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C L Ma

Publications and source records attributed to C L Ma.

At least 19 recordsLinked to original sources
PubMed2002

Presynaptic modulation of GABAergic inhibition by GABA(B) receptors in the rat's inferior colliculus.

Whole-cell patch clamp recordings were made from neurons in a brain slice preparation of the inferior colliculus in 11-15-day-old rat pups. Synaptic responses were elicited by applying a current pulse to the lateral lemniscus just below the central nucleus of the inferior colliculus. To examine GABAergic inhibition in the inferior colliculus all excitatory postsynaptic potentials and glycinergic inhibitory postsynaptic potentials were blocked by bath application of their respective antagonists and the contribution of GABA(B) receptors was determined for the remaining inhibitory postsynaptic potentials. For most cells the isolated inhibitory postsynaptic potential was completely blocked by the GABA(A) receptor antagonist, bicuculline, but was unaffected by the GABA(B) receptor antagonist, phaclofen. The GABA(B) receptor agonist, baclofen (10-20 microM), decreased the amplitude of the inhibitory postsynaptic potentials. This effect was completely blocked by phaclofen. Baclofen did not increase the cell membrane conductance or alter the rate of firing produced by depolarization of the cell membrane. In contrast, muscimol, a GABA(A) receptor agonist, greatly increased membrane conductance and lowered the firing rate produced by depolarization. Our results indicate that GABAergic inhibition in the auditory midbrain can be reduced by the activation of GABA(B) receptors and suggest that the effects are presynaptic.

Animals↗
PubMed2001

Expressed sequence tags from a NaCl-treated Suaeda salsa cDNA library.

Past efforts to improve plant tolerance to osmotic stress have had limited success owing to the genetic complexity of stress responses. The first step towards cataloging and categorizing genetically complex abotic stress responses is the rapid discovery of genes by the large-scale partial sequencing of randomly selected cDNA clones or expressed sequence tags (ESTs). Suaeda salsa, which can survive seawater-level salinity, is a favorite halophytic model for salt tolerant research. We constructed a NaCl-treated cDNA library of Suaeda salsa and sequenced 1048 randomly selected clones, out of which 1016 clones produced readable sequences (773 showed homology to previously identified genes, 227 matched unknown protein coding regions, 16 anomalous sequences or sequences of bacterial origin were excluded from further analysis). By sequence analysis we identified 492 unique clones: 315 showed homology to previously identified genes, 177 matched unknown protein coding regions (101 of which have been found before in other organisms and 76 are completely novel). All our EST data are available on the Internet. We believe that our dbEST and the associated DNA materials will be a useful source to scientists engaging in stress-tolerance study.

Blotting, Northern↗
PubMed2001

Genetic selection in Saccharomyces of mutant mammalian adenylyl cyclases with elevated basal activities.

We show that co-expression of rat Galphas together with type I, II, IV, or VI mammalian adenylyl cyclase (AC) can suppress the growth defect of cyr1 strains of Saccharomyces cerevisiae, which lack a functional endogenous AC. Complemention of cvr1 is not observed in the absence of Galphas, indicating that the mammalian ACs retain their normal regulatory behavior in yeast. Selection for Galphas-independent growth of (cyr1 strains expressing type IV AC yielded several ACIV mutants with enhanced basal activity, each of which had a single amino acid substitution in the conserved C1a or C2a region of the protein. Expression of two of the mutant ACs in HEK293 cells resulted in increased levels of cAMP and elevated adenylyl cyclase activity. Further selection for reverting mutations in one of these constitutively active AC mutants yielded three independent intragenic suppressor mutations. The distribution of the activating and suppressor mutations throughout both C1a and C2a is consistent with a model in which the enhanced basal activity results from an increase in the affinity between C1a and C2a. These results demonstrate the utility of Saccharomyces as a tool for the identification of informative mutant forms of mammalian ACs.

Adenylyl Cyclases↗
PubMed2000

[Cloning and sequence analysis of RESA gene fragment of Plasmodium falciparum isolate FCC1/HN].

OBJECTIVE: To determine the nucleotide sequence of the 3'-termal of the RESA gene Plasmodium falciparum isolate FCC1/HN, and find out the differences of the sequences of RESA gene among isolate FCC1/HN, FC27, NF7 and Palo Alto. METHODS: 3'-terminal fragment of RESA gene of P. falciparum isolate FCC1/HN was amplified by PCR method, then was cloned into pMD18-T vector. The recombinant was screened and identified by BamHI + XhoI and PCR technique. The nucleotide sequence of the 3'-terminal of the RESA gene was determined by the dideoxy chain termination method. DNASTAR and BLAST software were used to compare and analyze the RESA gene sequences among the different isolates. RESULTS: The 3'-termal fragment of the RESA gene with about 846 bp was specifically amplified by PCR, the recombinant pMD18-T-RESA was successfully constructed. Different degrees of diversity of the RESA gene sequences were found among P. falciparum isolates FCC1/HN, FC27, NF7 and Palo Alto. CONCLUSION: There were differences in the sequences of RESA gene among the P. falciparum isolate FCC1/HN and three other isolates (FC27, NF7 and Palto alto).

