Motor unit power spectrum and firing rate

Changes in the power density spectrum of myoelectric signal with contraction level have been reported in the literature. These changes can be induced by a number of possible factors including recruitment of differing types of units, conduction velocity changes and firing rate changes. In the paper the single unit power spectrum is investigated and the effects of firing rate mean and variance changes evaluated. Motor unit signal simulation and experiments are carried out to verify predictions. The results show that spectrum peaks will shift with firing rate and the median frequency is weakly dependent on firing rate.

Heterogeneity of fast-oxidative muscle fibers of chicken demonstrated by anti-myosin monoclonal antibodies

The fiber type composition of two fast muscles of the chicken, namely, adductor superficialis (AS) and pectoralis major (PM) was examined by the histochemical myosin ATPase staining and immunochemical techniques using monoclonal antibodies (McAbs). Two new McAbs produced against the myosin of the anterior latissimus dorsi (ALD) muscle of the chicken and named ALD-122 and ALD-83 were characterized to be specific for myosin heavy chain (MHC) and for myosin light chain-1 respectively. They were used in conjunction with previously reported McAbs specific for slow MHC (ALD-47), fast MHC (MF-14) and fast light chain-2 (MF-5). By the histochemical ATPase test most muscle fibers of AS and PM muscles reacted as IIA and IIB respectively. By immunofluorescent staining with the anti-MHC McAbs, ALD-122 and MF-14, the fibers of AS muscle showed remarkable heterogeneity whereas PM muscle fibers reacted uniformly. Differences in the myosin light chain composition of AS and PM muscles were also found by SDS-gel electrophoresis and immunoblot analysis with the anti-light chain McAb, ALD-83. The study clearly indicated that the histochemically homogenous (type IIA) AS muscle is composed of several subpopulations of fibers which differ in their myosin composition and that this heterogeneity of the muscle is not simply due to presence of variable amounts of slow myosin in its fibers.

Antimalarial properties of ebselen

The seleno-organic compound ebselen showed anti-malarial activity in vitro against the murine Plasmodium berghei and the human P. falciparum. In P. berghei, the uptake and incorporation of [3H]-methionine and [3H]-adenosine was inhibited and the infectivity of plasmodia was reduced. Ebselen affects the development of asexual stages of chloroquine-resistant and -sensitive P. falciparum strains. Its IC50 for P. falciparum was about 14 mumol/l and that for P. berghei, about 10 mumol/l. The growth of P. falciparum was blocked by ebselen at all stages, including the invasion of erythrocytes by merozoites. In a human hepatoma cell line and in mouse peritoneal macrophages, no cytostatic or cytotoxic effects were found, indicating selective inhibition of plasmodia by ebselen. Its in vitro inhibitory effect is discussed in relation to its possible reactivity with thiol groups and its lack of an anti-malarial effect in infected mice.

Determination of Settings of a Tilted Head Cutter for Generation of Hypoid and Spiral Bevel Gears

Kinematics of mechanisms of hypoid and spiral bevel cutting machines is considered. These mechanisms are designated to install the position and tilt of the head cutter. The tilt of the head cutter with standard blades provides the required pressure angle. The authors have developed the matrix presentation of kinematics of these mechanisms and basic equations for the required settings. An example is presented based on the developed computation procedure.

Mitochondria contain a proteolytic system which can recognize and degrade oxidatively-denatured proteins

