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PubMed1994

Kinetics of CO binding to cytochromes P450 in the endoplasmic reticulum.

The kinetics of CO binding to cytochromes P450 in rat liver microsomes were examined using the flash photolysis technique. Modulation of the kinetics by P450 form-specific effectors such as anti-P450 monoclonal antibodies and substrates was used to elucidate the kinetic behavior of individual P450s within the endoplasmic reticulum. The problem of attributing a kinetic parameter to a single P450 in the presence of multiple microsomal P450s was overcome with a difference method that employs the difference of the kinetic profiles obtained in the presence and absence of a P450 effector. Applying this approach to study the conformation/dynamics of P450 2B1 in microsomes from phenobarbital-treated rats revealed that the substrate benzphetamine enhances while testosterone inhibits the rate of CO binding to this P450. Similar experiments with P450 1A1 in microsomes from 3-methylcholanthrene-treated rats showed that the substrate benzo[a]pyrene accelerates CO binding. These results show that the access channel between solvent and heme in the P450 interior can be altered in a substrate- and P450-dependent manner to either hinder or facilitate CO diffusion to the heme iron. These results also demonstrate that analytical difference methods may be employed to characterize the conformation of individual P450s in their native membrane environment in the endoplasmic reticulum.

Animals↗
PubMed1983

Unique cytochalasin B binding characteristics of the hepatic glucose carrier.

Cytochalasin B is shown to inhibit uptake of 3-O-methylglucose into isolated rat hepatocytes with a Ki = 1.9 microM. The nature of this inhibition was characterized by studies of [3H]cytochalasin B binding to liver plasma membranes. Scatchard analysis of [3H]cytochalasin B binding reveals a complex curvilinear binding pattern. This pattern can be resolved into three components: (1) a high-affinity (ca. 10(-8) M) cytochalasin E sensitive site unrelated to glucose uptake, (2) a glucose-sensitive site, and (3) a low-affinity site. When 5 microM cytochalasin E is employed to mask the high-affinity site, glucose displaces 40-60% of the remaining [3H]cytochalasin B binding. Analysis of this glucose-sensitive cytochalasin B binding according to Scatchard reveals a Kd = 1.7 microM, indistinguishable from the concentration of cytochalasin B which half-maximally inhibits hepatic glucose uptake. These data identify a glucose-sensitive cytochalasin B binding site in liver plasma membranes which corresponds to the glucose carrier in the intact hepatocyte. The Ki of 1.9 microM for inhibition of hepatic glucose uptake by cytochalasin B and the Kd of 1.7 microM for [3H]cytochalasin B binding to liver plasma membranes are values 1 order of magnitude higher than values for the same parameters determined in all previous studies of facilitated hexose diffusion systems. The hepatic hexose carrier is therefore unique, and this uniqueness may be of regulatory significance with regard to glucose homeostasis.

Animals↗
PubMed1986

Anomalous driving force for renal brush border H+/OH-transport characterized by using 6-carboxyfluorescein.

The pH, delta pH, and membrane potential dependences of H+/OH-permeability in renal brush border membrane vesicles (BBMV) were studied by using the entrapped pH indicator 6-carboxyfluorescein (6CF). Quantitative H+/OH-fluxes (JH) were obtained from a calibration of the fluorescence response of 6CF to intravesicular pH using vesicles prepared with varying intravesicular and solution pHs. Intravesicular buffer capacity, determined by titration of lysed vesicles, increased monotonically from 140 to 260 mequiv/L in the pH range 5-8. JH was measured by subjecting voltage-clamped BBMV (K+/valinomycin) to preformed pH gradients over the pH range 5-8 and measuring the rate of change of intravesicular pH. For small preformed pH gradients (0.4 pH unit) JH [6 nequiv s-1 (mg of protein)-1] was nearly independent of pH (5-8), predicting a highly pH dependent H+ permeability coefficient. JH increased in a curvilinear manner from 6 to 104 nequiv s-1 (mg of protein)-1 as delta pH increased from 0.4 to 2.5. JH increased linearly [1.6-7.3 nequiv s-1 (mg of protein)-1] with induced K+ diffusion potentials (21-83 mV) in the absence of a pH gradient. These findings cannot be explained by simple diffusion of H+ or OH- or by mobile carrier models. Two mechanisms are proposed, including a lipid diffusion mechanism, facilitated by binding of H+/OH- to fixed sites in the membrane, and a linear H2O strand model, where dissociation of H2O in the membrane fixes H+ and OH- concentrations in strands, which can result in net H+/OH- transport.

