The action of local anesthetics on myelin structure and nerve conduction in toad sciatic nerve

X-ray scattering and electrophysiological experiments were performed on toad sciatic nerves in the presence of local anesthetics. In vitro experiments were performed on dissected nerves superfused with Ringer's solutions containing procaine, lidocaine, tetracaine, or dibucaine. In vivo experiments were performed on nerves dissected from animals anesthesized by targeted injections of tetracaine-containing solutions. In all cases the anesthetics were found to have the same effects on the x-ray scattering spectra: the intensity ratio of the even-order to the odd-order reflections increases and the lattice parameter increases. These changes are reversible upon removal of the anesthetic. The magnitude of the structural changes varies with the duration of the superfusion and with the nature and concentration of the anesthetic molecule. A striking quantitative correlation was observed between the structural effects and the potency of the anesthetic. Electron density profiles, which hardly showed any structural alteration of the unit membrane, clearly indicated that the anesthetics have the effect of moving the pairs of membranes apart by increasing the thickness of the cytoplasmic space. Electrophysiological measurements performed on the very samples used in the x-ray scattering experiments showed that the amplitude of the compound action potential is affected earlier than the structure of myelin (as revealed by the x-ray scattering experiments), whereas conduction velocity closely follows the structural alterations.     

Effects of CO2-induced acidification on the fatigue resistance of single mouse muscle fibers at 28 degrees C

The role of reduced muscle pH in the development of skeletal muscle fatigue is unclear. This study investigated the effects of lowering skeletal muscle intracellular pH by exposure to 30% CO2 on the number of isometric tetani needed to induce significant fatigue. Isolated single mouse muscle fibers were stimulated repetitively at intervals of 4-2.5 s by using 80-Hz, 400-ms tetani at 28 degrees C in Tyrode solution bubbled with either 5 or 30% CO2. Stimulation continued until tetanic force had fallen to 40% of the initial value. Exposure to 30% CO2 caused a significant fall in intracellular pH of approximately 0.3 pH unit but did not cause any significant changes in initial peak tetanic force. During the course of repetitive stimulation, intracellular pH fell by approximately 0.3 pH unit in both normal and acidified fibers. The number of tetani needed to reduce force to 40% of the initial value was not significantly different in 5 and 30% CO2 Tyrode. The sole effect of acidosis was to reduce the rate of relaxation of force, especially in fatigued fibers. It is concluded that, at 28 degrees C, acidosis per se does not accelerate the development of fatigue during repeated tetanic stimulation of isolated mouse skeletal muscle fibers.     

Pollution of the work environment by volatile anesthetics and nitrous oxide]

Anaesthetic personnel is exposed to different workload conditions. The individual impact is influenced by external factors and human stress stability. Different symptoms reported to be present in anaesthetic personnel are comparable to symptoms of the sick building syndrome, defined by the WHO in the 90's. They are caused by work-induced distress and the exposure to chemical hazards. In anaesthesia, health defects by anaesthetic vapours and gases have been deplored for many years. After the Russian anaesthesiologist Vaisman published a report in 1967, controlled studies concerning cancerogenicity and teratogenicity of volatile anaesthetics under workspace conditions were carried out. In 1989, time-weighted average exposure threshold limit values of 5 ppm were released in the Federal Republic of Germany for halothane. In 1993 thresholds for enflurane (20 ppm) and nitrous oxide (100 ppm) were released. TLV concentrations for the new anaesthetic agents desflurane and sevoflurane have not yet been defined by authorities. Factors influencing workplace concentrations of anaesthetic gases are the anaesthetic procedures, apparatus leakage, air conditioning, fresh gas flow and the function of the scavenging system. Although cancerogenicity, mutagenicity, teratogenicity and reduction of fertility are discussed as effects of chronic exposure to anaesthetic gases, several review articles doubted the results of studies, finding positive correlations of incidence of occupational disease and the exposure to the volatile and gaseous substances. Mainly coexisting factors like smoke-induced exposure to polybromated biphenyls, disturbance in circadian rhythm, stress and enclosure in narrow exposure systems, increasing teratogenicity and cancerogenicity in animal experiments, are considered to promote unreliability of the studies. All reviewers do not discuss the fact, that all of these co-factors are present in the reality of the anaesthetic workplace. Thus, the studies by Corbett, enthusiastically criticized by different reviewers, simulate the all-day reality of the anaesthetic workplace more precisely than controlled experiments conducted, for example, by Eger and co-workers. The results of animal experiments and retrospective studies therefore do not justify realization of large controlled prospective studies but require the overall revision of the anaesthesiological workplace and the reduction of occupational waste gas exposure to the lowest possible levels below all chronic exposure threshold values.     

