Biomedical subjects

G Zhao

Publications and source records attributed to G Zhao.

At least 235 records · Page 13Linked to original sources

PubMed1996

Loss of nitric oxide production in the coronary circulation after the development of dilated cardiomyopathy: a specific defect in the neural regulation of coronary blood flow.

1. The aims of our study were to determine the role of nitric oxide (NO) in cholinergic reflex dilation of the coronary circulation in normal healthy conscious dogs and after the development of pacing-induced dilated cardiac myopathy and overt congestive heart failure. 2. Dogs were instrumented using sterile surgical techniques under general anaesthesia and allowed to fully recover. The Bezold-Jarisch reflex was stimulated by the intra-atrial injection of veratrine or the intravenous injection of PGI2, while the carotid chemoreflex was stimulated by the intracarotid injection of nicotine. Experiments were performed before and after the development of overt congestive heart failure (HF) caused by rapid left ventricular pacing for 4 weeks. 3. The release of NO, or NO-mediated vascular relaxation following administration of acetylcholine (ACh) may have little physiological significance since as ACh is released from nerve endings in vivo. Stimulation of the Bezold-Jarisch or carotid chemoreflex resulted in typical vagal cholinergic reflex coronary vasodilation, an increase in coronary blood flow and a decrease in coronary vascular resistance, which was substantially reduced following NO synthesis inhibition with nitro-L-arginine. 4. After the development of severe congestive HF, the production of NO by sieved coronary microvessels from the heart was markedly reduced accompanied by a 60-80% reduction in both the mRNA (northern blot) and protein (western blot) for endothelial NO synthase in the aorta. 5. After the development of severe pacing-induced HF, activation of the Bezold-Jarisch or carotid chemoreflex no longer resulted in coronary vasodilation due to the disappearance of NO production from the coronary circulation. 6. Therefore, cholinergic reflex coronary vasodilation is mediated by NO. Because coronary blood vessels lose the ability to produce NO after the development of HF, reflex cholinergic coronary vasodilation is markedly altered, uncovering a previously undiscovered specific defect in the integrated control of the coronary circulation in the failing heart.

Animals↗

PubMed1996

A novel alpha-ketoglutarate reductase activity of the serA-encoded 3-phosphoglycerate dehydrogenase of Escherichia coli K-12 and its possible implications for human 2-hydroxyglutaric aciduria.

Escherichia coli serA-encoded 3-phosphoglycerate (3PG) dehydrogenase catalyzes the first step of the major phosphorylated pathway of L-serine (Ser) biosynthesis. The SerA enzyme is evolutionarily related to the pdxB gene product, 4-phosphoerythronate dehydrogenase, which catalyzes the second step in one branch of pyridoxal 5'-phosphate coenzyme biosynthesis. Both the Ser and pyridoxal 5'-phosphate biosynthetic pathways use the serC(pdxF)-encoded transaminase in their next steps. In an analysis of these parallel pathways, we attempted to couple the transaminase and dehydrogenase reactions in the reverse direction. Unexpectedly, we found that the SerA enzyme catalyzes a previously undetected reduction of alpha-ketoglutarate (alpha KG) to 2-hydroxyglutaric acid (HGA). Numerous criteria ruled out the possibility that this SerA alpha KG reductase activity was caused by contamination in the substrate or purified enzyme preparations. HGA was confirmed as the product of the SerA alpha KG reductase reaction by thin-layer chromatography and by enzyme assays showing that both the D- and L-isomers of HGA were substrates for the reverse (dehydrogenase) reaction. Detailed steady-state kinetic analyses showed that alpha KG reduction (apparent Michaelis-Menten constant [Km(app)] = 88 microM; apparent catalytic constant [kcat(app)] = 33.3 s-1) and 3-phosphohydroxypyruvate reduction (Km(app) = 3.2 microM; kcatapp = 27.8 s-1), which is the reverse reaction of 3PG oxidation, were the major in vitro activities of the SerA enzyme. The SerA alpha KG reductase was inhibited by Ser, D-HGA, 3PG, and glycine (Gly), whereas the D-HGA dehydrogenase was inhibited by Ser, alpha KG, 3-phosphohydroxypyruvate, and Gly. The implications of these findings for the regulation of Ser biosynthesis, the recycling of NADH, and the enzymology of 2-hydroxyacid dehydrogenases are discussed. Since the same pathway of Ser biosynthesis seems to be present in all organisms, these results suggest that a mutation in the human SerA homolog may contribute to the neurometabolic diseases D- and L-2-hydroxyglutaric aciduria, which lead to the accumulation of D-HGA and L-HGA, respectively.