Animals↗
PubMed1989

Analysis of protein-mediated 3-O-methylglucose transport in rat erythrocytes: rejection of the alternating conformation carrier model for sugar transport.

3-O-Methylglucose (3OMG) transport in rat erythrocytes (RBCs) is mediated by a low-capacity, facilitated diffusion-type process. This study examines whether the characteristics of sugar transport in rat RBCs are consistent with the predictions of two diametric, theoretical mechanisms for sugar transport. The one-site carrier describes a transport mechanism in which sugar influx and efflux substrate binding sites are mutually exclusive. The two-site carrier describes a transport mechanism in which sugar influx and efflux substrate binding sites can exist simultaneously but may interact in a cooperative fashion when occupied by substrate. Michaelis and velocity parameters for saturable 3OMG transport in rat erythrocytes at 24 degrees C were obtained from initial rate measurements of 3OMG transport. The results are incompatible with the predictions of the one-site carrier but are consistent with the predictions of a symmetric two-site carrier, displaying negligible cooperativity between substrate binding sites. This allows reduction of the two-site carrier transport equations to a form containing fewer constants than the one-site carrier equations without limiting their predictive success. While the available evidence does not prove that rat erythrocyte sugar transport is mediated by a two-site mechanism, we conclude that adoption of the formally more complex one-site model for sugar transport in rat erythrocytes is unnecessary and unwarranted. Counterflow experiments have also been performed in which the time course of radiolabeled 3OMG uptake is measured in cells containing saturating levels of 3OMG. The results of these experiments are consistent with the hypothesis [Naftalin et al. (1985) Biochim. Biophys. Acta 820, 235-249] that exchange of sugar between intracellular compartments (cell water and hemoglobin) can be rate limiting for transport under certain conditions.

3-O-Methylglucose↗
PubMed2001

Structure-motion-performance relationship of flux-enhanced reverse osmosis (RO) membranes composed of aromatic polyamide thin films.

The present paper explores the role of dimethyl sulfoxide (DMSO) used as an additive to modify the morphological as well as the molecular nature of aromatic polyamide during the formation of thin-film-composite (TFC) membranes. In addition, it elucidates the mechanism of enhancing the reverse osmosis (RO) permeation of the resulting membranes in proportion to the addition of DMSO. Morphological studies by atomic force microscopy (AFM) observed that as the concentration of DMSO increased, the surface roughness and the surface area of the aromatic polyamide TFC membranes became higher and larger, compared to FT-30 membrane for which DMSO was not added during interfacial reaction. Such morphological changes were brought about from fluctuating interface through reducing the immiscibility between aqueous/organic phases by DMSO and provided more opportunities to have contact with water molecules on the surface, participating in the enhancement of the water permeability. Chemical composition studies by X-ray photoelectron spectroscopy (XPS) revealed that there was a considerable increase of the cross-linked amide linkages relative to the linear pendant carboxylic acid groups in the TFC membranes of more DMSO addition. The increase of such amide linkages as hydrogen bonding sites facilitated the diffusion of water molecules through the thin films and played a favorable role in elevating water flux without considerable loss of salt rejection. Relaxation and motion analyses by 1H solid-state nuclear magnetic resonance (NMR) spectroscopy also confirmed the XPS revelation on the basis of measurements of the spin-lattice relaxation time in the rotating frame, T1rho, and determination of the correlation time, tau(c), for the aromatic polyamides forming thin films. The trend of longer tau(c)'s with the increase of DMSO concentration reflected the thin-film aromatic polyamides of less locally mobile chains, accompanied by the higher degree of cross-linking and, hence, the greater number of amide groups. The combined results of AFM, XPS, and solid-state NMR provided a robust explanation for the mechanism of flux enhancement of the aromatic polyamide TFC membranes with the addition of DMSO, which would contribute to not only a fundamental understanding of the process but also an advanced designing of the so-called "tailor-fit" TFC membranes.

