Clearance Rate Of Particles Research Articles

Cubilin Maintains Blood Levels of HDL and Albumin

Cubilin is an endocytic receptor highly expressed in renal proximal tubules, where it mediates uptake of albumin and filtered forms of apoA-I/HDL. Cubilin deficiency leads to urinary loss of albumin and apoA-I; however, the consequences of cubilin loss on the homeostasis of blood albumin and apoA-I/HDL have not been studied. Using mice heterozygous for cubilin gene deletion (cubilin HT mice), we show that cubilin haploinsufficiency leads to reduced renal proximal tubular uptake of albumin and apoA-I and significantly increased urinary loss of albumin and apoA-I. Moreover, cubilin HT mice displayed significantly decreased blood levels of albumin, apoA-I, and HDL. The levels of albumin and apoA-I protein or mRNA expressed in the liver, kidney, or intestine of cubilin HT mice did not change significantly. The clearance rate of small HDL3 particles (density>1.13 g/ml) from the blood increased significantly in cubilin HT mice. In contrast, the rate of clearance of larger HDL2 particles from the blood did not change significantly, indicating a decreased half-life for HDL particles capable of filtering through the glomerulus. On the basis of these findings, we conclude that cubilin deficiency reduces renal salvage and delivery back to the blood of albumin and apoA-I, which decreases blood levels of albumin and apoA-I/HDL. These findings raise the possibility that therapeutic increase of renal cubilin expression might reduce proteinuria and increase blood levels of albumin and HDL.

Dose-dependent pulmonary response of well-dispersed titanium dioxide nanoparticles following intratracheal instillation

In order to investigate the relationship between pulmonary inflammation and particle clearance of nanoparticles, and also their dose dependency, we performed an instillation study of well-dispersed TiO2 nanoparticles and examined the pulmonary inflammations, the particle clearance rate and histopathological changes. Wistar rats were intratracheally administered 0.1 mg (0.33 mg/kg), 0.2 mg (0.66 mg/kg), 1 mg (3.3 mg/kg), and 3 mg (10 mg/kg) of well-dispersed TiO2 nanoparticles (diameter of agglomerates: 25 nm), and the pulmonary inflammation response and the amount of TiO2 in the lung were determined from 3 days up to 12 months sequentially after the instillation. There were no increases of total cell or neutrophil counts in bronchoalveolar lavage fluid (BALF) in the 0.1 and the 0.2 mg-administered groups. On the other hand, mild infiltration of neutrophils was observed in the 1 and 3 mg-administered groups. Histopathological findings showed infiltration of neutrophils in the 1 and 3 mg-administered groups. Of special note, a granulomatous lesion including a local accumulation of TiO2 was observed in the bronchioli-alveolar space in the 3 mg-administered group. The biological half times of the TiO2 in the lung were 4.2, 4.4, 6.7, and 10.8 months in the 0.1, 0.2, 1, and 3 mg-administered groups, respectively. Neutrophil infiltration was observed as the particle clearance was delayed, suggesting that an excessive dose of TiO2 nanoparticles may induce pulmonary inflammation and clearance delay.

Temporal Variability in Phytoplankton Removal by a Commercial, Suspended Eastern Oyster Nursery and Effects on Local Plankton Dynamics

ABSTRACT Quantitative measurements of phytoplankton removal in a natural setting are needed to evaluate interactions between aquacultured bivalve populations and the surrounding environment. We report high-frequency (15-min) measurements of environmental variables relevant to oyster feeding and excretion at the inflow and outflow of an oyster nursery—floating upweller system (FLUPSY)—from June through September 2010 in the East Creek embayment, Peconic Estuary, NY. We demonstrated large variability in oyster particle clearance rate on short- (minutes to hours) to long-term (seasonal) timescales, including oyster responses to environmental variation, such as diurnal temperature and dissolved oxygen cycles, wind-driven turbulence, and the presence of harmful algae. A diel cycle in clearance rates calculated from whole FLUPSY measurements was apparent, with a maximum weight-specific clearance rate (CRW) of 2.21 L/h/g occurring around midnight, and a minimum CRW of 0.32 L/h/g at 0740 HR, coincident with the l...

