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C C Chang

Publications and source records attributed to C C Chang.

At least 541 records · Page 30Linked to original sources
PubMed1985

Acetylcholine hydrolysis during neuromuscular transmission in the synaptic cleft of skeletal muscle of mouse and chick.

Inhibition of acetylcholinesterase (AChE) by more than 80% by neostigmine or physostigmine resulted in a failure of tetanic contraction (100 Hz) in the isolated mouse nerve-diaphragm preparation. In the chick biventer cervicis muscle, however, the tetanic contraction was well maintained and even outlasted the period of nerve stimulation after inactivation of AChE. The concentration of (+)tubocurarine for 70% block of the indirect twitch response of the mouse diaphragm at 0.1 Hz was increased from 0.67 to 0.99 to 1.21-2.03 microM in the presence of neostigmine (0.15-1.5 microM) which inhibited AChE by 70% or more, while that to depress the tetanic contraction (50 Hz) was increased from 0.38 to 0.42 to 0.53-0.69 microM. In the chick muscle, physostigmine at 2.4 microM increased the concentration of (+)tubocurarine for 70% block of the twitch response from 1.68 to 4.14 microM, whereas that for block of the response to exogenous acetylcholine (ACh) was increased from 1.47 to 74.6 microM. On single stimulation, the relative peak concentrations of acetylcholine (ACh) at the postsynaptic receptor site of the mouse diaphragm and chick biventer cervicis were estimated to be increased by about 110 and 120% respectively, after complete inhibition of AChE. In the chick muscle, physostigmine increased the relative concentration of ACh by about 40-fold at the receptor site for exogenously applied ACh. It is concluded that the intrinsic ACh released from the nerve terminal is hydrolyzed by about 50% during the time of diffusion across the synaptic cleft whereas most of exogenous ACh is hydrolyzed before reaching the target.

Acetylcholine↗
PubMed1985

Electrophysiological studies of myotoxin a, isolated from prairie rattlesnake (Crotalus viridis viridis) venom, on murine skeletal muscles.

Myotoxin a reduced the resting membrane potential of mouse and rat diaphragms from about -80 mV to -60 mV, induced spontaneous repetitive firing and enhanced the contractile force in response to single stimulations. The depolarizing effect was reversed noncompetitively by tetrodotoxin, local anesthetics or low Na+ solution, but was augmented by ouabain or low Cl-solution while being unaffected by high K+ solution or electrical stimulation of the muscle. The duration of muscle action potential was prolonged by only 20-30%, whereas the rate of rise (dV/dt) was unaffected. About a 40% increase of membrane conductance was observed, be abolished by the Na+-channel blocker tetrodotoxin. By contrast, K+ conductance was unaffected. Effects on caffeine-induced contracture, quantal release of neurotransmitter and the amplitude of miniature endplate potential were not appreciably affected. These effects of myotoxin a indicate that the toxin affects the muscle, but not the nerve, by acting specifically on the Na+-channel of the sarcolemma or T-tubule, like crotamine, rather than on the sarcoplasmic reticulum. The effects of sea anemone toxin II on the Na+-channel (marked depolarization and prolongation of action potential) could not be prevented by saturating the muscle with myotoxin a. On the other hand, the effect of veratridine, a member of another group of toxins acting on the Na+-channel, was enhanced. These results suggest that myotoxin a acts on the Na+-channel at a site which is discrete from those of tetrodotoxin, veratridine and sea anemone toxin II.

Action Potentials↗
PubMed1985

Formulation of a potential antipregnancy vaccine based on the beta-subunit of human chorionic gonadotropin (beta-hCG). I. Alternative macromolecular carriers.

The antibody response obtained after vaccinating rabbits with the beta-subunit of human chorionic gonadotropin (beta-hCG) linked to several protein and polysaccharide carriers was measured. In all but one preparation, carbodiimide was used to couple the beta-hCG to the carrier. Tetanus toxoid (TT) and cholera vaccine proved the most effective carriers among those examined. TT from different manufacturers proved to be greatly different in free amino group content and differed in ability to participate in the coupling reaction. Reasonably good replication of the coupling reaction was obtained with different production lots from the same manufacturer. Inferior antigenic response was obtained with the products of coupling beta-hCG to H. pertussis, influenza vaccine, polylysine, pneumococcus polysaccharide, or E. coli polysaccharide. The findings indicate TT and cholera vaccine to be especially effective in enhancing the antigenicity of a weakly antigenic peptide but point to significant differences in the TT from different manufacturers.

Adjuvants, Immunologic↗
PubMed1985

Formulation of a potential antipregnancy vaccine based on the beta-subunit of human chorionic gonadotropin (beta-hCG). II. Use of compounds of the muramyl dipeptide (MDP) family as adjuvants.