Dimethyl Sulfoxide↗
PubMed2006

Homoallylic alcohol isomerization in water over an immobilized Ru(II) organometallic catalyst with mesoporous structure.

PPh(2)-functionalized SBA-15 was synthesized by co-condensation of tetraethyl orthosilicate and 2-(diphenylphosphino)ethyltriethoxysilane through prehydrolysis. The as-prepared PPh(2)-SBA-15 was used as the support to immobilize the Ru(II) organometallic catalyst through the strong coordination between the Ru(II) and the PPh(2)-ligand (Ru-PPh(2)-SBA-15). During 1-phenyl-3-buten-1-ol isomerization carried out in water as an environmentally friendly medium, the Ru-PPh(2)-SBA-15 catalyst exhibited almost the same activity and selectivity as the corresponding RuCl(2)(PPh(3))(3) homogeneous catalyst and could be used repetitively nearly 7 times. On the basis of various characterizations, the correlation of the catalytic behaviors of the Ru-PPh(2)-SBA-15 to its structural characteristics was discussed briefly. Obviously, the high activity of the Ru-PPh(2)-SBA-15 could be attributed to both the high surface area of the support, which ensured the good dispersion of Ru(II) active sites, and the ordered mesoporous structure, which facilitated the diffusion of organic reactants.

Journal Article↗
PubMed2000

Functional characterization of the conserved "GLK" motif in mitochondrial porin from Neurospora crassa.

Mitochondrial porin facilitates the diffusion of small hydrophilic molecules across the mitochondrial outer membrane. Despite low sequence similarity among porins from different species, a "glycine-leucine-lysine" (GLK) motif is conserved in mitochondrial and Neisseria porins. To investigate the possible roles of these conserved residues, including their hypothesized participation in ATP binding by the protein, we replaced the lysine residue of the GLK motif of Neurospora crassa porin with glutamic acid through site-directed mutagenesis of the corresponding gene. Although the pores formed by this protein have size and gating characteristics similar to those of the wild-type protein, the channels formed by GLEporin are less anion selective than the wild-type pores. The GLEporin retains the ability to be cross linked to [alpha-(32)P]ATP, indicating that the GLK sequence is not essential for ATP binding. Furthermore, the pores formed by both GLEporin and the wild-type protein become more cation selective in the presence of ATP. Taken together, these results support structural models that place the GLK motif in a part of the ion-selective beta-barrel that is not directly involved in ATP binding.

Adenosine Triphosphate↗
PubMed1998

Nanoporous alkoxy-derived titanium oxide coating: a reactive overlayer for functionalizing titanium surface.

Effective immobilization of bioactive substances such as adhesive proteins, synthetic peptides and growth factors on metallic substrates is required for a number of medical applications. In the present work, evidence is presented to show that an alkoxy-derived nano-porous titanium oxide coating, synthesized electrochemically on titanium in methanolic electrolytes, may act as an effective interface for functionalizing a titanium surface. It is demonstrated that nanoporous oxide coatings could facilitate fast diffusion of small organic molecules within the oxide network and form strong chemical bonds with the functional groups of these molecules at room temperature. Fourier transformed-infrared spectroscopy was used to investigate the nature of the interfacial interactions between the oxide network and a range of molecules containing COOH, OH, NH2, C=O and phosphoric acid functional groups. The results indicate that the nanometre-sized oxide clusters within the coating may play an essential role in effective immobilization of organic molecules by providing numerous binding sites for chemisorption of these species. The surface-derivatized oxide coating may provide a solid phase for the subsequent attachment of a broad range of biochemically active molecules on the titanium surface.