PAF increases phagocytic capacity and superoxide anion production in equine alveolar macrophages and blood neutrophils

Phagocytosis exerted by alveolar macrophages and neutrophils is crucial in the clearance of exogenous particles deposited in the airways. Therefore, substances that activate these phagocytes in the airways can exert important effects on the particle clearance rate. PAF, particularly, was proved to be a potent activator of several immune cells and was shown to be present in the equine lower airways in specific conditions, such as after exercise. The present study aimed to investigate if PAF is able to increase the phagocytic capacity and the production of superoxide anion in equine alveolar macrophage and blood neutrophils. The results show that PAF increased these parameters in both phagocytes even in concentrations as low as 0.1 and 1.0nM. On that ground, the present work suggests that PAF is involved in the process of particle clearance in equine lower airways.

Multimodal silica nanoparticles are effective cancer-targeted probes in a model of human melanoma

Nanoparticle-based materials, such as drug delivery vehicles and diagnostic probes, currently under evaluation in oncology clinical trials are largely not tumor selective. To be clinically successful, the next generation of nanoparticle agents should be tumor selective, nontoxic, and exhibit favorable targeting and clearance profiles. Developing probes meeting these criteria is challenging, requiring comprehensive in vivo evaluations. Here, we describe our full characterization of an approximately 7-nm diameter multimodal silica nanoparticle, exhibiting what we believe to be a unique combination of structural, optical, and biological properties. This ultrasmall cancer-selective silica particle was recently approved for a first-in-human clinical trial. Optimized for efficient renal clearance, it concurrently achieved specific tumor targeting. Dye-encapsulating particles, surface functionalized with cyclic arginine-glycine-aspartic acid peptide ligands and radioiodine, exhibited high-affinity/avidity binding, favorable tumor-to-blood residence time ratios, and enhanced tumor-selective accumulation in αvβ3 integrin-expressing melanoma xenografts in mice. Further, the sensitive, real-time detection and imaging of lymphatic drainage patterns, particle clearance rates, nodal metastases, and differential tumor burden in a large-animal model of melanoma highlighted the distinct potential advantage of this multimodal platform for staging metastatic disease in the clinical setting.

New developments in aerosol dosimetry

Dosimetry provides information linking environmental exposures to sites of deposition, removal from these sites, and translocation of deposited materials. Dosimetry also aids in extrapolating laboratory animal and in vitro data to humans. Recent progress has shed light on: properties of particles in relation to their fates in the body; influence of age, gender, body size, and lung diseases on inhaled particle doses; particle movement to the brain via the olfactory nerves; and particle deposition hot spots in the respiratory tract. Ultrafine size has emerged as an important dosimetric characteristic. Particle count, composition, and surface properties are recognized as potentially important toxicology-related considerations. Differences in body size influence airway sizes, inhaled particle deposition, specific ventilation, and specific doses (e.g. per unit body mass). Related to body size, age, gender, species, and strain are also dosimetric considerations. Diseases, such as chronic obstructive pulmonary disease (COPD) and bronchitis, produce uneven doses within the respiratory tract. Traditional concepts of the translocation and clearance of deposited particles have been challenged. Ultrafine particles can translocate to the brain via olfactory nerves, and from the lung to other organs. The clearance rates of particles from tracheobronchial airways are slowed by respiratory tract infections, but newer evidence implies that slow particle clearance from this region also exists in healthy lungs. Finally, hot spots of particle deposition are seen in hollow models, lung tissue, and dosimetric simulations. Local doses to groups of epithelial cells can be much greater than those to surrounding cells. The new insights challenge dosimetry scientists.