Alcohol Oxidoreductases↗

PubMed1996

Isolation of a pdxJ point mutation that bypasses the requirement for the PdxH oxidase in pyridoxal 5' -phosphate coenzyme biosynthesis in Escherichia coli K-12.

We isolated 26 suppressor mutations that allowed growth of a delta pdxH::omega null mutant in the absence of pyridoxal. Each suppressor mapped to pdxJ, and the eight suppressors sequenced contained the same glycine-to-serine change in the PdxJ polypeptide. This bypass suppression suggests that PdxJ may participate in formation of the pyridine ring of pyridoxine 5'-phosphate.

Bacterial Proteins↗

PubMed1996

Reduced gene expression of vascular endothelial NO synthase and cyclooxygenase-1 in heart failure.

Endothelium-dependent responses are depressed in coronary and peripheral blood vessels after the onset of pacing-induced heart failure in dogs and heart failure of various etiologies in humans. The present study was designed to examine whether these responses were due to decreases in the expression of endothelial cell NO synthase (ecNOS) and cyclooxygenase-1 (COX-1). After 1 month of left ventricular pacing, 8 mongrel dogs were monitored for heart failure as defined by clinical signs and left ventricular end diastolic pressures > 25 mm Hg. Total RNA and protein were isolated from endothelial cells scraped from the thoracic aorta and analyzed by Northern and Western blotting, respectively. Blots probed with 32P-labeled cDNAs for ecNOS and COX-1 were quantified densitometrically, and results were normalized against GAPDH or von Willebrand factor (vWF). In arbitrary units, the ratios of ecNOS to GAPDH were 2.66 +/- 0.77 (mean +/- SEM, n = 17) and 1.12 +/- 0.37 (n = 6 and the ratios of COX-1 to GAPDH were 1.52 +/- 0.52 and 0.56 +/- 0.15 before and after heart failure, respectively. These represent 56% to 64% (P < .05) reductions in ecNOS and COX-1 gene expression. There was no change in the ratios of either COX-1 or ecNOS to vWF. There was also a marked reduction in ecNOS protein after heart failure, estimated at 70%. A marked reduction in nitrite production, a measure of enzyme activity, from thoracic aortas in response to stimulation by either acetylcholine or bradykinin also occurred. To determine whether ecNOS and COX-1 could be independently regulated, an orally active NO-releasing agent, CAS 936, was given to 7 normal dogs for 7 days, and aortic ecNOS and COX-1 mRNAs were analyzed. The ratio of ecNOS to GAPDH was depressed by 52% (P < .05) in aortas from these dogs, whereas the ratio of COX-1 to GAPDH was unchanged. Similar results were found when data were normalized to vWF. These results suggest that at least two endothelial vasodilator gene products are reduced in heart failure, as opposed to a selective defect in NO synthase gene expression.

Animals↗

PubMed1996

Role of endothelium-derived nitric oxide in the modulation of canine myocardial mitochondrial respiration in vitro. Implications for the development of heart failure.