The cytotoxic effect of topical mitomycin C on the ciliary body in rabbits]

In order to know the initial lens changes that accompany atopic dermatitis (AD), 99 patients diagnosed dermatologically to have AD without any or with slight external ocular inflammations and with no habit of rubbing the eyelid due to severe itching were examined opthalmologically. Clinically, none of them showed any cataractous changes in their eyes. For the sake of comparison with the above population, 4 AD patients with cataractous eyes, 49 renal transplantation patients who were administered steroids over a long period of time but clinically had no cataractous lenses, and 94 healthy individuals with transparent lenses were also selected as subjects. The crystalline lenses of the subjects were examined using an anterior eye segment analysis system and specular microscopy. From Scheimpflug slit images of the lens, light scattering intensity of different lens layers was measured as an indicator of lens transparency changes. The subcapsular basement membrane and changes in the lens epithelial layers were analyzed from specular images of these areas by image processing. Results and considerations from the investigations were: (1) Initial lens changes in cases with AD which may be occult cataractous findings were often detectable. (2) Cataract associated with AD can be accelerated by steroid administration or the habit of strongly rubbing the eyelid, but this may not be the original cause of cataract formation. (3) Two types of cataract are seen in patients with AD: (a) anterior subcapsular plaque formation and (b) anterior and posterior subcapsular opacity formation. The latter type, however, is also accompanied by epithelial damage from the early stage. (4) Significant numbers of patients with AD who have not yet shown manifest lens changes were found among the subjects.     

The effect of surfactants on the interfacial rates of reaction of CO2 and CO with liquid iron oxide

The ¹⁴CO₂-CO isotope exchange technique has been used to measure the rates of dissociation of CO₂ on liquid iron oxide containing the surface active components P₂O₅ or Na₂O, principally at 1673 K. The apparent first-order rate constant is found to decrease monotonically with small additions of P₂O₅ up to a factor of about 4 at 3.5 mol pct. Vaporization losses prevented detailed studies of the effect of Na₂O, but it is shown that there is probably a twofold increase in the rate constant at a concentration of about 0.2 wt pct and a fivefold increase at a concentration between 0.5 and 1.6 wt pct. A smoothed surface potential model, based upon the Vol’kenshtein model for catalysis by semiconductors, is developed, and it is shown that the required surface potential changes due to the segregation of P₂O₅ and Na₂O are physically reasonable.     

Effect of intrathecally administered local anesthetics on protein phosphorylation in the spinal cord

To elucidate the biochemical mechanisms of spinal anesthesia, we studied the effects of procaine and tetracaine on protein phosphorylation in the mouse spinal cord. Mice were injected intrathecally with either procaine, tetracaine (67 mM/approximately 2%, 10 microL, N = 5/drug), or saline (N = 4/group). Five minutes after injection, animals were killed with a guillotine, and the spinal cord was removed. The caudal 3-cm cord segment was homogenized and centrifuged, and an aliquot of the supernatant was used for phosphorylation assays. Calcium-dependent phosphorylation was initiated by incubating the samples in buffer containing [gamma-32P]ATP at 37 degrees for 30 min. The proteins were electrophoresed using slab gel and two-dimensional electrophoresis, and phosphorylated proteins were visualized by autoradiography. The data demonstrated that spinal anesthesia changes the phosphorylation state of five endogenous substrate proteins with apparent molecular masses of 130 (protein-a), 105 (protein-b), 55 (protein-c), 47 (protein-d), and 33 (protein-e) kDa. In two-dimensional electrophoresis, protein-a resolved into two proteins (a1 and a2). Analysis of variance of the densitometric data suggested a significant effect for the treatment (F(2,16) 735, P < 0.00005). Post hoc comparisons with the saline-treated controls, using the Newman-Keuls test, indicated that local anesthetics significantly affected phosphoproteins (P < 0.05) except for protein-al in the tetracaine-treated group. Further characterization of these phosphoproteins should aid in determining their role in the signal transduction cascade affected by spinal anesthesia.     

CO/CO2 potentiometric titrations of carbon monoxide dehydrogenase from Clostridium thermoaceticum and the effect of CO2

Acetogenic carbon monoxide dehydrogenases catalyze the reversible oxidation of CO to CO2 and the synthesis of acetyl-coenzyme A, utilizing two novel Ni-Fe-S active sites (the C- and A-clusters, respectively) and an [Fe4S4]2+/1+ cluster (the B-cluster) that serves to transfer electrons. Enzyme samples were titrated under equilibrium conditions using various partial pressures of CO in Ar and CO2 atmospheres. EPR signal intensities from each cluster were analyzed as a function of potential using the Nernst equation. The presence of CO2 raised the reduction potentials of the A-, B-, and C-clusters, and it appeared to increase the strength of CO (substrate for acetyl-CoA synthesis) binding to the reduced A-cluster. Carbon dioxide also appeared to stabilize an intermediate EPR-silent state of the C-cluster and alter the saturation/relaxation properties of the reduced B-cluster. Simulations assuming n values (number of e- involved in reduction) larger than appropriate for the individual reactions generally fit better to the titration data than those which assumed the appropriate n, indicating positive redox cooperativity. Carbon dioxide did not inhibit 1,10-phenanthroline from removing the labile Ni from the A-cluster, but it did inhibit the CO/acetyl-coenzyme A exchange activity, probably by causing CO to bind more tightly to the A-cluster. Taken together, these results indicate a significant CO2-dependent conformational change affecting the properties of all three clusters and both subunits. Since the enzyme operates in vivo in a CO2 environment, the CO2-induced conformation may be mechanistically important.     