Entry kinetics and cell–cell transmission of surface‐bound retroviral vector particles

Transduction with recombinant HIV-1 derived lentivirus vectors is a multi-step process initiated by surface attachment and subsequent receptor-directed uptake into the target cell. We previously reported the retention of vesicular stomatitis virus G protein pseudotyped particles on murine progenitor cells and their delayed cell-cell transfer. To examine the underlying mechanism in more detail, we used a combination of approaches focused on investigating the role of receptor-independent factors in modulating attachment. The investigation of synchronized transduction reveals cell-type specific rates of vector particle clearance with substantial delays during particle entry into murine hematopoietic progenitor cells. The observed uptake kinetics from the surface of the 1 degrees cell correlate inversely with the magnitude of transfer to 2 degrees targets, corresponding with our initial observation of preferential cell-cell transfer in the context of brief vector exposures. We further demonstrate that vector particle entry into cells is associated with the cell-type specific abundance of extracellular matrix fibronectin. Residual particle-extracellular fibronectin matrix binding and 2 degrees transfer can be competitively disrupted by heparin exposure without affecting murine progenitor homing and repopulation. Although cellular attachment factors, including fibronectin, aid gene transfer by colocalizing particles to cells and disfavoring early dissociation from targets, they also appear to stabilize particles on the cell surface. The present study highlights the inadvertent consequences for cell entry and cell-cell transfer.

Particle removal by Northern bay scallops Argopecten irradians irradians in a semi-natural setting: Application of a flow-cytometric technique

The feeding activities of bivalve mollusks have direct impacts on suspended particles in nature. Feeding is also related to the carrying capacity of a particular system for maximal aquaculture production. Particle removal is known to be dependent upon particle characteristics, including size and type, because particle retention efficiency is size dependent, and bivalves are able to select particles actively to improve the quality of food ingested. Our goal was to quantify particle clearance by northern bay scallops of natural seston under semi-natural conditions, i.e., in raceway tanks receiving a constant flow of untreated, estuarine water. Particle clearance rate (CR) was determined based upon particle counts in tank inflow and outflow streams. A flow-cytometric technique was developed allowing rapid quantification of particles with different sizes and characterization by presence or absence of chlorophyll fluorescence simultaneously. CR varied greatly (ranging from 0.06 to 3.02 L h − 1 gDW − 1 ) among sizes and types of particles. CR of large particles was generally higher than that of the smaller particles. Under the specific conditions of this experiment, particle selectivity appeared to be ineffective because scallops did not show a higher CR on phytoplankton than on detritus. This study demonstrated the feasibility of this flow-cytometric approach to measure differential clearance of different particles in natural seston by suspension-feeding organisms.

Comparative utilization of phytoplankton and vascular plant detritus by the cockle Cerastoderma edule: digestive responses during diet acclimation

Contribution to the Theme Section 'Directions in bivalve feeding' ABSTRACT: Physiological components of food absorption (rates of particle clearance and ingestion and absorption efficiencies) were recorded in the cockles Cerastoderma edule fed variable concen- tration diets of phytoplankton (Isochrysis galbana) and detritus from salt-marsh vascular plants (Spartina maritina), after 2 and 12 d of acclimation to these diets. Corresponding digestive processes were also analysed, including determinations of gut passage time of food, gut fullness (GF) and digestive investments, the latter measured in terms of both metabolic faecal losses (MFL) and enzyme activities of the digestive glands. Digestive responses to increasing availability of phytoplankton included faster processing of food particles coupled to improved hydrolytic capacity of digestive glands that resulted in increased gut performance. Compared to phytoplankton, detritus utilization was constrained in the short-term by its refractory behaviour to digestion and the magnitude of meta- bolic faecal losses experienced by cockles fed these food materials. However, increased GF achieved during acclimation to detrital diets compensated for reduced digestibility, allowing for more food to be processed and thus cancelling out the effects of reduced passage time (and the consequent decline in absorption efficiency). Induction of the appropriate set of carbohydrases during the acclimation process resulted in increased amounts of reducing sugars released from natural substrates, with the additional benefit of diminishing the losses of endogenous materials accompanying each cycle of intracellular digestion.

