Rate Of Volume Increase Research Articles

A technique for the measurement of surface diffusion coefficient and activation energy of Ge adatom on Si(001)

A method for determining the surface diffusion coefficient and the activation energy of Ge adatoms on Si(001) has been developed. Ge self-assembled quantum dots (SAQDs) grown on a relaxed SiGe buffer layer preferentially nucleate over a network of buried 60° dislocations. The surface sites over the buried dislocations act as sinks of Ge adatoms. When the average dislocation spacing becomes larger than the surface diffusion length of Ge adatoms, denuded zones free of Ge SAQDs appear on both sides of buried dislocations and separating the preferentially nucleated SAQDs from the randomly nucleated ones. The denuded zone width and the inter-dot spacing of randomly nucleated SAQDs are completely dependent on the surface diffusion coefficient. By varying the substrate temperature during the growth, the activation energy for the surface diffusion can be determined from the equilibrium inter-dot spacing of the randomly nucleated Ge SAQDs. Moreover, the pre-exponential term in the diffusion constant can be determined by using Fick’s first law and the observation that the total incident flux of Ge adatoms impinging on the denuded zones equals the average rate of volume increase of SAQDs over dislocations. The diffusion coefficient of Ge adatoms on Si (001) is found to be Ds≅2.53×10−7 exp(−0.676±0.03 eV/kT) cm2/s in the temperature range from 650 to 725 °C.

Shape and volume change in the transtibial residuum over the short term: Preliminary investigation of six subjects

A preliminary investigation was conducted to characterize the magnitude and distribution of volume change in transtibial residua at two time intervals: upon prosthesis removal and at 2 week intervals. Six adult male unilateral transtibial amputee subjects, between 0.75 and 40.0 years since amputation, were imaged 10 times over a 35-minute interval with a custom residual limb optical scanner. Volume changes and shape changes over time were assessed. Measurements were repeated 2 weeks later. Volume increase on socket removal for the six subjects ranged from 2.4% to 10.9% (median 6.0% +/- standard deviation 3.6%). Rate of volume increase was highest immediately upon socket removal and decreased with time (five subjects). In four subjects, 95% of the volume increase was reached within 8 minutes. No consistent proximal-to-distal differences were detected in limb cross-sectional area change over time. Limb volume differences 2 weeks apart ranged from -2.0% to 12.6% (0.6% +/- 5.5%) and were less in magnitude than those within a session over the 35-minute interval (five subjects). Multiple mechanisms of fluid movement may be responsible for short-term volume changes, with different relative magnitudes and rates in different amputees.

Changes in portal vein flow after adult living-donor liver transplantation: Does it influence postoperative liver function?

In adult living donor liver transplantation, using small grafts in cirrhotic patients with severe portal hypertension may have unpredictable consequences. The so-called small-for-size syndrome is present in most series worldwide. The goal of this study was to prospectively evaluate the influence of hemodynamic changes on postoperative liver function and on the percentage of liver volume increase, in the setting of living donor liver transplantation. Twenty-two consecutive adult living donor liver transplantations were performed at our institution in a 2-year period. We measured right portal flow and right hepatic arterial flow with an ultrasonic flow meter in the donor, and then in the recipient 1 hour after reperfusion. Postoperative liver function was measured by daily laboratory work. We also performed duplex ultrasounds on postoperative days 1, 2, and 7. Liver volume increase was estimated by magnetic resonance imaging graft volumetry at 2 months posttransplantation. We compared the blood flow results with the immediate liver function and its liver volume increase rate at 2 months. There was a significant increase in portal flow in the recipients compared with the donors (up to fourfold in some cases). Higher portal flow increase rates significantly correlated with faster prothrombin time normalization and faster liver volume increases. Median graft volume increase at 2 months was 44.9%. The increase in blood flow to the graft is well tolerated by the liver mass not affecting hepatocellular function as long as the graft-to body weight ratio is maintained (>0.8) and adequate outflow is provided. (Liver Transpl 2003;9:564-569.)