The mechanism responsible for the regulation of cardiac function by endogenous nitric oxide (NO) remains unclear. In this investigation, O2 consumption by freshly isolated myocardial muscle segments from the left ventricular free wall of canine hearts was quantified by a Clark-type O2 electrode at 37 degrees C. S-nitroso-N-acetylpenicillamine (SNAP, 9 +/- 3% to 50 +/- 8%), bradykinin (BK, 14 +/- 3% to 30 +/- 5%), or carbachol (CCh, 15 +/- 4% to 29 +/- 4%) significantly attenuated tissue O2 consumption at doses of 10(-7) to 10(-4) mol/L (mean +/- SE, P < .05). The effects of BK and CCh, but not SNAP, were blocked by 10(-4) mol/L NG-nitro-L-arginine, consistent with both BK and CCh stimulating NO biosynthesis and with SNAP decomposing to release NO, respectively. Similar doses of 8-Br-cGMP caused a respiratory inhibition, but to a lesser extent (9 +/- 2% to 14 +/- 6%). A mitochondrial uncoupler, 2,4-dinitrophenol (at 1 mmol/L), blocked the effects of 8-Br-cGMP, but not those of SNAP, BK, or CCh, suggesting that the major site of action of NO is on mitochondrial electron transport. Myocardial muscle from dogs with pacing-induced heart failure had a basal O2 consumption rate of 251 +/- 21 nmol.min-1.g-1, which was 54% higher than the rate seen in muscle from normal healthy canine hearts. The inhibitory effects of BK and CCh on O2 consumption were not observed in failing cardiac tissue, but SNAP showed an unaltered inhibitory effect. Therefore, our results indicate that NO released from microvascular endothelium by BK, stimulation of muscarinic receptors, and perhaps flow velocity may play an important physiological role in the control of cardiac mitochondrial respiration, and the loss of this regulatory function may contribute to the development of heart failure.

2,4-Dinitrophenol↗

PubMed1996

Interaction between prostacyclin and nitric oxide in the reflex control of the coronary circulation in conscious dogs.

OBJECTIVE: Our goal was to determine the role of nitric oxide (NO) on the coronary vasodilation induced by prostacyclin (PGI2) in conscious dogs. METHODS: Dogs were chronically instrumented for the measurements of coronary blood flow (CBF), left ventricular pressure (LVP), mean arterial pressure (MAP) and heart rate (HR). RESULTS: Intravenous injections of PGI2 caused dose-dependent increases in CBF, and decreases in MAP and late diastolic coronary resistance (LDCR). For instance, CBF increased by 128 +/- 19% (P < 0.05) from 30 +/- 3.5 ml/min and LDCR decreased by 73 +/- 3% (P < 0.05) from 2.57 +/- 0.20 mmHg/ml/min following injection of PGI2 (1.0 microgram/kg). After infusion of nitro-L-arginine (NLA, 35 mg/kg) intravenously, the coronary vasodilation induced by PGI2 was partially attenuated. PGI2 (1.0 microgram/kg) increased CBF by 55 +/- 15% from 33 +/- 5.3 ml/min and decreased LDCR by 42 +/- 9% (both P < 0.05, compared with before NLA) from 3.29 +/- 0.39 mmHg/ml/min. Infusion of L-arginine (100 mg/kg) reversed the action of NLA. For example, PGI2 (1.0 microgram/kg) increased CBF by 115 +/- 15% from 36 +/- 6 ml/min and decreased LDCR by 68 +/- 3% from 3.02 +/- 0.36 mmHg/ml/min (both P > 0.05, compared with before NLA). Atropine (0.1 mg/kg) partially attenuated the coronary vasodilation induced by PGI2 the magnitude of which was almost identical to that by NLA. NLA or atropine also blunted the coronary vasodilation induced by acetylcholine, while the coronary vasodilation induced by nitroglycerin was not affected by NLA. CONCLUSION: Our results indicate that the coronary vasodilation induced by PGI2 was partially attenuated by NLA or atropine, suggesting that the coronary vasodilation induced by PGI2 is due to two components: a reflex parasympathetic cholinergic vasodilation mediated by NO and a direct action of PGI2.

Acetylcholine↗

PubMed1996

The effect of a combined approach to schistosomiasis control on the transmission of Schistosoma japonicum in Xingzi of Poyang Lake area, China.

The impact of a combined approach to schistosomiasis control from 1987 to 1989 and mass chemotherapy from 1992 to 1994 was studied in a rural community in Xingzi county in the northwest corner of Poyang Lake in Jiangxi Province, China. Humans, cattle, buffalo and pigs were known potential reservoirs of Schistosoma japonicum. Transmission occurs during water contact on and around seasonally flooded marshes that are used for grazing, the harvesting of grass and fishing. Humans and livestock underwent yearly selective mass chemotherapy, and snails were eliminated through ploughing and compacting of the marshland in the spring of 1988. Transmission was monitored through the determination of annual re-infection rates in samples of the human population, the annual examination of piles of feces from animals and humans in the marshland, the annual collection and examination of intermediate snail hosts, and the exposure to potentially polluted water and subsequent examination of sentinel mice. Schistosomiasis prevalence among humans and animals declined sharply as soon as mass chemotherapy was implemented. Snail density decreased even before mollusc control was started, possibly indicating a high variability of this indicator. The infection rates of snails and sentinel mice reached zero after a single application of mollusc control. The results underline the importance of single infected water buffalo for the transmission of schistosomiasis. Since the impact stopped for two years (1990-1991), the schistosomiasis prevalence rose quickly. Mass chemotherapy was an effective means to curb the prevalence of schistosomiasis in this area, but the effects were only maintained for one or two years in the marsh zone.