Antioxidant and Immunity Activity of Water Extract and Crude Polysaccharide from Ficus carica L. Fruit

The antioxidative activities of water extract (WE) and crude hot-water soluble polysaccharide (PS) from Ficus carica L. fruit were investigated using various assays in vitro, including scavenging abilities on DPPH, superoxide and hydroxyl radicals and reducing power. The immunity activities of PS were evaluated using the carbon clearance test and serum hemolysin analysis in mice. In addition, total phenolics and flavonoids contents were also determined. Both WE and PS have notable scavenging activities on DPPH with the EC(50) values of 0.72 and 0.61 mg/ml, respectively. The PS showed higher scavenging activity than WE on superoxide radical (EC(50), 0.95 mg/ml) and hydroxyl anion radical (scavenging rate 43.4% at concentration of 4 mg/ml). The PS (500 mg/kg) also has a significant increase in the clearance rate of carbon particles and serum hemolysin level of normal mice. The results indicate that both WE and PS might be applicable in healthy medicine and food industry.

When Nanoparticles Get in the Way: Impact of Projected Area on In Vivo and In Vitro Macrophage Function

Previous reports by others establish that particle surface area is related to a change in macrophage function as measured by the ability to clear particles from the alveolar spaces. However, for nanoparticles the relation may not be strictly due to surface chemistry: The cumulative projected area of the particles may reflect the degree to which the inner or outer surface of the macrophage is shielded from other objects or molecules. We apply this alternative interpretation to in vitro measurements of macrophage uptake of 26-nm-diameter fluorescent beads and to in vivo data presented in a classic inhalation toxicology paper on nano-sized TiO2 particles. In their paper, Oberdörster et al. (Environ. Health Perspect. 102[suppl. 5]:173–179, 1994) reported that following inhalation exposure to 20-nm or 250-nm TiO2 particles, the half-times for alveolar clearance of polystyrene test particles were proportional to square centimeters of TiO2 particle surface per million macrophages; macrophage toxicity from TiO2 particle surface was assumed to be the cause of the decrease in the clearance rate of polystyrene test particles. When TiO2 particle projected area was incorporated into the in vivo macrophage dosimetry calculations, particle projected areas ranged in value from covering only a fraction (0.1) of the macrophage surface to covering the cell surface 4 times over. The observed decrease in macrophage mediated alveolar clearance of polystyrene test particles was directly related to the potential for TiO2 particles to mask the surface of the macrophage—a possibility that was visualized in vitro with confocal laser scanning microscopy.

Synthesis and Characterization of PEG-Based Ether−Anhydride Terpolymers: Novel Polymers for Controlled Drug Delivery

A series of biodegradable poly(ether−anhydrides) composed of poly(ethylene glycol) (PEG), sebacic acid (SA), and 1,3-bis(carboxyphenoxy)propane (CPP) were synthesized for use in advanced drug delivery applications. PEG (Mn = 8000 Da) was incorporated to reduce polymeric particle clearance rates by the immune system and improve particle resuspension and aerosolization efficiencies. CPP and SA were selected to render the polymer insoluble in water and allow control over polymer degradation and drug release rates. In particular, CPP incorporation caused a significant decrease in polymer degradation rates and release kinetics of model drugs incorporated into poly(ether−anhydride) microparticles. Terpolymers were synthesized with weight-average molecular weights over 65 kDa without catalyst. The first thermal transition in polymers containing ≤10 wt % PEG was ∼80 °C (well above typical storage conditions and body temperature), and there was no evidence of a glass transition (−100 to 200 °C). Several of the pol...