Journal Article↗
PubMed2002

IgE-mediated anaphylaxis to Thiomucase, a mucopolyssacharidase: allergens and cross-reactivity.

BACKGROUND: Thiomucase is a mucopolysaccharidase obtained from ovine tissues mainly used to facilitate the diffusion of local anaesthetics and in the treatment of cellulitis. A patient with an anaphylaxis in relation to the intramuscular administration of Thiomucase is reported. OBJECTIVE: To investigate Thiomucase allergens and their possible relationship with dander allergens and animal albumins. MATERIAL AND METHODS: Skin prick tests (SPT) and serum-specific IgE were performed with Thiomucase and danders. Thiomucase SDS-PAGE immunoblotting was performed in order to study allergens. RAST/CAP inhibition and SDS-PAGE immunoblotting inhibition were carried out to study the cross-reactivity. RESULTS: Skin prick tests (SPT) were positive to Thiomucase, animal dander (cat, dog, sheep, other), bovine serum albumin (BSA), and echinococcus. Specific IgE was also positive to Thiomucase, animal dander (cat, dog, sheep, other), BSA and echinococcus. In the RAST-CAP inhibition assays BSA was nearly completely inhibited by Thiomucase, Thiomucase was partially inhibited by BSA and cat and Echinococcus granulosus was partially inhibited by sheep and Thiomucase. In the Thiomucase SDS-PAGE immunoblotting several proteins fixed IgE, ranging from 20 kDa to > 94 kDa, the strongest with 43 kDa. The IgE fixation to BSA, cat and sheep in the SDS-PAGE immunoblotting was completely inhibited by the preincubation of the serum with Thiomucase. CONCLUSIONS: An IgE-mediated anaphylaxis to Thiomucase is documented. Multiple allergens are recognized in Thiomucase by the patient serum, the main with 43 kDa. Partial cross-reactivity with BSA, cat dander and sheep dander is documented.

Anaphylaxis↗
PubMed2002

High incidence of autoantibodies in Taiwanese patients with oral submucous fibrosis.

BACKGROUND: Previous study has shown a high incidence of autoantibodies including antinuclear (ANA), antismooth muscle (SMA), antigastric parietal cell (GPCA), antithyroid microsomal (TMA), and antireticulin antibodies in a small group of 26 patients with oral submucous fibrosis (OSF). The reasons why some of the OSF patients have high titers of autoantibodies in serum have not been completely explained and no further study on autoantibodies in OSF patients has been done in a large group of patients. METHODS: In this study, we determined the serum levels of ANA, SMA, GPCA, and TMA in a large group of 109 male Taiwanese patients with OSF by an indirect immunofluorescence technique (for ANA, SMA, and GPCA), and by a semiquantitative microtiter particle agglutination test (for TMA). The presence of serum autoantibodies in OSF patients was further correlated with patients' oral habits and the severity of OSF measured by maximum mouth opening (MMO) and sites of involvement. RESULTS: We found that the frequencies of presence of serum ANA (23.9%), SMA (23.9%), and GPCA (14.7%) in OSF patients were significantly higher than those (9.2, 7.3, and 5.5%, respectively) in healthy control subjects (P < 0.01, P < 0.005, and P < 0.05, respectively). Although the frequency of presence of TMA (5.5%) in OSF patients was also greater than that (2.8%) in healthy control subjects, the difference was not significant (P > 0.05). The presence of serum GPCA in OSF patients was significantly associated with daily areca quid (AQ) consumption (P < 0.05). The presence of serum ANA in OSF patients associated with daily AQ consumption was of borderline statistical significance (P = 0.066). However, no significant correlations were demonstrated between the presence of serum autoantibodies in OSF patients and other variables of oral habits, MMO, and sites of involvement. CONCLUSION: In this study, all the 109 OSF patients had AQ chewing habit and 73.4% of the OSF patients swallowed the 'juice' of AQ during the chewing process. The presence of serum GPCA and ANA in OSF patients was associated with daily consumption of AQs. AQ chewing caused mucosal microtrauma, and ulcerations facilitated the diffusion of genotoxic and cytotoxic AQ ingredients into the oral and gastric tissues. Altered autoantigens released from AQ ingredients-damaged cells may induce autoantibody production. Higher frequencies of specific HLA-DR antigens in OSF patients may also help autoantibody production. Therefore, we conclude that the high incidence of autoantibodies in OSF patients may be due to AQ chewing habit, toxic AQ ingredients, and genetic susceptibility of the OSF patients.