Reproducibility of gastric tone, compliance and postprandial gastric accommodation assessed with barostat in dogs

(ramp phase) and was kept at this level tor 5 rain (tonic: phase), Adaptive accommodation during the toinc phase is the intragastric volume increase attained during the tonic phase, Maximum accommodation capacity is the rate of volume increase (ml/s) in the tonic phase. At'commodatinn time is the time from the start of the tonic phase to the end of adaptive accommodation. The volume response was investigated in each individual on two separate days, once during fasting conditions and once following 200 ml of a liquid meal (Nutridrink | 200 kcal/200 ml) given 15 min before the start of the distension. Results: In response to the test meal, healthy controls had a signibcant increase in maximum gastric volume (from 428-+ 60 to 734 _+ 31 ml, p = 0.0005), adaptive accommodation during tonic phase (from 223 -+ 37 to 435 -+ 41 ml, p = 0002), and in accomnmdation time (from 91 _+ i4 to 190 -+ 23 s, p = 0.003) The test meal had, hm,vever, no efi~.'ct on maximum accommodation capacity (2.4-+0,4 vs. 23_+0.2 mL/s, p=0+8) The most pronounced difi'erences between health3, controls and patients with tunctiona| dyspepsia were seen during lasting: adaptive accommodation during tonic phase (223-+ 37 ml in healthy persons and 132 -+ ]9 ml in patients, p = 004) and maximum accommodation capacity (2.4 _+ 0.4 vs. 0.8 _+ 0.1 ml/s, p = 0.0009), After tbe meal, there were no sigmficant differences between the groups. In patients with diabetes, the most pronounced difterences were seen after the meal: adaptive accommodation during the tonic phase (435 -+ 41 ml in heahhy controls vs. 274_+ 51 ml in diabetics, p = 0+03)+ Using these relatively low pressures the symptom scoring was inconsistent. Conclusion: This barostat technique allows detailed analysis of the gastric volume responses, Patients with functional dyspepsia and healthy controls differed significantly during lasting conditions concerning the rate and extent of adaptive accommodation during the tonic phase of distenmon, Diabetics, however, differed from controls mainly in adaptive accommodation during the tonic phase of distension after a meal.

Delayed liquid gastric emptying induced by electric stimulation of small intestine depends on nitric oxide pathway in conscious dogs

pressure in the 1200 ml balloon was raised by 3 mmHg/min from 1 mmHg to 12 mmHg (ramp phase) and was kept at this level tor 5 rain (tonic: phase), Adaptive accommodation during the toinc phase is the intragastric volume increase attained during the tonic phase, Maximum accommodation capacity is the rate of volume increase (ml/s) in the tonic phase. At'commodatinn time is the time from the start of the tonic phase to the end of adaptive accommodation. The volume response was investigated in each individual on two separate days, once during fasting conditions and once following 200 ml of a liquid meal (Nutridrink | 200 kcal/200 ml) given 15 min before the start of the distension. Results: In response to the test meal, healthy controls had a signibcant increase in maximum gastric volume (from 428-+ 60 to 734 _+ 31 ml, p = 0.0005), adaptive accommodation during tonic phase (from 223 -+ 37 to 435 -+ 41 ml, p = 0002), and in accomnmdation time (from 91 _+ i4 to 190 -+ 23 s, p = 0.003) The test meal had, hm,vever, no efi~.'ct on maximum accommodation capacity (2.4-+0,4 vs. 23_+0.2 mL/s, p=0+8) The most pronounced difi'erences between health3, controls and patients with tunctiona| dyspepsia were seen during lasting: adaptive accommodation during tonic phase (223-+ 37 ml in healthy persons and 132 -+ ]9 ml in patients, p = 004) and maximum accommodation capacity (2.4 _+ 0.4 vs. 0.8 _+ 0.1 ml/s, p = 0.0009), After tbe meal, there were no sigmficant differences between the groups. In patients with diabetes, the most pronounced difterences were seen after the meal: adaptive accommodation during the tonic phase (435 -+ 41 ml in heahhy controls vs. 274_+ 51 ml in diabetics, p = 0+03)+ Using these relatively low pressures the symptom scoring was inconsistent. Conclusion: This barostat technique allows detailed analysis of the gastric volume responses, Patients with functional dyspepsia and healthy controls differed significantly during lasting conditions concerning the rate and extent of adaptive accommodation during the tonic phase of distenmon, Diabetics, however, differed from controls mainly in adaptive accommodation during the tonic phase of distension after a meal.