Amino Acid Sequence↗
PubMed1998

GDNF protects the cochlea against noise damage.

Glial-derived neurotrophic factor (GDNF) was tested for its ability to prevent hearing and sensory cell loss in guinea pigs exposed to acoustic trauma. Hearing was measured prior to any treatment. Animals were exposed to damaging levels of noise either before or after local application of GDNF to one ear. Four weeks later, hearing and sensory cell loss was greater in the control ear than in the ear receiving GDNF before acoustic trauma or 2 h after trauma, but not 4 or 6 h after trauma. The results indicate that GDNF treatment in vivo can prevent cochlear sensory cell damage and hearing loss if present during or shortly after acoustic trauma.

Animals↗
PubMed1997

Cutaneous infection by Scedosporium apiospermum and its successful treatment with itraconazole.

We report the case of a 42-year-old man with a 13-year history of bilateral faciocervical infiltrative erythema, which had been misdiagnosed as tuberculoderma and which had failed to respond to treatment with adrenal corticosteroids and antituberculotics. On admission to the department, Scedosporium apiospermum was identified on lesion biopsies and fungus cultures as the causative agent and a diagnosis of cutaneous infection by S. apiospermum was made. This is the first report of chronic skin granuloma caused by S. apiospermum in China. Treatment with oral itraconazole (100-400 mg/day) led to clinical cure within 4 months.

Adult↗
PubMed1991

The laryngeal mask airway--clinical experience.

The laryngeal mask airway (LMA), a new type of airway, when it is inserted blindly into the hypopharynx forms a seal around the larynx and allows easy and convenient spontaneous or controlled positive pressure ventilation. A clinical application of the LMA to 70 surgical patients in our hospital have been evaluated. LMA was successfully applied to 68 (97%) patients who all received general anesthesia with unobstructed controlled ventilation. The patency of the airway did not change throughout the course of anesthesia. There were 2 patients whose airway was obstructed at the first attempt due to downfolding of epiglottis; in one of them the obstruction was confirmed by flexible fibreoptic laryngoscopy. Subsequent placement was successful in these 2 patients. Insertion failure was seen in 2 patients respectively due to small mouth and excessive salivation. The placement of LMA does not require laryngoscopy and there is no fear of misplacement in the esophagus. It becomes obvious that the LMA would substantially gain a place in the armamentarium in anesthesia and we think that its use would be of interest to anesthesiologists.

Adult↗
PubMed1990

A fluorescent analogue of hydrin 1: a new probe for vasotocin receptors.

Hydrin 1 is the biosynthetic precursor of vasotocin in Xenopus laevis. We have synthesized deamino and fluorescein analogues of hydrin 1 and characterized their physiological action in the urinary bladder of the toad, Bufo marinus. 1-Deamino-hydrin 1 (d-hydrin) was more potent than vasotocin in stimulating osmotic water flow across intact bladders and more potent than vasotocin in displacing tritium-labeled vasopressin [( 3H]AVP) from cell membranes. 1-Deamino-[11-lysine (fluorescein)]-hydrin 1 (flu-hydrin) was found to be the most potent fluorescent vasotocin receptor probe synthesized to date. Flu-hydrin increased osmotic water flow across bladders with a half-maximal effective dose (ED50) value of 6 x 10(-10) M and displaced [3H]AVP from membranes with a half-maximal concentration (IC50) value of 3 x 10(-9) M. The hydrosmotic response to flu-hydrin was blocked by 1-deamino-[4-lysine (p-azido-benzoyl)]arginine vasotocin [d4Lys(N3)-AVT]. Epifluorescence light microscopic studies showed vesicular uptake of flu-hydrin at the basolateral membrane of toad bladder epithelial cells, and this uptake was blocked by d4Lys(N3)AVT. This study shows that d-hydrin can serve as a foundation molecule to which reporter groups, such as fluorescent residues, can be attached with better preservation of hydrosmotic activity than is possible with similar modifications of vasotocin.

Amino Acid Sequence↗
PubMed1990

[cis-diamminedichloroplatinum cochlear toxicity].