Fermentation and degradation in the rumen of dairy cows fed on diets consisting of silage from an intensively managed sward and silages from semi-natural grasslands

To assess the effect of grassland management on the ruminal digestion of silages, four lactating dairy cows, fitted with a rumen cannula, were fed diets consisting of concentrates and different grass silages. The grass silages consisted of intensively managed grass (IM) in variable proportions replaced by silages harvested from a ‘species-poor’ grassland managed to stimulate nesting of birds (SPP) or from a grassland managed to increase plant species diversity (SPR). The roughage part of the diets was composed completely of IM (100IM), or 200 g/kg (in dry matter) of IM replaced by SPP (20SPP) or 600 g/kg of IM replaced by SPP (60SPP), or SPR (60SPR). The pH in the rumen was highest on 60SPR and lowest on 100IM and 20SPP (P<0·05), whereas volatile fatty acids (VFA) concentrations were lowest on 60SPP and 60SPR and highest on 100IM (P<0·05). No differences in the ratio non-glucogenic: glucogenic volatile fatty acids were observed among the diets. The NH3 concentration was highest on 100IM and 20SPP and lowest on 60SPR (P<0·05), reflecting differences in CP intake. The concentration of uric acid in the urine (mg per kg metabolic body weight) was highest on 100IM (P<0·05). Rumen pool size of OM and DM did not differ among treatments, but pool size of NDF and IADF were highest on 60SPR (P<0·05). Passage rate was high on 100IM and 60SPR, but no significant differences with the other treatments were established. Also, no significant differences were observed in rates of degradation. Clearance rate of large particles was highest on 60SPP and differed significantly from 60SPR (P<0·05) only. No differences were observed in clearance rate of small particles. In conclusion, for most rumen fermentation characteristics measured in the study, no noticeably aberrant behaviour of the silages from semi-natural grassland was observed.

Long-Term Clearance Kinetics of Inhaled Ultrafine Insoluble Iridium Particles from the Rat Lung, Including Transient Translocation into Secondary Organs

Recently it was speculated that ultrafine particles (UFP) may translocate from deposition sites in the lungs to systemic circulation and whether long-term clearance differs between ultrafine and micrometer-sized particles. We have studied lung retention and clearance kinetics in 12 healthy male adult WKY rats up to 6 mo after an inhalation of 192Ir-radiolabeled, insoluble, ultrafine 15- to 20-nm iridium particles. Whole-body retention was followed by external gamma counting, and particle clearance kinetics were determined by excretion radioanalysis. Four rats each were sacrificed after 3 wk and 2 and 6 mo; all organs as well as tissues and the carcass were radioanalyzed to balance the entire deposited radioactivity of the particles. The most prominant fraction was retained in the lungs at each time point of sacrifice (26%, 15%, 6%, respectively), and clearance out of the body was solely via excretion. Extrapulmonary particle uptake did not continue to increase but decreased with time in liver, spleen, heart, and brain when compared to previous data obtained during the first 7 days after inhalation (Kreyling et al., 2002). UFP long-term lung retention derived from whole-body measurements was comparable to previously reported data using insoluble micrometer-sized particles (Bellmann et al., 1994; Lehnert et al., 1989). In addition, differential analysis including daily excretion data revealed a pattern of fractional particle clearance rate of the ultrafine iridium particles similar to that of micrometer-sized particles reported by Snipes et al. (1983) and Bailey et al. (1985).

Role of Leptothrix discophora in mediating metal uptake in the filter-feeding bivalve Mytilus trossulus (edulis).

The potential for filter-feeding bivalves to accumulate metals from a wide range of food sources is an important consideration when examining trophic transfer of metals up the food chain. The objective of this study was to determine the role of Leptothrix discophora in mediating metal uptake in the filter-feeding bivalve Mytilus trossulus. The bacterium L. discophora SP-6 was cultured in the absence or presence of Mn, allowing for a naturally formed Mn oxide sheath to develop. Secondary metals (Cd and Pb) were then added to the cultures, allowing for potential Cd and Pb adsorption to the Mn oxide sheath. Resulting bacterial aggregates of known diameter were then fed to the bivalve M. trossulus using a flow-through system. Initial concentrations of both Pb and Cd on the bacterium did not differ significantly in the presence or absence of the Mn oxide; conversely both Pb (F = 7.39, p < 0.0001) and Cd (F= 33.65, p < 0.0001) were found at lower concentrations in the mussel tissue when the Mn oxide was present. To determine whether these differences in metal uptake could be attributed to sorting by the mussel based on food quality, nutritional analysis was performed. Bacterial food matrixes containing Mn oxides were found to have significantly lower levels of carbon (F = 256, p < 0.0001). Particle clearance rates for the various food matrixes were positively correlated with organic content (R2 = 0.852, p > 0.008). The results of our study suggest that metal uptake in M. trossulus was significantly decreased for Cd with a similar trend for Pb when the SP-6 sheath contained Mn oxides. The mechanism mediating this differential uptake is best explained by food quality, in that a higher quality food source enhanced metal uptake due to an increased clearance rate of organic-rich particles by M. trossulus.