Earlier tests of an antipregnancy vaccine consisting of the beta-subunit of human chorionic gonadotropin (beta-hCG) linked by reaction with a carbodiimide reagent to tetanus toxoid (TT) and adsorbed on Al(OH)3 resulted in antibody responses that were judged inadequate in some women. Experiments were therefore conducted to evaluate the effectiveness of additional adjuvants in increasing the antibody response. Muramyl dipeptide (MDP) and several of its analogs were formulated with the vaccine and tested in rabbits. Some of the analogs, and notably N-acetyl-normuramyl-L-alanyl-D-isoglutamine, elicited substantial increments in the ability of the antisera to bind [125I]hCG and in its ability to neutralize hCG in the rat uterine weight assay. The effectiveness of these peptides was greatest when formulated in a water-in-oil emulsion. Increments of 10 fold were attained using a vegetable oil as the oil component. The MDP analogs were much less effective as adjuvants when formulated in oil-in-water emulsions or in aqueous suspensions of the antigen. It is concluded that selected MDP analogs incorporated in a water-in-vegetable oil emulsion can markedly increase the circulating antibody response to the beta-hCG-TT vaccine.

Acetylmuramyl-Alanyl-Isoglutamine↗
PubMed1985

Formulation of a potential antipregnancy vaccine based on the beta-subunit of human chorionic gonadotropin (beta-hCG). III. Evaluation of various vehicles and adjuvants.

Rabbits were used to test the efficacy of several materials as supplementary adjuvants when administered as part of a vaccine formulation consisting of the beta-subunit of human chorionic gonadotropin linked to tetanus toxoid (beta-hCG-TT) and adsorbed on Al(OH)3. In the amounts used, Corynebacterium parvum, levamisole, thymic factor, and N,N-dioctadecyl-N',N'-bis(2-hydroxyethyl)propanediamine exhibited little adjuvant activity although the latter material elicited marginal increments when incorporated in liposomes. A Salmonella lipopolysaccharide preparation (SPLPS) and a streptococcal preparation (OK-432) each gave approximately 7-fold increments in titer. The SPLPS preparation was pyrogenic at the doses used. OK-432 was nonpyrogenic and did not cause other evident undesirable effects. It may therefore prove to be a useful adjuvant. It gave a nearly flat dose response curve over the range of 0.5 to 4.0 mg per rabbit. Incorporation of beta-hCG-TT on Al(OH)3 in a water-in-oil emulsion caused a moderate increase in titers. Incorporation into liposomes or an oil-in-water emulsion was not effective.

Adjuvants, Immunologic↗
PubMed1985

Potential role of the src gene product in inhibition of gap-junctional communication in NIH/3T3 cells.

The effects of the src gene on the activity of protein kinase C and intercellular communication have been studied in transformed NIH/3T3 clones isolated from soft agar following transfection with the plasmid carrying the v-src gene (psrc-11). Six transformed clones that were studied contained newly incorporated v-src genes in the genome, had an increased amount of pp60src, and showed enhanced activities of protein kinase C. Intercellular communication, studied by observing with autoradiography the transfer of [3H]uridine nucleotide from prelabeled donor cells to recipient cells in contact, was found to be reduced in transformed clones as compared to parental NIH/3T3 cells. Treatment with phorbol 12-myristate 13-acetate was also found to increase protein kinase C activity and to reduce intercellular communication in normal NIH/3T3 cells. These results suggest that the v-src gene product, in a manner similar to some of the powerful tumor promoters, may directly or indirectly affect cell-cell communication.

Animals↗
PubMed1985

Allelic polymorphism and transassociation of molecules encoded by the HLA-DQ subregion.

A monoclonal antibody, CC11.23, with monomorphic specificity predominantly for products of the HLA-DQ subregion, has been used to demonstrate primary structural variation among DQ molecules. Two cell lines of each haplotype (DR1-7) were radiolabeled with [3H]tyrosine. alpha and beta chains were isolated from CC11.23-reactive preparations, and their amino-terminal tyrosine sequences were determined. Each DR haplotype (with the exception of DRw6) was found to express a distinct DQ molecule with a minimum of three allelic forms of the DQ alpha chain and five allelic forms of the DQ beta chain. At the primary structural level, the locus for the DQ beta chain appears to be as polymorphic as the locus for the DR beta chain. Unlike the locus for the DR alpha chain (which is essentially nonpolymorphic), the locus for the DQ alpha chain was found to be polymorphic. Comparison of DQ molecules from two different heterozygous cell lines with those from homozygous cell lines revealed that in heterozygotes, DQ alpha chains from either allele can associate with DQ beta chains from one allele. The formation of hybrid HLA-DQ molecules by both cis and trans gene complementation, coupled with several polymorphic forms of each of the DQ subunits, considerably increases the repertoire of DQ alloantigens in heterozygotes.

Alleles↗
PubMed1985

Further characterization of the in vitro assay for inhibitors of metabolic cooperation in the Chinese hamster V79 cell line.