The influence of donor age to graft volume increase rate in living donor liver transplantation

The influence of donor age to graft volume increase rate in living donor liver transplantation

Volumetric determination of progression in autosomal dominant polycystic kidney disease by computed tomography

Autosomal dominant polycystic kidney disease (ADPKD) is characterized by progressive renal enlargement and renal failure. We evaluated sequential radiocontrast-enhanced computed tomography (CT) scans to determine the rate of kidney enlargement in patients with ADPKD. Ten adult patients with ADPKD (4 men and 6 women) with initial serum creatinine levels </=1.6 mg/dL had at least two sequential CT scans more than three years apart. The mean patient age at the initial CT study was 33.8 years, and the mean initial serum creatinine concentration was 1.1 mg/dL (range 0.6 to 1.6 mg/dL; range of calculated creatinine clearances 60 to 135 mL/min/1. 73 m2). Total volume (Vt) was determined by manual tracing of renal areas in contiguous 5 to 10 mm thick axial CT slices for each kidney. The area of noncystic parenchyma (Vp) in each slice was determined by differential densitometry segmentation analysis of contrast-enhanced tissue, and total cyst volume (Vc) was the difference between Vt and Vp. The mean diameters of individual cysts were measured sequentially in selected cases. The mean initial Vt, Vp, and Vc values (+/- SEM) were 561 +/- 66, 243 +/- 19, and 317 +/- 57 mL per kidney, respectively. In 10 patients, after a mean of 5.7 years (range 3.3 to 11.9), Vt increased 323 +/- 79 mL (P < 0.01, range -25 to 1182 mL); the rate of volume increase was 53.9 +/- 10.4 mL/year/kidney (P < 0.001). In eight patients with repeat contrast-enhanced scans, Vt, Vp, and Vc increased 211 +/- 58 mL (P < 0.005), 26 +/- 11 mL (P > 0.05), and 185 +/- 52 mL (P < 0.01), respectively. In 19 individual spherical cysts selected in six patients, the mean initial volume was 15.0 +/- 7.2 mL (range 1.1 to 137 mL), and the average rate of volume increase was 0.52 +/- 0.21 mL/month (P < 0.025, range 0.02 to 4.15 mL/month). In five patients who eventually required dialysis, 11.2 years after the initial CT scan, the initial cyst/kidney volume ratio (combined for both kidneys) exceeded 0.43; four patients with lower cyst/kidney volume ratios had serum creatinine levels <1.5 mg/dL, 8.7 years after the initial CT scan. On the basis of this preliminary survey of archival material, we conclude that conventional contrast-enhanced CT scans can be used to quantitate volume components of progression in ADPKD. The rates of individual kidney and cyst enlargement are highly variable within and between patients, but overall, the values increase over time. The volume fraction of kidneys comprised of cysts may be a useful indicator of ADPKD progression.

Neonatal Necrotizing Enterocolitis: Possible Role of Probiotic Supplementation

Neonatal Necrotizing Enterocolitis: Possible Role of Probiotic Supplementation

Diagenesis in North Sea HPHT clastic reservoirs — consequences for porosity and overpressure prediction

Upper Jurassic clastic reservoirs of the Fulmar formation in the Central North Sea possess anomalously high porosities for their present day depth of burial. Reservoirs with the highest overpressures have the highest porosities, possess less macroquartz cement, and have significant secondary porosity. Quartz cementation in HPHT (High Pressure High Temperature) reservoirs has been inhibited by a combination of factors: high overpressure, limited fluid movement, presence of early grain coating cements, high pore fluid salinity, and possibly petroleum migration. Secondary porosity has contributed to reservoir quality, with an average of 4vol% extra porosity created. Quantitative prediction of porosity would require an improved depositional model for the Fulmar, accurate thermal and pressure modelling, and detailed knowledge of field filling and leakage histories. Theoretical calculations indicate that diagenetic reactions occurring in the Fulmar formation (smectite illitisation and quartz cementation), did not generate significant overpressure, because seal permeabilities were too high and the rate of volume increase associated with the reactions too small. Therefore diagenetic reactions can effectively be ignored when modelling overpressure generation in the Central North Sea, although cementation will affect rock permeability and rates of fluid dissipation.

Metabolic aspects of urinary bladder filling.