Efficiency of particle retention and clearance rate in the polychaete Sabellaria alveolata L.

The development of Sabellaria alveolata, a gregarious reef-building polychaete species, is maximal in Mont-Saint-Michel Bay (France), where trophic capacity is now threatened by increasing shellfish farming. As no data are available concerning the ecophysiological response of this species, the purpose of the present study was to obtain clearance rate and retention efficiency values to provide a first order of magnitude for the trophic role of this species. Data were obtained using a flow-through system with novel troughs suitable for 225 cm 2 reef blocks containing a mean number of 940±102 (S.E.) individuals. The experimental diet used consisted of a mixture of two live microalgae, Skeletonema costatum (3800 cell ml −1) and Isochrysis galbana (23 700 cell ml −1), chosen to cover a broad size range (2 to 16 μm equivalent spherical diameter, ESD), as determined by a particle counter. On the basis of a mean clearance rate of 0.7 l h −1 obtained with reef blocks, the mean rate for an individual was estimated at 7.5×10 −4 L h −1. Particles larger than 6 μm ESD were cleared with 100% efficiency, but S. alveolata was unable to retain particles smaller than 2 μm ESD. The results are compared with data obtained for other polychaete species, and clearance rate values are extrapolated to an entire reef. To cite this article: S. Dubois et al., C. R. Biologies 326 (2003).

New polymeric carriers for controlled drug delivery following inhalation or injection

Inhalation is gaining increasing acceptance as a convenient, reproducible, and non-invasive method of drug delivery to the lung tissue and/or the systemic circulation. However, sustained drug release following inhalation remains elusive, due in part to the lack of appropriate materials designed specifically for use in the lungs to control the release of bioactive compounds. To address this problem, we have synthesized a new family of ether-anhydride copolymers composed entirely of FDA-approved monomers, including polyethylene glycol (PEG). Sebacic acid, a hydrophobic monomer, was copolymerized with PEG in order to produce water-insoluble polymers capable of providing continuous drug release kinetics following immersion in an aqueous environment. Various amounts of PEG (5−50% by mass) were incorporated into the backbone of the new polymers to allow tuning of particle surface properties for potentially enhanced aerosolization efficiency and to decrease particle clearance rates by phagocytosis in the deep lung. The preparation of large porous particles with these new polymers was systematically approached, utilizing central composite design, to develop improved particle physical properties for deep lung delivery. Microparticles containing model drugs were made with sizes suitable for deposition in various regions of the lung following inhalation as a dry powder. Due to such properties as surface erosion (leading to continuous drug release profiles), erosion times ranging from hours to days (allowing control over drug delivery duration), and ability to incorporate up to 50% PEG in their backbone, these new systems may also find application as “stealth” carriers for therapeutic compounds following intravenous injection.