12-O-Tetradecanoylphorbol-13-acetate (TPA) has been previously shown to inhibit metabolic cooperation in Chinese hamster V79 cells. An in vitro assay, based on this phenomenon, has been developed to study tumor promoters. Several parameters concerning the metabolic cooperation assay using V79 Chinese hamster cells were further investigated in this report. Pretreatment of the cells with TPA in situ for different periods of time did not result in any detectable change in the inhibition of metabolic cooperation. If cells were replated after TPA treatment, a different result was obtained. There was an apparent decrease in the ability of TPA to inhibit metabolic cooperation when TPA was added back to the TPA-pretreated cultures. However, when TPA was omitted from the TPA pretreated cultures after replating, the inhibition of metabolic cooperation remained high. It was also found that pretreatment of the cells with another chemical, aldrin, exhibited the same pattern as the in situ TPA pretreatment effect on inhibition of metabolic cooperation. In order to obtain a high level of inhibition of metabolic cooperation when using aldrin in this assay, it was determined that the chemical needed to be present for more than one day. Our studies also showed that a 24 h treatment with 6-thioguanine did not kill 6-thioguanine-sensitive cells quickly, nor did it prevent them from performing metabolic cooperation. The relationship of cell density and TPA concentration was also studied. It was observed that a higher cell density required higher TPA concentration to inhibit, maximally, metabolic cooperation. A 'down regulation' type effect was noted when culture was challenged with different concentrations of TPA. These results were interpreted to be consistent with the hypothesis that inhibited gap-junctional intercellular communication is one of the components of tumor promotion.

Aldrin↗
PubMed1985

Localization of cytokinin biosynthetic sites in pea plants and carrot roots.

The biosynthesis of cytokinins was examined in pea (Pisum sativum L.) plant organs and carrot (Daucus carota L.) root tissues. When pea roots, stems, and leaves were grown separately for three weeks on a culture medium containing [8-(14)C]adenine without an exogenous supply of cytokinin and auxin, radioactive cytokinins were synthesized by each of these organs. Incubation of carrot root cambium and noncambium tissues for three days in a liquid culture medium containing [8-(14)C]adenine without cytokinin demonstrates that radioactive cytokinins were synthesized in the cambium but not in the noncambium tissue preparation. The radioactive cytokinins extracted from each of these tissues were analyzed by Sephadex LH-20 columns, reverse phase high pressure liquid chromatography, paper chromatography in various solvent systems, and paper electrophoresis. The main species of cytokinins detectable by these methods are N(6)-(Delta(2)-isopentyl_adenine-5'-monophosphate, 6-(4-hydroxy-3-methyl-2-butenyl-amino)-9-beta-ribofuranosylpurine-5'- monophosphate, N(6)-(Delta(2)-isopentenyl)adenosine, 6-(4-hydroxy-3-methyl-2-butenylamino)-9-beta-ribofuranosylpurine, N(6)-(Delta(2)-isopentenyl)adenine, and 6-(4-hydroxy-3-methyl-2-butenylamino)purine. On the basis of the amounts of cytokinin synthesized per gram fresh tissues, these results indicate that the root is the major site, but not the only site, of cytokinin biosynthesis. Furthermore, cambium and possibly all actively dividing tissues are responsible for the synthesis of this group of plant hormones.

Journal Article↗
PubMed1985

A candidate carrier protein for beta-human chorionic gonadotropin: 54,000-molecular-weight fragment of tetanus toxin.

As an alternative to intact tetanus toxoid as a carrier for beta-human chorionic gonadotropin (beta-hCG), a fragment of tetanus toxin was sought that had a relatively low molecular weight, yet was highly immunogenic. Purified culture filtrate tetanus toxin was subjected to limited enzymatic digestion with papain, and the resulting fragments separated by column chromatography on Sephadex G-150. Four fractions were thus identified. Fraction II was found to have a molecular weight of 54,000 by SDS-polyacrylamide gel electrophoresis. This fragment was covalently linked to the beta-subunit of hCG (beta-hCG-TTII) using carbodiimide hydrochloride. The ability of beta-hCG-TTII to stimulate production of anti-hCG sera in rabbits was measured by 125I-hCG radioimmunoassay. At sera dilutions of 1:40,000, an average 125I-hCG binding capacity of 34.7 +/- 5.86% (mean +/- SD) was observed 8 weeks after the final immunization. Tetanus toxin Fragment II has the potential for future application in active immunization studies involving hormone-carrier conjugates.

Animals↗
PubMed1985

Congenital bronchobiliary fistula.

Congenital bronchobiliary fistula is a rare cause of respiratory distress in newborn infants and should be included in the differential diagnosis of aspiration pneumonia. A 1-week-old infant was examined using selective bronchography of the fistula and is the youngest successfully treated patient described thus far.

Biliary Fistula↗