When incubated with mitochondria in an air atmosphere, menadione and doxorubicin (which redox cycle with the respiratory chain to produce oxygen radicals), as well as xanthine oxidase plus xanthine (which generate superoxide and H2O2), stimulated the degradation of newly-synthesized [( 3H]leucine-labelled) mitochondrial polypeptides. No stimulation was observed in an N2 atmosphere, ATP was not required, and xanthine oxidase was not effective without xanthine. Various forms of oxidative stress induced varying degrees of protein cross-linking, protein fragmentation and proteolysis, as judged by gel electrophoresis and amino acid analysis. To learn more about the proteolytic enzymes involved in degradation, we undertook studies with purified protein substrates which had been exposed to oxidative stress (OH or H2O2) in vitro. Despite mitochondrial contamination with acid proteases of lysosomal (and other) origin, pH profiles revealed distinct proteolytic activities at both pH 4 and pH 8. The pH 8 activity preferentially degraded the oxidatively-denatured forms of haemoglobin, albumin and superoxide dismutase; was unaffected by digitonin; and exhibited a several-fold increase in activity upon mitochondrial disruption (highest activity being found in the matrix). In contrast, the pH 4 activity was dramatically decreased by digitonin treatment (to reduce lysosomal contamination); was unaffected by mitochondrial disruption; and showed no preference for oxidatively-denatured proteins. The pH 8 activity was not stimulated by ATP, but was inhibited by EDTA, haemin and phenylmethylsulphonyl fluoride. In contrast, the contaminating pH 4 activity was only inhibited by pepstatin and leupeptin. Thus, our experiments reveal a distinct mitochondrial (matrix) proteolytic pathway which can preferentially degrade oxidatively-denatured proteins.

Synthesis of interleukin 6 (interferon-beta 2/B cell stimulatory factor 2) in human fibroblasts is triggered by an increase in intracellular cyclic AMP

Interleukin 6 (IL-6; also referred to as interferon-beta 2, 26-kDa protein, and B cell stimulatory factor 2) is a cytokine whose actions include a stimulation of immunoglobulin synthesis, enhancement of B cell growth, and modulation of acute phase protein synthesis by hepatocytes. Synthesis of IL-6 is stimulated by interleukin 1 (IL-1), tumor necrosis factor (TNF), or platelet-derived growth factor. We examined the role of the cyclic AMP (cAMP)-dependent signal transduction pathway in IL-6 gene expression. Several activators of adenylate cyclase, including prostaglandin E1, forskolin, and cholera toxin, as well as the phosphodiesterase inhibitor isobutylmethylxanthine and the cAMP analog dibutyryl cAMP, shared the ability to cause a dramatic and sustained increase in IL-6 mRNA levels in human FS-4 fibroblasts. Actinomycin D treatment abolished this enhancement. Treatments that increased intracellular cAMP also stimulated the secretion of the IL-6 protein in a biologically active form. Increased intracellular cAMP appears to enhance IL-6 gene expression by a protein kinase C-independent mechanism because down-regulation of protein kinase C by a chronic exposure of cells to a high dose of 12-O-tetradecanoylphorbol 13-acetate did not abolish the enhancement of IL-6 expression by treatments that increase cAMP. IL-1 and TNF too increased IL-6 mRNA levels by a protein kinase C-independent mechanism. Our results suggest a role for the cAMP-dependent pathway(s) in IL-6 gene activation by TNF and IL-1.

T cell epitopes in experimental autoimmune myasthenia gravis of the rat: strain-specific epitopes and cross-reaction between two distinct segments of the alpha chain of the nicotinic acetylcholine receptor (Torpedo californica)

T cell epitopes on the nicotinic acetylcholine receptor (A ChR) of Torpedo californica were analyzed using T cell lines isolated from Lewis, BN, and (Lewis X BN)F1 rats. All lines selected for reactivity against either native or denatured AChR or for 6 selected synthetic peptides of the AChR alpha chain expressed the CD4 membrane phenotype and recognized their antigen in the context of major histocompatibility complex class II determinants. They were tested in vitro for reactivity with each of these antigens. The results indicate that parental Lewis and BN rat T lymphocytes recognize distinct molecular epitopes on the AChR protein, whereas (Lewis X BN)F1 hybrids respond against both sets of epitopes. Two peptides (P10 and P11) which represent distinct amino acid sequences on the putatively extracellular part of the AChR alpha chain, and which share only 4 common amino acids, two of them contiguous, showed an unexpected cross-reactivity in the Lewis rat. T cells selected for either peptide co-recognize the other peptide in vitro. In addition, these cells are responsive against full length AChR. P11, in particular, appears to be a major epitope for Lewis rats immunized with AChR.