Adolescent↗
PubMedDate not supplied

Primary sequence of a dimeric bacterial haemoglobin from Vitreoscilla.

Vitreoscilla, a filamentous bacterium in the Beggiatoa family, synthesizes a soluble haem-protein which has two identical subunits of relative molecular mass 15,775 and two b haems per molecule. It is synthesized in relatively large quantities when the organism, a strict aerobe, is grown under hypoxic conditions. It forms a relatively stable oxygenated form which is spectrally similar to oxymyoglobin (oxyHb) and oxyhaemoglobin (oxyHb). The amino acid sequence of this protein has been determined and aligned to fit the helical regions of several animal and plant globins. This alignment is consistent with its being a structural homologue of the eucaryotic haemoglobins although it diverged from the others in the N-terminal region and may lack an A-helix. It showed the maximum sequence homology (24%) with lupin leghaemoglobin (Lb). Vitreoscilla Hb is the first bacterial haemoglobin to be sequenced. It may function to enable the organism to survive in oxygen-limited environments by acting as an oxygen storage-trap or to facilitate oxygen diffusion.

Amino Acid Sequence↗
PubMed2003

A proteomic study reveals novel insights into the diversity of aquaporin forms expressed in the plasma membrane of plant roots.

Aquaporins are channel proteins that facilitate the diffusion of water across cell membranes. The genome of Arabidopsis thaliana encodes 35 full-length aquaporin homologues. Thirteen of them belong to the plasma membrane intrinsic protein (PIP) subfamily and predominantly sit at the plasma membrane (PM). In the present work we combine separations of membrane proteins (by one- and two-dimensional gel electrophoresis) with identification by MS (matrix-assisted laser-desorption ionization-time-of-flight and electrospray-ionization tandem MS) to take an inventory of aquaporin isoforms expressed in the PM of Arabidopsis thaliana roots. Our analysis provides direct evidence for the expression of five PIPs (PIP1;1, PIP1;5, PIP2;1, PIP2;2 and PIP2;7) in the root PM and suggests the presence of at least three other PIP isoforms. In addition, we show that the same PIP isoform can be present under several forms with distinct isoelectric points. More specifically, we identify phosphorylated aquaporins in the PIP1 and PIP2 subgroups and suggest the existence of other post-translational modifications. Their identification should provide clues to reveal novel molecular mechanisms for aquaporin regulation.

Amino Acid Sequence↗
PubMed1997

Adaptation of myoglobin in compensatory hypertrophied rat muscle.

This study investigated the time course change of myoglobin concentration ([Mb]) in skeletal muscle during muscle hypertrophy in rats. Seven groups of Wistar rats (n = 7 per group) were examined. Compensatory hypertrophy of the plantaris muscle was induced by the bilateral ablation of the medial and lateral heads of the gastrocnemius muscle, and the effect of compensatory hypertrophy on the [Mb] of the plantaris muscle was examined at 7, 21 and 42 days post-ablation. The [Mb] expressed as mg g(-1) wet muscle weight tended to decline at 7 days post-ablation (-12.1%) and returned to the control level by 42 days post-ablation, as did the muscle protein concentration. However, the [Mb] expressed as mg g(-1) protein weight was not significantly different between the ablation and control groups throughout the experimental period. The estimated value of absolute Mb content in the whole plantaris muscle was significantly increased by 28.4% (P < 0.01) at 42 days post-ablation compared with the age-matched controls. Therefore, the longer period of compensatory activity allowed the Mb to increase in its absolute content, although the [Mb] did not exceed the level of control muscle. The capacity of facilitated oxygen diffusion and oxygen storage by Mb in the muscle cells will not change even when muscle enlargement takes place.

