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Biomedical subjects

H H Chang

Publications and source records attributed to H H Chang.

At least 73 records · Page 4Linked to original sources
PubMed1983

High affinity Ca2+-stimulated Mg2+-dependent ATPase in rat brain synaptosomes, synaptic membranes, and microsomes.

High affinity Ca2+-stimulated Mg2+-dependent ATPase activity of nerve ending particles (synaptosomes) from rat brain tissue appears to be associated primarily with isolated synaptic plasma membranes. The synaptic membrane (Ca2+ + Mg2+)-ATPase activity was found to exhibit strict dependence on Mg2+ for the presence of the activity, a high affinity for Ca2+ (K0.5 = 0.23 microM), and relatively high affinities for both Mg2+ and ATP (K0.5 = 6.0 microM for Mg2+ and KM = 18.9 microM for ATP). These kinetic constants were determined in incubation media that were buffered with the divalent cation chelator trans-cyclohexane-1,2-diamine-N,N,N',N'-tetraacetic acid. The enzyme activity was not inhibited by ouabain or oligomycin but was sensitive to low concentrations of vanadate. The microsomal membrane subfraction was the other brain subcellular fraction with a high affinity (Ca2+ + Mg2+)-ATPase activity which approximated that of the synaptic plasma membranes. The two membrane-related high affinity (Ca2+ + Mg2+)-ATPase activities could be distinguished on the basis of their differential sensitivity to vanadate at concentrations below 10 microM. Only the synaptic plasma membrane (Ca2+ + Mg2+)-ATPase was inhibited by 0.25-10 microM vanadate. The studies described here indicate the possible involvement of both the microsomal and the neuronal plasma membrane (Ca2+ + Mg2+)-ATPase in high affinity Ca2+ transport across membranes of brain neurons. In addition, they suggest a means by which the relative contributions of each transport system might be evaluated based on their differential sensitivity to inhibition by vanadate.

Animals↗
PubMed1983

Ethanol effects on synaptic glutamate receptor function and on membrane lipid organization.

The enhancement of L-glutamic acid binding activity of brain synaptic membranes by low concentrations of ethanol (less than 50 mM) and the decrease in binding at high concentrations (greater than 100 mM) was not due to a direct action by ethanol on the glutamate binding protein. Biphasic effects of ethanol on membrane protein complexes such as the glutamate binding sites might be the result of biphasic changes in membrane lipid organization. Low ethanol concentrations (0.1-4.0 mM) were shown to decrease fatty acid chain motion detected by the EPR probe 5-doxyl stearic acid, whereas high concentrations (greater than 400 mM) increased lipid motion in egg phosphatidylcholine liposomes. The function of the L-glutamate receptor-ion channel complex in the presence of ethanol was also determined by measuring the changes in thiocyanate (SCN-) influx brought about by L-glutamate or ethanol. A low concentration of ethanol (9.4 mM) diminished the L-glutamate-induced depolarization of synaptic membranes, while a high concentration (93.7 mM) increased the passive SCN-influx and produced a transient overshoot in glutamate-stimulated SCN-flux.

Animals↗
PubMed1982

L-Glutamate effects on electrical potentials of synaptic plasma membrane vesicles.

The electrogenic nature of the L-glutamate-stimulated Na+ flux was examined by measuring the distribution of the lipophilic anion [35S]thiocyanate (SCN-) into synaptic membrane vesicles that were incubated in a NaCl medium. Concentrations of L-glutamate from 10(-7) to 10(-4) M added to the incubation medium caused an enhanced intravesicular accumulation of SCN-. Based on the SCN- distribution in synaptic membrane vesicles it was calculated that 10 microM L-glutamate induced an average change in the membrane potential of + 13 mV. L-Glutamate enhanced both the Na+ and K+ conductance of these membranes as determined by increases in SCN- influx. Other neuroexcitatory amino acids and amino acid analogs (D-glutamate, L-aspartate, L-cysteine sulfinate, kainate, ibotenate, quisqualate, N-methyl-D-aspartate, and DL-homocysteate) also increased SCN- accumulation in synaptic membrane vesicles. These observations are indicative of the activation by L-glutamate and some of its analogs of excitatory amino acid receptor ion channel complexes in synaptic membranes.

Animals↗
PubMed1982

Differential effects of metal ligands on synaptic membrane glutamate binding and uptake systems.

The high affinity, Na+-independent L-[3H]glutamate binding process in synaptic membranes and in the purified binding protein was shown to be inhibited to an almost equal extent by the metal ligands NaN3, KCN, and o-phenanthroline, and by 2,4,5-trihydroxyphenylalanine (6-OH DOPA). The high affinity, Na+-dependent glutamate transport activity in these membranes was almost totally insensitive to NaN3, o-phenanthroline, KCN, and 6-OH DOPA. These agents, especially 6-OH DOPA, may be useful tools in achieving a discrimination between putative physiologic receptors and uptake carrier sites for L-glutamate in synaptic membranes. The sensitivity of the glutamate binding sites to the effects of the metal ligands may be correlated to the presence of an iron-sulfur center in the purified glutamate binding protein. some of the characteristics of this metallic center were explored by optical and paramagnetic resonance spectroscopic techniques and are described in this study.