Urinary bladder compliance allows the bladder to fill to near capacity without a large increase in intravesical pressure. Bladder compliance is composed of two interrelated factors: passive characteristics of the connective tissue elements of the bladder, and active properties of the smooth muscle elements. The tension generated by the smooth muscle elements can significantly affect bladder compliance. This study utilized an in-vitro whole-bladder model in rabbits to determine the effects of hypoxia, alterations in calcium concentrations, and muscarinic agonists and antagonists on bladder capacity and compliance. The urinary bladder was excised together with a short segment of proximal urethra. A catheter was inserted into the bladder via the dome and the urethra was canulated with a saline-filled tube. The bladder was mounted in an isolated bath containing Tyrode's buffer. The catheter was connected to a pressure transducer to monitor the intravesical pressure and connected to a saline-filled i.v. bag. The weight of the saline bag was continually monitored. The height of the saline bag was set to 80 mmH2O above the baseline intravesical pressure. Bladder filling was started by opening the bladder to the saline reservoir. Intravesical pressure, rate of pressure increase, rate of volume increase, and maximal volume were digitally recorded. The bladder filling was repeated while the whole bladder was subjected to hypoxia, high calcium concentration, the presence of EGTA, carbachol, atropine and tetrodotoxin, respectively. Results are summarized as follows: (a) control bladder filling was biphasic, there was an initial rapid rise in intravesical pressure followed by a slower linear rise to the pre-set pressure; (b) hypoxia significantly decreased the initial rate of the rise in intravesical pressure, increased the rate of bladder filling, and significantly increased final bladder volume; (c) incubation of the bladder in the presence of EGTA also significantly decreased the initial rate of intravesical pressure rise, increased the rate of filling and also significantly increased the final bladder volume; (d) high concentrations of calcium increased the initial rate of rise in intravesical pressure; (e) carbachol significantly increased the rate of intravesical pressure rise, decreased the rate of bladder filling, and significantly decreased final bladder volume; (f) atropine and tetrodotoxin (TTX) had no effects on bladder filling. In summary, alterations in muscle tone had significant effects on bladder capacity and compliance.

Hexactinellid sponge ecology: growth rates and seasonality in deep water sponges

It has been well established that sponges play an important role in benthic ecology as abundant, large, sessile filter-feeders. However, the ecology of one group, the Hexactinellida, whose electrophysiology and cell biology is quite distinct from other Porifera, has received little attention due to the inaccessibility of their preferred deep water habitat. Now, a three year study of a population of the hexactinellid sponge Rhabdocalyptus dawsoni (Lambe, 1892) has been carried out in the fjords of British Columbia, Canada. Rhabdocalyptus was found to have a patchy distribution in Saanich Inlet, British Columbia, with local abundance reaching 5.3 individuals m −2. The mean length of the tube-like sponges in the inlet was 32 cm (an equivalent of 5.8 l volume) although sponges could reach 87 cm in length (36 l volume). The average growth rate of sponges measured over the course of 3 years was 1.98 cm year −1 (min. −0.76 cm year −1, max. 5.7 cm year −1) or 167 ml year −1 (min. −537 ml year −1, max. 856 ml year −1). The rate of tissue regeneration after artificial wounding in the field was 0.05±0.03 cm 2 day −1, some 40 times the rate of growth. No recruitment was observed during the study, but mortality of large individuals was seen. Using the calculated growth rate (average rate of increase in volume), the age of an average-sized sponge was estimated to be 35 years. With the assumption that growth rate is constant, large individuals (1 m in length) were estimated to be 220 years old. All sponges showed seasonal trends in sloughing of the debris-covered outer spicules during winter months (November to February). Increase in outer spicule coat occurred from March to October and sloughing corresponded to the end of seasonal phytoplankton blooms in October or November. These data suggest that hexactinellid sponges have life history strategies and growth rates similar to those of massive tropical and temperate demosponges and that, despite their deep water habitat, they experience seasonality which influences their growth rates and perhaps reproductive period.