Glutathione reductase-deficient erythrocytes as host cells of malarial parasites

BCNU [1,3-bis(2-chloroethyl)-1-nitrosourea] and its less toxic derivative HeCNU [1-(2-chloroethyl)-3-(2-hydroxyethyl)-1-nitrosourea] are clinically-used antitumour drugs. In erythrocytes BCNU is a highly specific inhibitor of the enzyme glutathione reductase [H. Frischer and T. Ahmad, J. Lab. clin. Med. 89, 1080 (1977)]. When treating erythrocytes in vitro, 50% enzyme inhibition was obtained with 1 microM BCNU or 3 microM HeCNU within 2 hr. The two drugs were used for preparing red cell populations with various levels of glutathione reductase activity; complete inhibition (greater than or equal to 98%) was only achieved when the medium contained glucose as a source of reducing equivalents. The erythrocytes were then tested in drug-free media as host cells for the malaria parasite Plasmodium falciparum. In the range of 0-300 mU/ml cells, there was a correlation between glutathione reductase activity and parasite growth; erythrocytes with an activity of less than 20 mU/ml did not serve as host cells for P. falciparum at all although these erythrocytes were viable. When the culture medium was supplemented with 20 mM glutathione (GSH), parasite growth was normal irrespective of the glutathione reductase level in the erythrocytes. This is consistent with the finding that poisoning glutathione reductase led to a 10-fold decrease of the cytosolic GSH level. Our results corroborate the concept that intraerythrocytic inhibition of glutathione reductase mimicks the biochemistry of drug-sensitive glucose-6-phosphate dehydrogenase deficiency (favism), an inherited condition which confers protection from malaria.

Site-directed mutagenesis of a residue located in the regulatory site of Escherichia coli aspartate transcarbamoylase. Involvement of lysine 94 in effector binding and the allosteric mechanism

Lysine 94 in the regulatory chain of aspartate transcarbamoylase has been changed to a glutamine residue by site-directed mutagenesis. The resulting enzyme is almost insensitive to the activator ATP and shows a substantially reduced response to the feedback inhibitor CTP. Competition experiments indicate that ATP is still able to bind at low concentrations to the regulatory site of the mutant enzyme, even though no stimulation could be detected. When the nucleosides adenosine or cytidine were used, the saturation curves of the mutant and the wild-type enzyme became indistinguishable. Together these results indicate that lysine 94 is strongly involved in the binding of ATP and CTP by interacting specifically with the triphosphate moiety of these nucleotide effectors. Furthermore, unlike the wild-type enzyme, the inhibitory and stimulatory effects in the mutant enzyme are insensitive to changes in aspartate concentrations, implying that the lysine 94 side chain is also involved in the allosteric mechanism of the enzyme.

X-ray Line Broadening Study on Shock-modified Zirconia

Zirconia (Zr02) powder compacts have been subjected to controlled, quantitative high pressure shock loading at peak pressures from 5-27 GPa and preserved for post-shock analysis. The overlapping broadened X-ray diffraction peak profiles have been separated by least-squares fitting procedures. The separate lines have been analysed in the usual manner to determine the residual lattice strain and the coherent crystallite sizes. Maximum modification effects are observed near 20 GPa with strain values near 3 x 10-3 and size values near 200 A.

Mapping of human fibronectin receptor beta subunit gene to chromosome 10

Human-mouse hybrid cells were examined by indirect immunofluorescence with Mab DH12, a monoclonal antibody that recognizes the beta subunit of the human fibronectin receptor. Cells that expressed the antigen at their surface were sorted by FACS and karyotyped. Immunoaffinity chromatography on Mab DH12 was used to confirm the presence of the human antigen. The chromosome assignment was strengthened by isozyme analysis of markers for chromosomes 9 and 10. The results are suggestive for a 10p mapping of this beta subunit of the fibronectin receptor. Since the gene coding for the beta subunit of the VLA proteins was previously assigned to the same chromosome, our result could provide further evidence for the relationship between the beta subunit of the human fibronectin receptor and the VLA protein family.