Animals↗
PubMed1982

Sudden death in young athletes.

The sudden, unexpected death of four young athletes and the findings in their hearts at the time of necropsy were studied. Two athletes had anomalous left coronary origin from the anterior valsalva's sinus. In these cases, the sharp left-ward passage of the coronary artery along the aortic wall may cause the entrance into the left coronary system to be slit-like. There may be an increased expansion of the pulmonary artery and aorta with increased cardiac activity during exercise. Consequently, the left coronary artery may stretch and form a flap-like closure of the orifice of the left coronary, with sudden, fatal myocardial ischemia. The third young athlete had hypertrophic cardiomyopathy that could account for his sudden death; however, the cause of sudden death of the fourth could not be explained despite careful studies.

Adolescent↗
PubMed1981

L-glutamate stimulation of Na+ efflux from brain synaptic membrane vesicles.

The characteristics of 22Na efflux from 22NaCl-preloaded synaptic plasma membrane vesicles and the stimulation of such efflux by gramicidin D and L-glutamate were determined. The rate and magnitude of passive Na+ efflux were dependent on the initial intravesicular NaCl concentration. A Na+:cation exchange process was also observed. Gramicidin D markedly enhanced Na+ efflux in a concentration-dependent manner and at 10 microM it caused total loss of intravesicular 22Na. The neuroexcitatory amino acids L-glutamate and D-glutamate, and the amino acid analog kainic acid, also stimulated Na+ efflux in a dose-dependent fashion, but their effects were weaker than those of gramicidin D. The mechanism of glutamate stimulation of Na+ flux is presumed to be through the activation of the glutamate receptor . Na+ channel complex in these membranes.

Animals↗
PubMed1981

Biochemical-molecular characteristics of the brain synaptic membrane glutamate receptor.

The studies described above have provided evidence for the presence of a high affinity, glutamate binding glycoprotein which has some of the pharmacologic characteristics of the recognition site of neuronal glutamate receptors. In addition, evidence was presented for the distinct molecular nature of this glutamate binding protein as compared to that of the kainic acid binding macromolecule in synaptic membranes and also, for the differential characteristics of the glutamate binding sites as compared to the glutamate transport carriers. Finally, information was presented which is suggestive of the presence and functional integrity of glutamate receptor.ion channel complexes in synaptic membrane preparations.

Animals↗
PubMed1979

Effect of phospholipase A2 on purified gastric vesicles.

The phospholipid and fatty acid composition and role of phospholipids in enzyme and transport function of gastric (H+ + K+)-ATPase vesicles was studied using phospholipase A2 (bee venom). The composition (%) was phosphatidyl-choline (PC) 33%; sphingomyelin (sph) 25%; phosphatidylethanolamine (PE) 22%; phosphatidylserine (PS) 11%; and phosphatidylinositol (PI) 8%. The fatty acid composition showed a high degree of unsaturation. In both fresh and lyophilized preparations, even with prolonged incubation, only 50% of phospholipids were hydrolyzed, but the amount of PE and PS disappearing was increased following lyophilization. There was a marked decrease in K+-ATPase activity (75%) but essentially no loss of the associated K+ p-nitrophenyl phosphatase was found. ATPase activity could be largely restored by various phospholipids (PE greater than PC greater than PS). There was also an increase in Mg2+-ATPase activity, partially reversed in fresh preparations by the addition of phospholipids (PE greater than PS greater than PC). Proton transport activity of the preparation was rapidly inhibited, initially due to a large increase in the HCl permeability of the preparation. Associated with these enzymatic and functional changes, the ATP-induced conformational changes, as indicated by circular dichroism spectra were inhibited.

Adenosine Triphosphatases↗
PubMed1979

Characterization of gastric mucosal membranes. X. Immunological studies of gastric (H+ + K+)-ATPase.

Gastric mucosal homogenates from hog were fractionated by differential and density gradient centrifugation and free-flow electrophoresis. The two major membrane fractions (FI and FII) thus obtained are distinct both enzymically and in terms of transport reactivity. This heterogenicity extends to their antigenic activity. Purified antibodies which were raised against the K+-ATPase-containing H+ transport fraction FI were of two types: inhibitory and non-inhibitory. Inhibitory antibodies reduced the K+-ATPase activity by approximately 80% and the K+-p-nitro-phenylphosphatase activity by approximately 40% in a concentration-dependent manner, while the small Mg++-dependent component of the enzyme activity was unaffected. Antibodies inhibiting the K+-ATPase also inhibited H+ transport. These antibodies did not cross-react with the other major membrane fraction isolated by free-flow electrophoresis, FII, and gave a single band on rocket immunoelectrophoresis. Antibodies against this FII fraction also did not react with the K+-ATPase and were heterogeneous, giving at least four bands with rocket immunoelectrophoresis and inhibiting both the 5'-nucleotidase and Mg++-ATPase of this fraction. Immunofluorescent staining of tissue sections showed that the FI was derived from the parietal cell of gastric tissue and was localized to the supranuclear area of the cell. Staining of isolated rat gastric cell suspensions by FI antibodies confirmed the selectivity of the antibody and showed a polar, plasma membrane localization. FII antibodies also largely stained the parietal cells in tissue sections. In the 16 hog tissues tested, FI antibodies cross-reacted only with gastric fundus, thyroid and weakly with thymus. Immunoelectronmicroscopy showed that FI antibodies reacted strongly with the secretory membrane at the apical cell surface of the parietal cells and at the secretory canaliculi, weakly with the apical surface of the zymogen cell, and not with the basal-lateral surface of the cells. Thus, the protontranslocating ATPase is localized in the parietal cells and in the region postulated to be the site of acid secretion.