EFFECTS OF HYPOXIA, CALCIUM, CARBACHOL, ATROPINE AND TETRODOTOXIN ON THE FILLING OF THE IN-VITRO RABBIT WHOLE BLADDER

The urinary bladder stores urine at low intravesical pressure and empties the urine efficiently and completely. Bladder compliance is the property that allows the bladder to fill to near capacity without a large increase in intravesical pressure. The current study utilized an in vitro whole bladder model to determine the effects of hypoxia, alterations in extracellular calcium concentration, carbachol and atropine on bladder capacity and compliance. Mature male New Zealand White rabbits were used in this study. The urinary bladder was excised from the rabbit together with a short segment of proximal urethra and mounted in a 400 ml. isolated bath containing Tyrode's buffer. Bladder filling was started by opening the bladder to a saline reservoir placed 80 cm. above the bladder. Intravesical pressure, rate of pressure increase, rate of volume increase, and maximal volume were digitally recorded. The bladder filling was repeated while the whole bladder was subjected to hypoxia, high calcium concentration, the presence of EGTA, carbachol, atropine and tetrodotoxin respectively. Results are summarized as follows: 1) Bladder filling was biphasic. There was an initial rapid rise in intravesical pressure followed by a slower rise. The final bladder volume averaged 46 ml. 2) Hypoxia significantly decreased the initial rate of the rise in intravesical pressure, increased the rate of bladder filling, and increased bladder volume by 43%. 3) Incubation of the bladder in the presence of EGTA also significantly decreased the initial rate of intravesical pressure rise, increased the rate of filling and increased bladder volume by 39%. 4) High concentrations of calcium increased the initial rate of rise in intravesical pressure. 5) Carbachol significantly increased the rate of intravesical pressure rise, decreased the rate of bladder filling, and decreased bladder volume. 6) Atropine and tetrodotoxin (TTX) had no effects on bladder filling. In summary, alterations in muscle tone had significant effects on bladder capacity and compliance.

EFFECTS OF HYPOXIA, CALCIUM, CARBACHOL, ATROPINE AND TETRODOTOXIN ON THE FILLING OF THE IN-VITRO RABBIT WHOLE BLADDER

Purpose The urinary bladder stores urine at low intravesical pressure and empties the urine efficiently and completely. Bladder compliance is the property that allows the bladder to fill to near capacity without a large increase in intravesical pressure. The current study utilized an in vitro whole bladder model to determine the effects of hypoxia, alterations in extracellular calcium concentration, carbachol and atropine on bladder capacity and compliance. Methods Mature male New Zealand White rabbits were used in this study. The urinary bladder was excised from the rabbit together with a short segment of proximal urethra and mounted in a 400 ml. isolated bath containing Tyrode's buffer. Bladder filling was started by opening the bladder to a saline reservoir placed 80 cm. above the bladder. Intravesical pressure, rate of pressure increase, rate of volume increase, and maximal volume were digitally recorded. The bladder filling was repeated while the whole bladder was subjected to hypoxia, high calcium concentration, the presence of EGTA, carbachol, atropine and tetrodotoxin respectively. Results Results are summarized as follows: 1) Bladder filling was biphasic. There was an initial rapid rise in intravesical pressure followed by a slower rise. The final bladder volume averaged 46 ml. 2) Hypoxia significantly decreased the initial rate of the rise in intravesical pressure, increased the rate of bladder filling, and increased bladder volume by 43%. 3) Incubation of the bladder in the presence of EGTA also significantly decreased the initial rate of intravesical pressure rise, increased the rate of filling and increased bladder volume by 39%. 4) High concentrations of calcium increased the initial rate of rise in intravesical pressure. 5) Carbachol significantly increased the rate of intravesical pressure rise, decreased the rate of bladder filling, and decreased bladder volume. 6) Atropine and tetrodotoxin (TTX) had no effects on bladder filling. Conclusion In summary, alterations in muscle tone had significant effects on bladder capacity and compliance.

Thermal Characteristics of a Hepatic Cryolesion Formedin Vitroby a 3-mm Implantable Cryoprobe

The objective of the investigation was to characterize the hepatic cryolesion formed with an implantable needle (3 × 100 mm) cryoprobe. This was used to produce cryolesions in isolated porcine liver tissue equilibrated to 37°C in a water bath. The shape, size, and temperature zones within the cryolesion and the effect of single versus repeated freeze–thaw cycles on cryolesion size were studied. The final shape of the cryolesion at 15–20 min freezing was cylindrical and its distal hemispherical end extended 8 mm beyond the tip of the cryoprobe. The rate of increase in maximum diameter was logarithmic and decreased from 4.7 mm/min during the first 5 min to 0.4 mm/min during the fourth 5-min period of freezing. By contrast, the rate of increase in volume was linear and ranged from 9.6 to 7.9 ml/min during the corresponding periods. The volume of the hepatic cryolesion after 20 min of continuous freezing was significantly greater than that of the cryolesion formed with 20 min of cumulative freezing interrupted by a 5-min spontaneous thaw. The ultimate temperatures reached and the cooling rates varied in different zones within the cryolesion depending on distances away from and alongside the cryoprobe. Diameter measurements taken in isolation do not reflect the actual growth rate of the cryolesion. Volume measurements define more accurately the amount of tissue frozen and leftin situ.Prolonged freezing beyond 20 min did not increase the diameter of the cryolesion. A single continuous freeze produces a larger cryolesion than two freeze–thaw cycles of the same freezing duration.