Inhibition of hemoglobin degradation in Plasmodium falciparum by chloroquine and ammonium chloride

The effect of chloroquine (CQ) and NH4Cl on hemoglobin degradation within Plasmodium falciparum was studied by SDS gel electrophoresis. CQ inhibited hemoglobin digestion such that accumulation of hemoglobin in the parasites occurred. Quantitative analysis indicated that the content of hemoglobin in isolated CQ-treated parasites was increased from 2.39 +/- 0.47 micrograms hemoglobin (Hb)/mg protein to 8.34 +/- 0.77 micrograms Hb/mg protein (P less than 0.001) within 45 min and further to 18.7 +/- 1.23 micrograms Hb/mg protein for 2 hr compared with the untreated parasites. These results suggest that the inhibition of hemoglobin degradation in malarial parasites might be the primary target of CQ antimalarial action. The CQ-like effect on the hemoglobin digestion in P. falciparum was observed with another lysosomotropic weak base, NH4Cl, suggesting that the CQ effect on hemoglobin degradation and its antimalarial action, as well as the effect of NH4Cl, are related to their properties of lysosomotropic weak base.

Electrolyte transport in a central core model of the renal medulla

Transport of Na+, K+, Cl-, urea, and water is described in a central core model of the renal medulla. Equations for mass balance, Poiseuille flow, and the Nernst-Planck equation describe the continuous behavior of the system along the medullary axis and along the distal nephron; the Kedem and Katchalsky phenomenology describes passive transmural transport; active transmural transport obeys Michaelis-Menten kinetics. Numerical solution of the differential equations shows that to a close approximation any combination of active Na+ and active Cl- transport can generate the same concentration profiles but will generate very different potential profiles, and consequently, very different K+ absorption in thick ascending limb of Henle's loop. If a net transport stoichiometry of 2 Cl- ions to 1 Na+ ion is selected for the pumps, an active Cl- transport rate of approximately 10,000 peq.s-1.cm-2 gives K+ and Na+ concentrations in early distal nephron and a medullary osmolality profile in reasonable agreement with experimental data.

Effects of some alcohols on the conformation of mitochondrial H+-ATPase complex and F1-ATPase from pig heart

The conformations of the H+-ATPase complex and F1-ATPase in low concentrations of methanol, ethanol, n-propanol, iso-propanol and t-butanol were studied by circular dichroism. For F1-ATPase, all but methanol first increased and then decreased the circular dichroism magnitude of helical bands as the alcohol concentration was increased. With ethanol, n-propanol, iso-propanol and t-butanol, the alpha-helix content reached a maximum at about 5% alcohol and began to decrease at 10%. The content of beta-sheet showed the opposite effect, reaching a minimum at 5% and increasing slightly at higher concentrations. None of the alcohols studied had a significant effect on the conformation of the H+-ATPase complex. This difference implies that the alcohols had a greater effect on free F1-ATPase than on the membrane-bound F1-ATPase. The hydrophobic protein F0 and the membrane lipids in the H+-ATPase complex may stabilize and protect F1 from the effects of the alcohols.

Quantification of mitral regurgitation by Doppler echocardiography

The present study was undertaken to evaluate a new non-invasive approach to the quantification of mitral regurgitation. Doppler echocardiography and left ventriculography were performed in 20 patients without valvular heart disease (group A), and in 30 patients with pure mitral regurgitation (group B). Volumetric flows through the aortic and mitral valve orifices were determined by Doppler technique. The aortic flow (AF) was calculated as the product of the aortic orifice area by the systolic velocity integral. The mitral flow (MF) was computed as the product of the corrected mitral orifice area by the diastolic velocity integral. The mitral regurgitant fraction (RF) was calculated as: RF = 1 - AF/MF. In group A, there was a close agreement between aortic and mitral flows (r = 0.94, P less than 0.001), and there was no significant difference between the two measurements. In group B, the mitral flow was significantly higher than the aortic flow. The regurgitant fraction assessed by Doppler echocardiography correlated well with the grades of severity of regurgitation obtained at left ventriculography. We conclude that combined measurement of both aortic and mitral flows by Doppler echocardiography provides a new and promising approach to the noninvasive quantification of mitral regurgitation.