Twenty-nine guinea pigs were divided into three groups. The first group received distilled water 2 ml/kg ip daily; the second group received DDP 2 mg/kg ip daily; and the third group DDP 4 mg/kg ip daily. ABR hearing threshold was tested before injection. Twenty-four hours after systemic administration, ABR hearing threshold was tested again. The animals were killed and the cochlear specimens were observed under light, scanning and transmission electron microscopes. No abnormality regarding ABR hearing threshold and cochlear morphology was observed in the first group. In the second group, ABR hearing threshold was elevated, inner and outer hair cells, supporting cells, striae vascularis and spiral ganglions were damaged. In the third group, ABR hearing threshold elevated markedly. All above-mentioned cells were severely damaged. The experiment showed that the cochlear damage induced by DDP was dose related. The severest damage was seen in the second turn of the cochlea. The damage to the Deiters' cells was earliest and severest. The outer hair cells were more vulnerable to the damage than the inner hair cells did.

Animals↗
PubMed1989

Vasopressin-induced transfer via light vesicles of receptors and water channels from basolateral to apical membrane of toad bladder.

Toad bladder epithelial cells were homogenized and fractionated by Percoll density-gradient centrifugation. Binding of tritium-labeled vasopressin ([3H]AVP) was measured in surface membranes (SM), microsomes (M), and a 100,000 g (60-min) microsomal supernatant fraction (S). More than two-thirds of the total receptors were in S. Receptors in SM--but not in S--were tightly coupled to G-protein as suggested by inhibition of [3H]AVP binding by GTP. GTP-sensitivity of [3H]AVP binding was not altered by vasotocin (AVT) stimulation, although the distribution of receptors shifted from SM to S. Intact bladders, exposed on the serosal side to 1-desamino, 7-lysine-(4-azidobenzoyl), 8-arginine vasotocin (d7-N3-AVT) in the presence of UV light, exhibited a persistent hydroosmotic response compared to controls stimulated with photoaffinity analog in the dark. Cell fractions from the irradiated bladders showed a reduction in [3H]AVP binding in SM and S. Intact bladders, exposed on the mucosal side to d7-N3-AVT in the presence of UV light (while stimulated from the serosal side with AVP) exhibited a decrease in [3H]AVP binding in SM compared to controls without d7-N3-AVT.(ABSTRACT TRUNCATED AT 250 WORDS)

Affinity Labels↗
PubMed1987

Covalent labeling of hydrosmotic toad bladder receptors with an antagonist of vasotocin.

A photoreactive analogue of vasotocin, [1-desamino,4-lysine(azidobenzoyl),8-arginine]vasotocin (4-N3-AVT), has been examined in the isolated toad urinary bladder for biological activity and binding to hormonal receptors. Although 4-N3-AVT induced only a small increase in bladder permeability to water, it behaved as a potent inhibitor of hydrosmotic action of [8-arginine]vasotocin (AVT) and [8-arginine]vasopressin (AVP). The inhibitory action of 4-N3-AVT was readily reversed on removal of the analogue from the serosal bathing solution. On the other hand, when bladders were exposed to 4-N3-AVT in the presence of long wavelength UV light (365 nm), the inhibition by 4-N3-AVT was not reversed on washout of the analogue. The dose of vasopressin required for a half-maximal response (ED50 value) was increased from 5 X 10(-9) to 1.3 X 10(-7) M in bladders photolabeled with 4-N3-AVT and the maximal response capacity of the tissue (intrinsic activity) was reduced to 79% of nonphotolabeled controls. A crude membrane preparation derived from bladders photolabeled with 4-N3-AVT contained 72 fmol of specific binding sites for tritium-labeled vasopressin per milligram protein, whereas nonphotolabeled controls had 136 fmol of specific binding sites per milligram protein. These observations suggest that 4-N3-AVT forms a covalent bond with hydrosmotic receptors in the presence of UV light. This is the first antagonistic photoaffinity analogue observed in the toad bladder and it may serve as a useful tool for analyzing the cellular mechanism of action of antidiuretic hormone.

Animals↗
PubMed1987

Synthesis and biological activities of a photoaffinity probe for vasotocin receptors.