Modelling short-term responsive adjustments in particle clearance rate among bivalve suspension-feeders: separate unimodal effects of seston volume and composition in the scallop Chlamys farreri

Suspension-feeding behaviour in the scallop Chlamys farreri of 72±1 mm shell length was studied in response to wide variations in the amount and composition of suspended seston. Clearance rates (CR; l h −1) with which scallops removed all particles larger than 3.9 μm equivalent spherical diameter varied over an order of magnitude, initially increasing to maxima in separate unimodal relations with different measures of dietary abundance that included total particulate volume (VOL; mm 3 l −1), total particulate mass (TPM; mg l −1), particulate organic mass (POM; mg l −1), particulate organic carbon (POC; mg l −1) and chlorophyll a (CHL; μg l −1), before declining with further increases in seston concentration. Most variance in CR was associated with VOL (47%), compared with TPM (29%), POM (32%), POC (29%), PON (27%) and CHL (20%). This suggests morphological limits to feeding behaviour, as adjustments in CR were primarily dependent upon total seston volume, rather than any gravimetric measure of abundance. Nevertheless, stepwise regression indicated that VOL and CHL together accounted for as much as 58% of the variance in CR; more than for VOL alone ( p<0.001), and more than twice that explained by gravimetric measures of TPM, POM or CHL. The associated relation was best described by a combination of two unimodal curves, predicting that CR increased with food availability to a maximum of 7.1 l h −1 g −1 when VOL was 2.0 mm 3 l −1 and CHL was 5.3 μg l −1, before declining with further increases in either VOL or CHL. Response curves differed according to particle type. Most evidently, compared with silt-enriched diets, natural seawater contained about the same total chlorophyll l −1, but with much lower average volume, with the result that maximal CR was significantly higher in natural seawater. These findings establish highly flexible regulation of CR. They also indicate that to understand regulatory responses in feeding to a mixed suspension of different particles, it is necessary to measure the separate significant influences of particle volume and seston composition, when the range of experimental conditions must span the lower extreme of naturally occurring concentrations. We impress how our findings help to reconcile hitherto apparent differences between previous reports of bivalve suspension-feeding behaviour.

DEPOSITION OF FINE AND COARSE AEROSOLS IN A RAT NASAL MOLD

The objective of this study was to investigate the deposition characteristics of large, inhalable particles in rat nasal passages by determining the deposition efficiencies of these particles in a nasal mold of an F344 rat for steady-state and pulsating flow conditions. Particles with geometric diameters ranging from 0.5 to 4 µm and flow rates ranging from 100 to 900 ml/min were employed for simulated inspiratory and expiratory flow situations. The optically clear acrylic mold was fabricated from a life-size metal cast that comprised the nares, nasal cavity, pharynx, and larynx. Deposition efficiencies were calculated for each flow situation and plotted as functions of particle inertia. Inspiratory and expiratory deposition efficiencies were similar for a given flow condition. Deposition efficiencies for the cases of pulsating flows were markedly higher than those of steady flows. The results for pulsating flows indicated higher deposition efficiencies than were found in previous studies performed with live rats. These differences may be due to uncertainties in particle inhalability, clearance, and flow rate in the previous studies, as well as differences between the nasal geometries of live rats and the geometry of the nasal mold made from a postmortem cast. The results suggest that the pulsating nature of breathing is an important consideration when determining the deposition of fine and coarse particles.

Enhanced particle-feeding capacity of corals on turbid reefs (Great Barrier Reef, Australia)

Reef corals occur across a wide range of habitats, from offshore clear waters to nearshore sediment-laden environments. This study tests the hypothesis that corals from turbid nearshore areas have greater capacity to utilise suspended sediment as a food source than conspecifics from less turbid and midshelf areas. The hypothesis was tested on two common and widespread coral species on the Great Barrier Reef (Pocillopora damicornis and Acropora millepora). The particle clearance rates of samples from more turbid reefs were two-fourfold those of conspecifics from less turbid and midshelf reefs. Rates of sediment ingestion were generally a linear function of sediment load indicating no significant saturation within the concentration range of 1–30 mg dry weight l−1. Estimated assimilation efficiency of particulate 14C varied between 50 and 80%, and was maximised for midshelf A. millepora at the lowest sediment concentration, suggesting that heterotrophy is more efficient in oligotrophic habitats. Based on feeding-response curves, assimilation efficiencies, and published records of ambient particle concentrations, representatives of these species on turbid inshore reefs are 10–20 times more heterotrophic on suspended sediment than their conspecifics on less turbid and midshelf reefs.