An immunocytochemical study of type I muscle fibres in developing human skeletal muscles

An immunocytochemical study was done on the skeletal muscles of human fetuses (19-36 weeks gestation), infants and adults using a new monoclonal antibody (McAb) ALD-47. The antibody was generated against slow myosin of chicken and is specific for myosin heavy chain (MHC). In human infants and adults the type I muscle fibres are strongly reactive with this McAb and the type II fibres uniformly non-reactive. In the fetuses from 19-20 weeks gestation (in whom the fibre types are not distinguishable by the histochemical myosin ATPase test) a proportion of muscle fibres react specifically with ALD-47. Other muscle fibres at this stage react positively with a fast specific MHC McAb HM-1.2 or are negative to both ALD-47 and HM-1.2 antibodies. These McAbs, thus, identify three distinct fibre populations in the early fetal muscle which by histochemical staining appears homogeneous. The percentage of ALD-47 positive fibres increases in fetuses at later gestational periods; at all stages these fibres lack reactivity with the HM-1.2 antibody. Because of its selective fibre type reactivity in differentiating muscles, the McAb ALD-47 in conjunction with HM-1.2 should be useful in immunoaffinity fractionation and biochemical studies of myosin isoforms in developing human muscles.

Species characteristics of the hepatic xenobiotic and steroid biotransformation systems of two teleost fish, Atlantic cod (Gadus morhua) and rainbow trout (Salmo gairdneri)

Groups of Atlantic cod and rainbow trout were treated (ip) with beta-naphthoflavone (BNF), phenobarbital, or peanut oil (controls), and properties of the hepatic xenobiotic and steroid metabolizing enzyme systems were evaluated. In both species, BNF treatment resulted in significant induction of microsomal 7-ethoxycoumarin O-deethylase, 7-ethoxyresorufin O-deethylase, biphenyl 4-hydroxylase, and phenanthrene oxidation, especially at the 1,2-position. Immunochemical studies with rabbit IgG prepared against the major BNF-inducible cytochrome P-450 in cod, P-450c, revealed increased amounts of immunoreactive protein in liver slices from both species after BNF treatment. The molecular weight of the induced protein was approximately 58,000 Da, as shown by Western blotting. When titrating biphenyl 4-hydroxylation, however, the antibodies distinguished between the two species, inhibiting the activity of BNF-induced cod 90% and that of rainbow trout 40% at 10 mg IgG/nmol P-450. Furthermore, cytochrome b5 content and UDP-glucuronyltransferase activity were significantly induced only in rainbow trout, whereas the specific content of cytochrome P-450 was significantly increased only in cod. Differences between the two species were observed in the levels of constitutive activities, the amount of induction, and in the regioselectivity of phenanthrene oxidation and androstenedione metabolism. Treatment with phenobarbital showed no effect on any of the parameters investigated in either species. The results show that although there are many common features of the hepatic xenobiotic and steroid biotransformation systems of the two teleosts, certain species characteristics exist in constitutive properties and induction responses.

Malaria: an intra-erythrocytic neoplasm?

Drug resistance is a serious problem in malaria, and prospects for new drugs are not optimistic. In 1963, the US Army began a huge programme to develop new antimalarials; they screened over 235 000 compounds, but very few were sufficiently active and safe for use in humans. Part of the problem is that not enough is known about the biochemical properties of malaria parasites, especially the metabolic differences between them and their host cells which could offer targets for specific chemotherapy. An important characteristic of malaria infection is the rapid growth of the parasite population, and changes in host metabolism that result from this. A similar effect occurs in many cancers. In this article, Ya Zhang argues that malaria parasites also have metabolic similarities with tumour cells, and suggests that careful comparison of these two could provide insight for new drug development.

A simple and rapid solid-phase RNA sequencing method

A simple and rapid solid-phase RNA sequencing method has been developed based on Peattie's direct chemical method. 3'-Terminally labeled RNA was immobilized on DEAE-cellulose sheets and followed by specific modification with dimethyl sulfate, diethylpyrocarbonate, hydroxylamine (at pH 10 for the uridine and pH 5.5 for the cytidine reaction), and cleavage reaction with aniline. RNA fragments were washed from the DEAE-cellulose sheets using salt solutions, precipitated with ethanol, and separated by 15% polyacrylamide gel electrophoresis. Due to the complete removal of the impurities normally present in the solution method, the higher resolution of the sequencing bands and lower background on the autoradiograph make this solid-phase technique more efficient. This solid-phase technique is much faster and more convenient than the original method.