Animals↗
PubMed1999

In vivo and in vitro studies of major surface loop deletion mutants of the Escherichia coli K-12 maltoporin: contribution to maltose and maltooligosaccharide transport and binding.

The trimeric protein LamB of Escherichia coli K-12 (maltoporin) specifically facilitates the diffusion of maltose and maltooligosaccharides through the outer membrane. Each monomer consists of an 18-stranded antiparallel beta-barrel with nine surface loops (L1 to L9). The effects on transport and binding of the deletion of some of the surface loops or of combinations of several of them were studied in vivo and in vitro. In vivo, single-, DeltaL4, DeltaL5, DeltaL6, and double-loop deletions, DeltaL4 + DeltaL5 and DeltaL5 + DeltaL6, abolished maltoporin functions, but not the double deletion DeltaL4 + DeltaL6 and the triple deletion DeltaL4 + DeltaL5 + DeltaL6. While deletion of the central variable portion of loop L9 (DeltaL9v) affected maltoporin function only moderately, the combination of DeltaL9v with the double deletion of loops L4 and L6 (triple deletion DeltaL4 + DeltaL6 + DeltaL9v) strongly impaired maltoporin function and resulted in sensitivity to large hydrophilic antibiotics without change in channel size as measured in vitro. In vitro, the carbohydrate-binding properties of the different loop mutants were studied in titration experiments using the asymmetric and symmetric addition of the mutant porins and of the carbohydrates to one or both sides of the lipid bilayer membranes. The deletion of loop L9v alone (LamBDeltaL9v), of two loops L4 and L6 (LamBDeltaL4 + DeltaL6), of three loops L4, L5 and L6 (LamBDeltaL4 + DeltaL5 + DeltaL6) or of L4, L6 and L9v (LamBDeltaL4 + DeltaL6 + DeltaL9v) had relatively little influence on the carbohydrate-binding properties of the mutant channels, and they had approximately similar binding properties for carbohydrate addition to both sides compared with only one side. The deletion of one of the loops L4 (LamBDeltaL4) or L6 (LamBDeltaL6) resulted in an asymmetric carbohydrate binding. The in vivo and in vitro results, together with those of the purification across the starch column, suggest that maltooligosaccharides enter the LamB channel from the cell surface side with the non-reducing end in advance. The absence of some of the loops leads to obstruction of the channel from the outside, which results in a considerable difference in the on-rate of carbohydrate binding from the extracellular side compared with that from the periplasmic side.

Bacitracin↗
PubMed2000

In vivo and in vitro studies of transmembrane beta-strand deletion, insertion or substitution mutants of the Escherichia coli K-12 maltoporin.

LamB of Escherichia coli K12, also called maltoporin, is an outer membrane protein, which specifically facilitates the diffusion of maltose and maltodextrin through the bacterial outer membrane. Each monomer is composed of an 18-stranded antiparallel beta-barrel. In the present work, on the basis of the known X-ray structure of LamB, the effects of modifications of the beta-barrel domain of maltoporin were studied in vivo and in vitro. We show that: (i) the substitution of the pair of strands beta13-beta14 of the E. coli maltoporin with the corresponding pair of strands from the functionally related maltoporin of Salmonella typhimurium yielded a protein active in vivo and in vitro; and (ii) the removal of one pair of beta-strands (deletion beta13-beta14) from the E. coli maltoporin, or its replacement by a pair of strands from the general porin OmpF of E. coli, leads to recombinant proteins that lost in vivo maltoporin activities but still kept channel formation and carbohydrate binding in vitro. We also inserted into deletion beta13-beta14 the portion of the E. coli LamB protein comprising strands beta13 to beta16. This resulted in a protein expected to have 20 beta-strands and which completely lost all LamB-specific activities in vivo and in vitro.