Adenosine Triphosphatases↗
PubMed1979

An acid transporting enzyme in human gastric mucosa.

Isolation of a microsomal fraction from human gastric mucosa followed by density gradient centrifugation yielded a vesicular membrane preparation free of mitochondrial markers, containing a K+-activated, ouabain-insensitive ATPase with an activity of 20.7 mumol P1 released/mg protein per h. Sodium dodecyl sulfate gel electrophoresis showed that the human gastric membrane vesicles contained a major polypeptide of 110,000 daltons, which accounted for approximately or equal to 30% of the total protein stained and was phosphorylated by [gamma-32P]ATP and dephosphorylated in the presence of K+. Electron microscopy revealed the presence of vesicles with an average size of 0.13 micrometer in diameter. Addition of 0.65 microM ATP to this vesicular preparation resulted in the uptake of 17 nmol H+/mg protein which was dependent on the presence of K+. The gradient was dissipated by a combination of valinomycin and protonophore after consumption of the ATP. Incubation of fixed human fundic sections or human gastric biopsy with monospecific hog gastric membrane antibody followed by fluorescein-conjugated goat anti-rabbit gamma-globulin, showed fluorescent staining in the middle portion of the gastric glands. These data indicate that human stomach contains a H+ transport ATPase with characteristics similar to those established for lower species.

Adenosine Triphosphatases↗
PubMed1979

Comparative study of two methods for extraction of aflatoxin from peanut meal and peanut butter.

The difference between the CB and Best Foods methods in extracting aflatoxins from peanut products has been studied. The CB method yields 60, 121, 35, and 22% higher results for aflatoxins B1, B2, G1, and G2, respectively for 4 samples of peanut meal and 6 samples of peanut butter studied. Both reverse phase liquid chromatography and thin layer chromatography were used to quantitate the extracted aflatoxins.

Aflatoxins↗
PubMed1977

Radioactive conversion products of intramuscularly injected [4-14C]formononetin including sulfates in the urine of hens.

The phytoestrogen formononetin was injected intramuscularly as [4-14C]formononetin into two adult hens. Radioactive materials in the urine for the succeeding 14 days (hen 1) or 16 days (hen 2) were fractionated on DEAE-Sephadex-25 columns by elution with a gradient of NaCl; the four major fractions thus separated were examined by solvent partition, thin-layer chromatography, and enzymic cleavage. The following seven radioactive components were identified in the urine, the average proportions of each being given in terms of percentage of total 14C recovered from the urine: [14C]formononetin (4.3%); [14C]diaidzein (11.4%); [14C]equol (6.8%); [14C]daidzein monosulfate (30.4%); [14C]equol monosulfate (5.8%); [14C]diadzein disulfate (19.8%); and [14C]equol disulfate (6.5%). Small proportions of sulfates of unidentified radioactive phenols were present. Tests for presence of glucosiduronates of 14C-labelled material gave negative results. Radioactive formononetin sulfate was not detected in the urine of either hen.

Animals↗
PubMed1976

A nonelectrogenic H+ pump in plasma membranes of hog stomach.

Differential and density gradient centrifugation were used to prepare a vesicular membrane fraction from hog gastric mucosa enriched 17-fold with respect to cation-activated ATPase and 5'-AMPase. Fractionation of the gradient material by free flow electrophoresis resulted in a fraction 35-fold enriched in cation-activated ATPase and essentially free of 5'-AMPase and Mg2+ATPase. The addition of ATP to either fraction resulted in H+ uptake and Rb+ efflux. The ionophoric and osmotic sensitivity showed that these ion movements were due to transport rather than binding. The cation selectivity sequences, substrate specificities and action of inhibitors indicated that the transport was a function of K+ATPase activity. The characteristics of the ATP-dependent enhancement of SCN- uptake and 8-anilinonapthalene-1-sulfonate fluorescence in the presence of valinomycin and the action of ionophores and lipid-permeable ions suggested that the energy dependent K+:H+ exchange was effectively nonelectrogenic. Thus these vesicles contain a nonelectrogenic (H+ + K+)-ATPase, hence acid secretion by the stomach is probably due to an ATP-dependent H+ + K+ exchange.

Adenosine Triphosphatases↗