On the mechanism of the reconstitution of F1-depleted ATPase complex with purified F1: possible conformational effects

The membrane sector (F0) of H+-ATPase was prepared by trypsin and urea treatment of F1-F0 and reconstituted with purified F1. The oligomycin sensitivity of the reconstituted F1-F0 complex obtained by treating F1 or F0 with Mg2+ before binding is much higher than that obtained without Mg2+ treatment. The greater change in the intrinsic fluorescence of the reconstituted F1-F0 complex obtained by Mg2+ treatment suggests that conformational changes may occur during the reconstitution. We deduce that Mg2+ binds to membrane lipids, thus decreasing membrane fluidity and changing the physical state of the lipids to provide a suitable microenvironment for conformational changes in F0. The data also suggest that the conformational change in the F0 portion of the F1-F0 complex can be transmitted to the F1 portion, the conformation of which is in turn altered, resulting in the formation of an F1-F0 complex with high oligomycin sensitivity. On the other hand, Mg2+ may act on F1 directly to induce a suitable conformational change which is then transmitted to F0, resulting in the formation of an H+-ATPase with greater sensitivity to oligomycin.

Lysis of malarial parasites and erythrocytes by ferriprotoporphyrin IX-chloroquine and the inhibition of this effect by proteins

Ferriprotoporphyrin IX(FP) lysed both erythrocytes and isolated Plasmodium falciparum as judged by decrease in turbidity of erythrocyte and parasite suspensions. The lytic effect of FP on erythrocytes was enhanced by chloroquine (CQ). In the presence of 2.5-20 microM CQ, 5 microM FP led to complete hemolysis within 45 min. However, the lytic effect of FP or FP-CQ on both erythrocytes and parasites was inhibited completely by proteins. The protein inhibition was non-specific. This finding, the failure of FP and FP--CQ to cause hemolysis and lysis of malarial parasites in a protein-containing medium, does not support the "FP--CQ complex hypothesis" for the antimalarial action of chloroquine.

Stage-dependent inhibition of chloroquine on Plasmodium falciparum in vitro

Morphological observation of the life cycle of the malaria parasite, Plasmodium falciparum, in highly synchronous cultures after an exposure to therapeutic concentrations of chloroquine in ring, trophozoite and schizont stages, respectively, were carried out in order to determine the influence of chloroquine on the growth of the different stages of the malarial parasites. It was found that chloroquine could not affect merozoite invasion of the erythrocytes; the ring stage was more sensitive to chloroquine than the trophozoite and schizont stages; and chloroquine in therapeutic concentrations prevented only the transformation of rings to trophozoites and could not affect the transformations of trophozoites to schizonts and schizonts to new rings. The determination of the IC50 of chloroquine showed that the IC50 of trophozoites was about 6 times as high as that of rings.

Analysis of methodology for quantifying mitral regurgitation by Doppler echocardiography

It is generally agreed that Doppler echocardiography is highly sensitive and specific for the detection of mitral regurgitation. There is more confusion about its ability to quantitate the degree of mitral regurgitation. Studies of the intensity of the Doppler signals, as well as cross sectional Doppler studies apparently can provide a straightforward, but rough estimate of the degree of regurgitation in term of atrial extent of the disturbed flow. The methods are also sensitive to methodological errors as beam direction, movement of the heart, signal/noise relationship and the size of the left atrium. Another approach to the non-invasive measurement of mitral regurgitation includes the use of Doppler echocardiography for the determination of both aortic and mitral volumetric flow. In a study of patients with mitral regurgitation, we found a close correlation between the regurgitant fraction determined by Doppler echocardiography, and the regurgitant severity determined by left ventriculography. This technique can only be used in pure mitral regurgitation, while associated atrial fibrillation, mitral stenosis, and combined aortic and mitral regurgitation make correct measurements difficult.