Amino Acid Sequence↗
PubMedDate not supplied

Factors affecting hemodialysis and peritoneal dialysis efficiency.

Hemodialysis and peritoneal dialysis are two blood purification techniques that use similar operating systems. The hemodialysis system is based on three components (blood, membrane, and dialysate). The peritoneal dialysis system is based on the same components that can, however, be less manipulated and adjusted. In hemodialysis the blood flow is the main determinant of small solute removal thanks to a prevalently diffusive mechanism. Convection is also used to transport larger solutes across the membrane, but this mechanism relies on the high permeability coefficient of the membrane and high transmembrane pressure leading to high ultrafiltration rates. The membrane can therefore influence the performance of the techniques as far as solute removal and ultrafiltration are concerned. Finally, diffusion is facilitated by an improved distribution of dialysate flow in the dialysate compartment. This can be achieved with a special dialysate pathway configuration based on space yarns or micronodulation of the fibers. In peritoneal dialysis, blood flow and membrane characteristics can be less manipulated or almost not at all. The only variables are dialysate volume, flow, dwell time, and composition. Thanks to modification in these aspects of the dialysate, peritoneal dialysis techniques with different clearances and ultrafiltration rates can be accomplished.

Efficiency↗
PubMedDate not supplied

A quantitative study on the effects of maternal smoking on placental morphology and cadmium concentration.

The aim of this study was to quantify the effects of maternal cigarette smoking on placental morphology, paying particular attention to variables known to be influential in facilitating oxygen diffusion. Structural quantities were estimated by stereological analyses of placental samples drawn from non-smoking and smoking women whose smoking habits were assessed both subjectively (from volunteered cigarette consumption) and objectively (by determining levels of plasma cotinine, a major metabolite of nicotine). Concentrations of placental cadmium were also measured. In the smoking group, maternal and fetal haematocrits were elevated and mean birthweight was reduced. Within placentae, the most significant alterations were increases in cadmium levels, the relative volumes of maternal intervillous space, the relative surface areas of fetal capillaries and decreases in the relative and absolute volumes of fetal capillaries. Findings indicate that changes in capillary volume are the result of a decrease in mean capillary diameter rather than total length. The mean thickness of the trophoblast component of the villous membrane was also increased in the smoking group. Although increased haematocrits suggest that fetuses of smoking mothers suffer hypoxic stress, these morphological changes are likely to compromise, rather than assist, transplacental oxygen transfer. This is in marked contrast to the adaptive changes seen in pregnancies associated with preplacental hypoxia and suggests that other factors might be compromising the fetoplacental unit. Finally, although the morphological changes associated with maternal smoking seem to be the result of an all-or-none, rather than dose-dependent, effect, the available evidence is not conclusive.

Cadmium↗
PubMed1997

Lactate and ammonia concentration in blood and sweat during incremental cycle ergometer exercise.

It is known that the concentrations of ammonia and lactate in blood increase during incremental exercise. Sweat also contains lactate and ammonia. The aim of the present study was to investigate the physiological response of lactate and ammonia in plasma and sweat during a stepwise incremental cycle ergometer exercise test in ten subjects. During this test lactate and ammonia were measured in blood obtained from the earlobe and in sweat collected in a bag attached to the back of the subject. At the end of each interval this bag was emptied for measuring lactate and ammonia. A disproportional increase in the concentration of lactate and ammonia in blood was found, in sweat a disproportional decrease. The lactate concentrations in sweat were higher than those in blood. We hypothesise that lactate in sweat is produced from glycogen granules of the clear cell of the eccrine gland. This lactate production results in acidification of sweat, which facilitates the diffusion of ammonia from eccrine duct cell to duct lumen. It is uncertain how far duct cell ammonia originates from plasma, the duct cell itself might produce ammonia. Part of the ammonia in sweat could come from the breakdown of urea by skin bacteria.

Adult↗