This study reports the synthesis and biological activities of 1-desamino, 7-lysine-(4-azidobenzoyl), 8-arginine vasotocin (d7-N3-AVT). This compound was found to be biologically active in the rat antidiuretic assay (20 U/mg), to behave as an antagonist of vasopressin in the rat pressor assay (pA2 = 6.6), and to yield a half-maximal hydroosmotic response in the isolated toad urinary bladder at a bath concentration of 2.4 X 10(-8) M. When toad bladders were exposed to d7-N3-AVT in the presence of long wavelength UV light, the hydroosmotic response persisted in spite of prolonged and repeated periods of washout. By contrast, the hydroosmotic response in control bladders after stimulation with d7-N3-AVT in the absence of UV irradiation was fully reversed within 15 min of washout. A membrane preparation derived from bladders that had been photolabeled with d7-N3-AVT and washed for 1 h specifically bound 325 fmol [3H]vasopressin/mg protein. Matched bladders exposed to the analog in the absence of UV irradiation and washed for 1 h specifically bound 591 fmol [3H]vasopressin per mg of protein. These studies indicate that d7-N3-AVT binds covalently to hydroosmotic receptors of toad urinary bladder and forms a complex that is functional in triggering an increase in the permeability to water of the epithelium. This analog may prove useful in the isolation and purification of vasotocin receptors in lower vertebrates.

Affinity Labels↗
PubMed1986

Occurrence of donor Langerhans cells in mouse and rat chimeras and their replacement in skin grafts.

Evidence is presented that some endogenous Langerhans cells (LCs) may persist indefinitely in skin grafts. This evidence is based on the observation that although 2 weeks after grafting F1 hybrid mice and rats with genetically compatible skin, most of the LCs in the grafts were replaced with those of the host, some LCs of graft origin persisted for as long as the grafts were followed (154 days in mice and 249 days in rats). It has also been demonstrated that the spleen may be as good a source of LCs as the marrow. Thus, 6 weeks after lethally irradiated mice were restored with F1 hybrid spleen cells, most of the LCs in the epidermis of their pinnae were of donor origin. LCs of donor origin also were found in the epidermis of the pinnae of animals that had been inoculated at birth with spleen and lymph node cells (mice) or bone marrow cells (rats). Hence the occurrence of these cells provides another means of confirming that tolerance (chimerism) has been induced.

Animals↗
PubMed1986

Downregulation of vasopressin receptors in toad bladder.

Binding of tritium-labeled vasopressin [( 3H]AVP) to a broken epithelial cell preparation of the toad's urinary bladder has been related to hormonal action on water and urea transport across the intact tissue. Hormone binding to receptor sites and permeability changes were initiated at the same concentration of hormone (0.4 nM). Half-maximal urea and water permeability responses were observed with 3.1 and 5.6 nM AVP, respectively, although half-maximal receptor saturation required considerably higher concentrations of hormone (less than 500 nM). Because maximal permeability responses were obtained with occupation of approximately 200 fmol/mg protein receptor sites and the total receptor density was in excess of 2,000 fmol/mg protein, there is apparently a receptor reserve in this tissue. The antidiuretic hormone employed by the toad is vasotocin (AVT). This compound was 60-fold more effective than AVP in displacing [3H]AVP from receptor sites. Preincubation of bladders with AVT resulted in downregulation of receptor sites. Although the magnitude of receptor loss was equivalent in the presence or absence of a transmembrane osmotic pressure gradient, the capacity of AVT to induce permeability changes was more markedly reduced in the presence of an osmotic gradient. This observation suggests that the negative-feedback signal initiated by water flow through the hormone target cell diminishes sensitivity to hormone by a mechanism other than by a reduction in the number of surface receptors or by a decrease in their affinity for the hormone.

Animals↗
PubMed1986

Vasopressin binding sites in toad bladder: studies with the photoaffinity analogue [Phe(p-N3)3]AVP.

Toad bladders were exposed to [Phe(p-N3)3]AVP (N3-AVP), an analogue of vasopressin with a photoreactive p-azido group in position three, in the presence and absence of ultraviolet (UV) light. Bladders exposed to the analogue in the presence of UV light showed an increase in membrane permeability to water, which persisted in spite of repeated and prolonged washout of analogue. In contrast, the hydroosmotic response induced by the analogue in the absence of UV light was readily reversed on washout. Aliquots of a broken epithelial cell preparation, derived from bladders that had been exposed to the analogue in the presence of UV light, bound less tritium-labeled vasopressin ([3H]AVP) than control aliquots that had been exposed to the analogue in the absence of UV irradiation or irradiated in the absence of the analogue. Membrane preparations that had not been photolabeled had specific binding sites for [3H]AVP in excess of 1,800 fmol/mg protein without evidence of saturation at a [3H]AVP concentration of 250 nM. Conversely, photolabeled membranes were saturated at a [3H]AVP concentration of 100 nM. The present studies demonstrate that a high proportion of [3H]AVP binding sites can be covalently labeled with N3-AVP and that at least some of these N3-AVP-bound sites are functional in triggering an increase in membrane permeability to water.

Affinity Labels↗