactivity (alpha 2AAR-ir) was present within proximal dendrites and fine processes. In neonatal tissue, there was an intense, distinct band of immunoreactivity spanning the layer composed of tightly packed immature cell bodies, i.e., the cortical plate. The band dissipated as this tier differentiated postnatally into the supragranular layers. Electron microscopy showed that the supragranular layers, which contain the highest density of noradrenergic fibers, also contain the highest areal density of labeled postsynaptic junctions beyond 2 weeks of age. Throughout the ages, the majority of immunoreactivity occurred at sites which, in single ultrathin sections, appeared to be nonjunctional sites of axons, dendrites, and in glial processes. Our observations indicate that (1) both pyramidal and nonpyramidal neurons are receptive to norepinephrine via alpha 2AAR, (2) alpha 2AAR synthesis is robust prior to synaptogenesis, and (3) alpha 2AAR operates both pre- and postsynaptically.

Animals↗

PubMed1990

[The pineal ultrastructure of the Mongolian ground squirrel, Citellus dauricus].

The distal part of pineal gland of the Mongolian ground squirrel was ultrastructurally studied. The gland was composed of low electron-dense parenchymal cells, among which glial cells, pigment cells, blood vessels and neural elements were occasionally interspersed. The pinealocytes contained numerous mitochondria, lysosomes, microtubules, microfilaments, Golgi apparatus and free ribosomes, as well as less prominent profiles of rough- and smooth-surfaced endoplasmic reticula and some cilia, centrioles, synaptic ribbons and few subsurface cisterns. Some pinealocytes were vacuolated. The content of the vacuoles released into the extracellular space by exocytosis could be observed. The gap junctions between pinealocytes were also observed. Of particular interest was that many mitochondria "fused together" and formed gap junction-like structure in about five percent pinealocytes. The pigment cell has a amorphous nucleus which contains many aggregated chromatin, its cell membrane has a few microvilli projecting into a central lumen, these features may indicated that this kind of cell differs either from the pinealocyte or astrocyte. There are axo-axonic synapses or axo-dendritic synapses between neuron processes or between neuron processes and pinealocytes.

Animals↗

PubMed1990

[Morphological changes in pinealocytes during the hibernation bout in the Mongolian ground squirrel, Citellus dauricus].

Adult Mongolian ground squirrels (Citellus dauricus) were kept at 5 degrees C in winter and divided into four experimental groups according to the bout length. The first group was not hibernating until decapitation. The bout length of the second group was between 4-10 days, the third group 11-17 days and the fourth group longer than 20 days. All pineals were sampled at the end of January. Morphometric analytical procedures were used to study the ultrastructure of the distal part of the pineal gland. The statistical results demonstrated that 1) the euthermic animals have larger cross areas of pinealocyte, longer and narrower Golgi apparatus and more number of saccules of each Golgi apparatus (P less than 0.01). But they also have smaller volume density of vaculoes, less lipid droplets and associated vesicles around Golgi apparatus (P less than 0.01). 2) the hibernating animals with variety of bout length had no significant differences in the number of mitochondria, lipid droplets, lysosomes, the size of Golgi apparatus and the cross areas of nucleus and cytoplasm (P greater than 0.05). However, the number and the cross areas of vacuoles were significantly increased with the bout length (P less than 0.01). This might suggest that the bout length was not related to the metabolic activity of pinealocytes in Citellus dauricus and vacuoles might play some important roles in maintenance of individual bout of hibernation in this species.

Animals↗

PubMed1989

[Clinical and experimental research on a kidney-tonifying prescription in preventing and treating children's hearing-loss induced by aminoglycoside antibiotic ototoxicity].

This paper reports 30 cases of hearing-loss induced by aminoglycoside antibiotic ototoxicity treated mainly with Kidney-tonifying herbs such as Herba Epimedii, Rhizoma Drynariae, Rhizoma Polygonati, Radix Polygoni Multiflori, Magnetitum and Rhizoma Acori Graminei, etc. After three month's treatment, the authors found that 19 cases had improved their hearing more than 15 db, among which there are 8 cases who had improved 15 db and 11 cases 30 db. The patients' hearing of pre-treatment and post-treatment were determined by BAR V-wave hearing threshold. In order to further prove that Kidney-tonifying prescription can antagonize the aminoglycoside antibiotic ototoxicity, animal experiments had been made. The authors chose guinea pigs for experimental animals, which were randomly divided into three groups: Kanamycin group, kanamycin with Kidney-tonifying herbs group, and control group. The indexes of the experiments were the animals' helix reflection index, BAR and observation of animals' cochlear under electron microscope. As a result, the damage to hair cell of Cortis organ has marked for the animals of kanamycin group, while for kanamycin with herbs group, it was obviously slighter (P less than 0.01). There was significant difference between the groups. The result indicates that Kidney-tonifying herbs had the effect of protecting the animals' hair cells of cortis organ against aminoglycoside antibiotic ototoxicity and thus protected the animals' hearing.

Adolescent↗