The value of capnography and exhaled CO2 in neonatal intensive care units]

Congenital deficiency of the fibula is sometimes accompanied by femoral hypoplasia, genu valgum, patellar a/hypoplasia or dislocation, tibial bowing, foot deformity, and toe deficiency in the affected limb. 'Iliac horns' are bony projections extending posterolaterally from the ilium and considered to be pathognomonic of nail-patella syndrome. We report a 5-year-old Japanese girl with congenital complete deficiency of the left fibula, ipsilateral iliac horn and absence of the left kidney.     

The thermal decomposition of Mn2O3 and the reduction of Mn3O4 by C and CO

The thermal decomposition of Mn₂O₃ was studied at 1000°. The rate of decomposition was inherently fast and dependent on the mass-transfer characteristics of the geometry used. The rate of reduction of Mn₃O₄ by CO, coconut charcoal, coke, and pure graphite was investigated in the temperature range 900 to 1200°. It was found that the rate of reduction in CO was fast and that the overall rate of reduction by carbon was determined by the oxidation of the carbon by CO₂. In general the rate was higher for higher tempera tures and for smaller particle sizes of the oxide and the carbon. Gases such as He, Ar, or N₂ were found to decrease the rate because of the dilution effect due to back diffusion into the interparticle pores of the oxide-carbon mixture. It was further found that the oxidation of carbon by CO₂ was catalyzed by Mn₃O₄. This effect was particularly pronounced when the reductant was either graphite or coke.     

The effect of autografting on the myosin composition in skeletal muscle fibers

The purpose of the study was to investigate the changes in myosin heavy chain (MHC) and myosin light chain (MLC) isoforms following autotransplantation of extensor digitorum longus muscles. Muscles were grafted in "standard" and "nerve-intact" conditions. MHC and MLC isoforms were analyzed by sodium dodecyl sulphate gel electrophoresis. Changes in MHC isoforms 10, 30, and 60 days after grafting were similar in the "standard" and the "nerve-intact" grafts. In contrast to MHC, changes in MLC were different in the 10th day groups, but the same in the 30th day groups. Sixty days after grafting the content of MLC isoforms was the same as the control muscles. These data indicate that transient loss of functional innervation, even for a short time, has permanent effect on the composition of MHC but not MLC isoforms in regenerating skeletal muscle fibers.     

Promotional effect of CO pretreatment on CuO/CeO2 catalyst for catalytic reduction of NO by CO

The CuO/CeO2 catalysts were investigated by means of X-ray diffraction(XRD),laser Raman spectroscopy(LRS),X-ray photoelectronic spectroscopy(XPS),temperature-programmed reduction(TPR),in situ Fourier transform infrared spectroscopy(FTIR) and NO+CO reaction.The results revealed that the low temperature(150 °C) catalytic performances were enhanced for CO pretreated samples.During CO pretreatment,the surface Cu+/Cu0 and oxygen vacancies on ceria surface were present.The low valence copper species activated the adsorbed CO and surface oxygen vacancies facilitated the NO dissociation.These effects in turn led to higher activities of CuO/CeO2 for NO reduction.The current study provided helpful understandings of active sites and reaction mechanism in NO+CO reaction.     

Kinetics of oxidation of carbonaceous materials by CO2 and H2O between 1300 °C and 1500 °C

The kinetics of the oxidation of graphite, metallurgical coke, and glassy carbon by CO₂ and H₂O were investigated at temperatures between 1300 °C and 1500 °C. The experimental technique employed a lance-crucible geometry with continuous gas analysis to measure the reaction rate. The experiments were designed to ensure that the carbon reaction behavior was in the limited mixed regime, where only a small volume of material close to the surface is reacting, and external gas phase mass transfer was fast. The results demonstrated the importance of internal pore structure, particularly as it develops in the reacted layer during the course of the reaction. This was believed to be responsible for the higher rates measured in graphite than in coke and the time-dependent rate increase that was observed in nonporous glassy carbon during experiments. For a commercial grade graphite and metallurgical coke, the rate constants depended strongly upon the carrier gas species, indicating that molecular diffusion was the primary transport mechanism in the pores of these materials. In contrast, for a specially purified graphite, the rate constant was found to be independent of the carrier gas species, which suggested Knudsen diffusion control dominates in this carbon. The results are in good agreement with extrapolations of previous work carried out at lower temperatures.