Animals↗

PubMed1996

[Occurrence of depression symptoms and their influence factors in perimenopausal women].

OBJECTIVE: To investigate the prevalence of depression symptoms and their influence factors in perimenopausal women. METHODS: Self-rating depression scale and general condition questionaire were used in 419 perimenopausal women aged 45-55 in Beijing city. RESULTS: The prevalence of depression symptoms in these women was 46.1%, among which 69.9% was mild and 30.1% moderate or severe. The occurrence of depression symptoms in worker group was higher than cadres or skilled person groups (P < 0.01). The incidence of depression symptoms in women with systemic diseases was higher than those without (P < 0.001). Women with decreased libido and dissatisfaction with their husbands, family income and living conditions had a higher incidence than those without (P < 0.05). CONCLUSIONS: The prevalence of depression symptoms in perimenopausal women was considerably high. Clinical doctors should pay attention to psychological problems especially for women with high risks during medical treatment.

Adult↗

PubMed1996

[The effect of immunoregulation of preparation of Mycobacterium vaccea by nitrogen oxide].

OBJECTIVE: Preparation of M. vaccea on synthesis of nitrite [NO2-, an oxidative end product of nitric oxide (NO) synthesis] of peritoneal macrophages by different condition of animals. METHODS: First, the BALB/c mice were immunized by preparation of M. vaccea and effect of synthesis of NO2- by murine peritoneal macrophage was detected. Second, guinea pigs intraperitonealy challenged with M. tuberculosis H37Rv were immunized by preparation of M. vaccea. RESULTS: It was demonstrated that the effect of synthesis of NO2- of the murine peritoneal macrophage of the immunized mice was significantly higher than the unimmunized mice (P < 0.01) and synthesis of NO2- of peritoneal macrophage of challenged guinea pigs immunized with M. vaccea was significantly lower than that of challenged guinea pigs unimmunized with M. vaccea (P < 0.05). CONCLUSION: The preparation of M. vaccea can not only increase the effect of releasing of NO2- of the peritoneal macrophage, but also regulate the effect of immuno-reaction of the animals so as to reduce the damage of the tissue.

Adjuvants, Immunologic↗

PubMed1996

[A study on lens epithelial cell DNA damage induced by hydrogen peroxide in rat and its repair].

OBJECTIVE: The induction and repair of DNA single-strand breaks (SSBs) were measured in primary cultured infant rat lens epithelial cells (RLECs) following hydrogen peroxide (HP) exposure, and the influential factors were detected. METHODS: Utilizing nick translation methodology which utilizes incorporation of labeled nucleotides at the sites of DNA SSBs to sensitively quantitate the damage, we studied the effects of temperature, doses of HP and trace amount of selenium on cell survival. RESULTS: The number of DNA SSBs at 37 degrees was higher than that at 4C (P < 0.01). Significant numbers of SSBs were detected after being insulted by as low as 36.4 mumol/L hydrogen peroxide for 12 minutes 4 degrees (P < 0.05). Repair rapidly initiated and almost completed in 60 minutes after mild damage, and it was unable to repair when the DNA damage was induced by HP at toxic concentration. Trace selenium was added to the culture and incubated for 24 hours, then the number of SSBs was significantly decreased (P < 0.01). CONCLUSIONS: At 37 degrees HP may induce DNA SSBs in RLECs. HP induces the SSBs in a dose dependent manner. The DNA SSBs can not be repaired after severe damage. Trace selenium can decrease the degree of susceptibility to oxidative damage in infant RLECs.

Animals↗

PubMed1996

The repair of eyelid defect with free hard palate mucosal autograft.