Measurements and a model of the outer hair cell hydraulic conductivity

The hydraulic conductivity of the cochlear outer hair cell WHO is central to the maintenance of the positive intracellular pressure necessary for its function as the cochlear amplifier. A mathematical model of osmotic water transport across the OHC membrane is formulated. The model relates the OHC hydraulic conductivity, L p , to the rate of volume change in response to osmotic stimuli. L p is evaluated from osmotic experiments in which isolated OHCs are exposed to an hypotonic solution. The rate of volume increase in response to the hypotonic challenge was determined by a morphometric analysis of video images of cells. L p was found to be about 10 −14 m s −1 1 Pa −1 or equivalently, P f ∼ 10 −4 cm s −1. This is on the low side of values reported for different lipid bilayers and is 2 orders of magnitude lower than the hydraulic conductivity of red blood cells. The relation of the low OHC hydraulic conductivity to the composition and morphology of its membranes is discussed.

Problems and priorities in epidemiologic research on human health effects related to wiring code and electric and magnetic fields: J. Siemiatycki. Environmental Health Perspectives Supplements, 101(Suppl. 4)

To investigate the relationship between waiting time (WT) and disease progression in patients undergoing stereotactic body radiotherapy (SBRT) for lung adenocarcinoma (AD) or squamous cell carcinoma (SQ).201 patients with Stage I AD or SQ undergoing SBRT between January 2004 and June 2010 were analyzed. The WT was defined as the interval between diagnostic computed tomography before referral and computed tomography for treatment planning or positioning before SBRT. Tumor size was measured on the slice of the longest tumor diameter, and tumor volume was calculated from the longest diameter and the diameter perpendicular to it. Changes in tumor volume and TNM stage progression were evaluated, and volume doubling time (VDT) was estimated.The median WT was 42 days (range, 5–323 days). There was a correlation between WT and rate of increase in volume in both AD and SQ. The median VDTs of AD and SQ were 170 and 93 days, respectively. Thirty-six tumors (23%) did not show volume increase during WTs >25 days. In 41 patients waiting for ≤4 weeks, no patient showed T stage progression, whereas in 25 of 120 (21%) patients waiting for >4 weeks, T stage progressed from T1 to T2 (p = 0.001). In 10 of 110 (9.1%) T1 ADs and 15 of 51 (29%) T1 SQs, T stage progressed (p = 0.002). N stage and M stage progressions were not observed.Generally, a WT of ≤4 weeks seems to be acceptable. The WT seems to be more important in SQ than in AD.

Micromechanical deformations in particulate filled thermoplastics: volume strain measurements

Volume strain measurements were carried out on PP composites containing different CaCO3 fillers. During deformation, a volume increase was detected which could be divided into two linear sections as a function of elongation. Comparison of data with existing theories has shown that in the first part, mostly elastic deformation takes place and the slope can be related to the Poisson's ratio of the composite. Scanning electron microscopy revealed that in the second stage, the dominating micromechanical deformation process is debonding. Void formation is initiated at a certain stress which approximately corresponds to the yield stress of the composites, but data in the literature and model calculations indicate that separation of the matrix/filler interface may start at lower stresses. Initiation stress depends on the particle size of the filler and on interfacial interactions. The rate of volume increase has non-linear dependence on the volume fraction of the filler. Volume strain measurements reflect micromechanical deformations well, but further study is needed to explain contradictions between experimental results and theoretical predictions.