OBJECTIVE: To investigate the free hard palate mucosal autograft as a new replacement in eyelid reconstruction. METHODS: (1) Animal experiment, 12 eyelid defects from 3 dogs were repaired with hard palate mucosal autograft, and after operation they had excellent eyelid appearance. The findings of pathological examination, the morphology and thickness of epithelium are the same as its original. The cells and vascularization in the connective tissue are normal. The arrangement of collagen fiber bundles is regular. (2) Clinical practice, 15 eyelid defects from 13 eyes included 3 upper eyelids, 8 lower eyelids and 2 of both upper and lower eyelids. 5 cases were of malignant tumor and 8 cases of trauma. 6 eyelids were of total defect, 4 eyelids of two-third defect and 5 eyelids of a half to one-third defect. The ages ranged from 22 to 79 years old. We used the intermediate split thickness of hard palate mucosal autograft to do the eyelid reconstruction. All the cases were followed for an average of 11.3 months after the reconstruction. RESULTS: 8 eyelid defects were cured, 3 were improved significantly and 4 improved. No severe complications were found. CONCLUSION: The hard palate mucosal autograft acts not only as a palpebral supporting tissue but also forms palpebral conjunctiva.

Adult↗

PubMed1996

[Experimental research and clinical application of homologous dura mater in ocular plastic surgery].

OBJECTIVE: To explore the clinical value of the dura mater implantation in ocular plastic surgeries. METHODS: Alcohol preserved homologous dura mater was implanted into the upper fornix under the conjunctiva of rabbit eye and light, electron microscopic histological and immunological examinations were made for the implant. 38 eyes consisting of 30 eyes of blepharoptosis, 4 eyes of blepharo-coloboma, 3 eyes of hollow socket and 1 eye of teleepicanthus were treated by homologous dura mater implantation. RESULTS: In the follow-up periods ranging from 1.5 to 2.5 years, 26 eyes in the treated eyes were cured, 9 eyes were markedly improved, 3 eyes failed. Histological findings showed that after 1 week of implantation there was cell infiltration around the implant, at 2 weeks new collagenous tissue developed at the margin of the implant and 2-3 months after transplantation, the grafts were replace by the patient's own connective tissue. The histological examination of 3 failure cases showed that the cause of the failure was due to the ischemia of homograft. The results of unidirectional mixed lymphocyte culture showed that the stimulation index before implantation in comparison with that at 96 and 120 hours after implantation had statistical significant differences, while in comparison with that at 144 hours after implantation had no such difference. Before the implantation, the stimulation index of the lymphocyte culture at 96 hours was significantly different from that at 144 hours statistically (P < 0.05). In the comparison of specific killing activity before and after implantation, there was statistical significant difference. CONCLUSION: The effects of transplantation of homologous dura mater employed in ocular plastic surgeries of blepharoptosis, blepharocoloboma, teleepicanthus and hollow socket are fairly good.

Adolescent↗

PubMed1996

[An analysis of diagnostic errors of uveal melanoma].

OBJECTIVE: The causes of erroneous clinical diagnosis of uveal melanomas were studied METHODS: 18 cases with uveal melanoma diagnosed clinically were analyzed by clinical and histopathological methods. RESULTS: The main causes of the misdiagnosis were the opaque media to prevent from a clear view of the fundus in some cases, and clinicians' insufficient experience and ignorance of the case history. The histological bases of the misdiagnosis were suprachoroidal hemorrhage, subretinal hemorrhage and hemorrhage beneath retinal pigment epithelium, organization and formation of scar tissues. CONCLUSION: It is necessary to take the fluorescein angiography preoperatively and perform local resection of tumor on suitable cases.

Adolescent↗

PubMed1995

Chemical vapor deposition fabrication and characterization of silica-coated carbon fiber ultramicroelectrodes.

Carbon fiber disk ultramicroelectrodes (UMEs) with well-defined geometries were prepared by chemical vapor deposition techniques. Transparent silica films with thicknesses from 1 to 600 microns were deposited on the cylindrical length of 5 and 10 microns carbon fibers from a SiCl4, H2, and O2 ternary precursor system at 850-1150 degrees C or sequential deposition from Si(OEt)4 as a single source precursor at 700 degrees C followed by the SiCl4, H2, and O2 precursor system. Film thickness, film adhesion to the fiber substrate, and the overall dimensions of the silica-coated carbon fiber were studied and found to be a function of the precursor system, precursor concentrations, fiber diameter, deposition time, and fiber temperature. The silica films were found to be free of microcracks and characterized by a quality seal between the carbon fiber and the coating. As a result, the silica-coated disk UME exhibits an excellent electrochemical response without the need to use an epoxy sealant at the electrode tip. Furthermore, the deposition of hard and inert ceramic materials imparts durability to fragile carbon fibers and facilitates the handling of UMEs in microenvironments. Finally, the advantage of concentric deposition about the fibers to produce a disk UME in the center of an insulating plane was used to examine the effect of the thickness of the insulating coating on the limiting current response.

Carbon↗

PubMed1995

Selenoperoxidase-dependent glutathione cycle activity in peroxide-challenged leukemia cells.

Murine leukemia L1210 cells rendered deficient in glutathione peroxidase (GPX) and phospholipid hydroperoxide glutathione peroxidase (PHGPX) by Se deprivation (L.Se(-) cells) were found to be more sensitive to tert-butyl hydroperoxide (t-BuOOH) cytotoxicity than Se-replete controls (L.Se(+) cells). Human K562 cells, which express PHGPX, but not GPX, were also more sensitive to t-BuOOH in the Se-deficient (K.Se(-)) than Se-satisfied (K.Se(+)) condition. In examining the metabolic basis for selenoperoxidase-dependent resistance, we found that glucose-replete Se(-) cells reduce t-BuOOH to t-butanol far more slowly than Se(+) cells, the ratio of the first-order rate constants approximating that of the GPX activities (L1210 cells) or PHGPX activities (K562 cells). Monitoring peroxide-induced changes in GSH and GSSG gave consistent results; e.g., glucose-depleted L.Se(+) cells exhibited a first order loss of GSH that was substantially faster than that of glucose-depleted L.Se(-) cells. Under the conditions used, peroxide-induced conversion of GSH to GSSG could be stoichiometrically reversed by resupplying D-glucose, indicating that no significant lysis or GSSG efflux and/or interchange had taken place. The apparent first-order rate constant for GSH decay increased progressively for L1210 cells expressing a range of GPX activities from approximately 5% to 100%, demonstrating that peroxide detoxification is strictly dependent on enzyme content. The initial rate of 14CO2 release from D-[1-14C]glucose supplied in the medium was much greater for L.Se(+) or K.Se(+) cells than for their respective Se(-) counterparts, consistent with greater hexose monophosphate shunt activity in the former. These results highlight the importance of selenoperoxidase action in the glutathione cycle as a means by which tumor cells cope with hydroperoxide stress.

Animals↗

PubMed1995

Selective impairment of vagally mediated, nitric oxide-dependent coronary vasodilation in conscious dogs after pacing-induced heart failure.

BACKGROUND: Activation in conscious dogs of the carotid chemoreflex or cardiac receptors results in coronary vasodilation that is mediated by a vagal cholinergic mechanism. Our previous study showed that the coronary vasodilation following activation of carotid chemoreflex is also mediated by nitric oxide (NO). In addition, NO production is depressed after the development of heart failure. Therefore, we hypothesized that the coronary vasodilation after activation of reflexes that elicit efferent vagal coronary vasodilation would be blunted in conscious dogs after pacing-induced heart failure due to the disappearance of NO. METHODS AND RESULTS: Mongrel dogs were chronically instrumented using sterile techniques for measurements of systemic hemodynamics and left circumflex coronary blood flow (CBF). Without the heart rate controlled, intra-atrial injection of veratrine (4 micrograms/kg) caused bradycardia (-36 +/- 3 beats per minute). With the heart rate controlled, veratrine increased CBF in a dose-dependent manner: for example, 4 micrograms/kg of veratrine increased CBF by 54 +/- 5% from 38 +/- 4.9 mL/min (P < .05). The increases in CBF induced by veratrine were markedly blunted by nitro-L-arginine (NLA). Activation of carotid chemoreflex by nicotine increased CBF by 121 +/- 9% from 32 +/- 4 mL++/min (P < .05) with the heart rate controlled and caused bradycardia (-32 +/- 5 beats per minute) without the heart rate controlled. After the development of heart failure, in response to activation of carotid chemoreflex or cardiac receptors the coronary vasodilation was almost abolished (CBF increased by only 23 +/- 8% or 11 +/- 3%, P < .05 compared with control). There still was a marked bradycardia after injections of nicotine or veratrine (-50 +/- 11 or -48 +/- 7 beats per minute). CONCLUSIONS: Our results indicate that vagally mediated coronary vasodilation is selectively attenuated in conscious dogs after pacing-induced heart failure, whereas the vagally mediated bradycardia is preserved. Since muscarinic receptor-induced coronary vasodilation is mediated by NO, the disappearance of NO from blood vessels leads to a defect in the integrated neural regulation of coronary blood flow and myocardial function during heart failure.

Acetylcholine↗

PubMed1995

Carbon ring-disk ultramicroelectrodes.

Novel ring-disk ultramicroelectrodes (RD-UMEs) with analytical tip diameters as small as 25-30 microns were fabricated. Carbon RD-UMEs were reproducibly prepared by the chemical vapor deposition of alternating concentric layers of silica and carbon on resistively heated 10 microns carbon fibers. High-quality films with excellent adhesion at the interfaces between the carbon and silica layers were shown by electrochemical and scanning electron microscopy measurements. Electrochemical measurements of a solution of 1.0 mM ferrocene with 200 mM LiClO4 in CH3CN were used to characterize the single- and dual-electrode response lf the RD-UME. The electrochemical responses of the ring and the disk are sigmoidal in shape and indicated that radial diffusion is the primary mode of mass transport at each electrode at slow scan rates. Diffusion-controlled generation-collection experiments showed that the concentric dual-electrode configuration exhibits high collection efficiencies at the ring electrode with a 2-5 microns separation between electrodes and a 2-4 microns ring thickness. Close proximity of the ring and disk electrodes led to enhanced detection sensitivity due to back diffusion of regenerated molecules of a reversible redox couple from the collector to the generator electrode.

Carbon↗

PubMed1995

Biochemical characterization of gapB-encoded erythrose 4-phosphate dehydrogenase of Escherichia coli K-12 and its possible role in pyridoxal 5'-phosphate biosynthesis.

One step in de novo pyridoxine (vitamin B6) and pyridoxal 5'-phosphate biosynthesis was predicted to be an oxidation catalyzed by an unidentified D-erythrose-4-phosphate dehydrogenase (E4PDH). To help identify this E4PDH, we purified the Escherichia coli K-12 gapA- and gapB-encoded dehydrogenases to homogeneity and tested whether either uses D-erythrose-4-phosphate (E4P) as a substrate. gapA (gap1) encodes the major D-glyceraldehyde-3-phosphate dehydrogenase (GA3PDH). The function of gapB (gap2) is unknown, although it was suggested that gapB encodes a second form of GA3PDH or is a cryptic gene. We found that the gapB-encoded enzyme is indeed an E4PDH and not a second GA3PDH, whereas gapA-encoded GA3PDH used E4P poorly, if at all, as a substrate under the in vitro reaction conditions used in this study. The amino terminus of purified E4PDH matched the sequence predicted from the gapB DNA sequence. Purified E4PDH was a heat-stable tetramer with a native molecular mass of 132 kDa. E4PDH had an apparent Km value for E4P [Kmapp(E4P)] of 0.96 mM, an apparent kcat catalytic constant for E4P [kcatapp(E4P)] of 200 s-1, Kmapp(NAD+) of 0.074 mM, and kcatapp(NAD+) of 169 s-1 in steady-state reactions in which NADH formation was determined. From specific activities in crude extracts, we estimated that there are at least 940 E4PDH tetramer molecules per bacterium growing in minimal salts medium plus glucose at 37 degrees C. Thin-layer chromatography confirmed that the product of the E4PDH reaction was likely the aldonic acid 4-phosphoerythronate. To establish a possible role of E4PDH in pyridoxal 5'-phosphate biosynthesis, we showed that 4-phosphoerythronate is a likely substrate for the 2-hydroxy-acid dehydrogenase encoded by the pdxB gene. Implications of these findings in the evolution of GA3PDHs are also discussed. On the basis of these results, we propose renaming gapB as epd (for D-erythrose-4-phosphate dehydrogenase).

Alcohol Oxidoreductases↗