Cultured bovine corneal endothelial cells express CHIP28 water channels

Cultured bovine corneal endothelial cells (CBCEC) transport fluid from the basal to the apical surface. In this study, we examined whether the plasma membranes of these cells have water channels. We cultured BCEC on glass plates and monitored the intensity of the light scattered (IS) by the cells. We determined the kinetic constant (k) of the change in IS on exposure to a 10% hypoosmotic challenge to calculate the osmotic permeability (Pf) of the plasma membrane. At 37 degrees C, we found values of k = 0.68 +/- 0.07 s-1 and Pf = 93.3 +/- 33 microns/S (n = 13). The sulfhydryl reagent p-chloromercuribenzenesulfonate (pCMBS; 1 mM) reduced Pf by 75%; 5 mM dithiothreitol reversed such inhibition. The activation energy (Ea) of Pf in the range 10-37 degrees C was 4.7 +/- 0.7 kcal/mol (n = 5). The high Pf, values, the inhibition by pCMBS, and the low Ea strongly suggest the presence of water channels. Therefore, we tested whether the injection of poly(A)+ RNA prepared from CBCEC into Xenopus laevis oocytes results in the expression of water channels. Four days after injection, we measured oocyte Pf values from the rate of volume increase on exposure to hypoosmotic medium. In control oocytes injected with 50 nl of water, Pf was 13.4 +/- 0.3 microns/S (n = 63). In oocytes injected with poly(A)+ RNA (50 ng/oocyte in 50 nl water), Pf was 40.9 +/- 1.6 microns/S (n = 72).(ABSTRACT TRUNCATED AT 250 WORDS)

Sedimentation in a river dominated estuary

ABSTRACTThe Mgeni Estuary on the wave dominated east coast of South Africa occupies a narrow, bedrock confined, alluvial valley and is partially blocked at the coast by an elongate sandy barrier. Fluvial sediment extends to the barrier and marine deposition is restricted to a small flood tidal delta.Sequential aerial photography, sediment sampling and topographical surveys reveal a cyclical pattern of sedimentation that is mediated by severe fluvial floods which exceed normal energy thresholds. During severe floods (up to 10x 103 m3 s−1), lateral channel confinement promotes vertical erosion ofbed material. Eroded material is deposited as an ephemeral delta in the sea. After floods the river gradient is restored within a few months through rapid fluvial deposition and formation of a shallow, braided channel. Over an extended period (approximately 70 years) the estuary banks and bars are stabilised by vegetation and mud deposition. Subsequent downcutting in marginal areas transforms the channel to an anastomosing pattern which represents a stable morphology which adjusts to the normal range of hydrodynamic conditions. This cyclical pattern of deposition produces multiple fill sequences in such estuaries under conditions of stable sea level.The barrier and adjacent coastline prograde temporarily after major floods as the eroded barrier is reformed by wave action, but excess sediment is ultimately eroded as waves adjust the barrier to an equilibrium plan form morphology. Deltaic progradation is prevented by a steep nearshore slope, and rapid sediment dispersal by wave action and shelf currents.During transgression, estuarine sedimentation patterns are controlled by the balance between sedimentation rates and receiving basin volume. If fluvial sedimentation keeps pace with the volume increase of a basin an estuary may remain shallow and river dominated throughout its evolution and excess fluvial sediments pass through the estuary into the sea. Only if the rate of volume increase of the drowned river valley exceeds the volume of sediment supply are deep water environments formed. Under such conditions an estuary becomes a sediment sink and infills by deltaic progradation and lateral accretion as predicted by evolutionary models for microtidal estuaries. Bedrock valley geometry may exert an important control on this rate of volume increase independently of variations in the rate of relative sea level change.If estuarine morphology is viewed as a function of the balance of wave, tidal and fluvial processes, the Mgeni Estuary may be defined as a river dominated estuary in which deltaic progradation at the coast is limited by high wave energy. It is broadly representative of other river dominated estuaries along the Natal coast and a conceptual regional depositional model is proposed. Refinement of a globally applicable model will require further comparative studies of river dominated estuaries in this and other settings, but it is proposed that river dominated estuaries represent a distinct type of estuarine morphology.

Expression of multiple water channel activities in Xenopus oocytes injected with mRNA from rat kidney.

To test the hypothesis that renal tissue contains multiple distinct water channels, mRNA prepared from either cortex, medulla, or papilla of rat kidney was injected into Xenopus oocytes. The osmotic water permeability (Pf) of oocytes injected with either 50 nl of water or 50 nl of renal mRNA (1 microgram/microliter) was measured 4 d after the injection. Pf was calculated from the rate of volume increase on exposure to hyposmotic medium. Injection of each renal mRNA preparation increased the oocyte Pf. This expressed water permeability was inhibited by p-chloromercuriphenylsulfonate and had a low energy of activation, consistent with the expression of water channels. The coinjection of an antisense oligonucleotide for CHIP28 protein, at an assumed > 100-fold molar excess, with either cortex, medulla, or papilla mRNA reduced the expression of the water permeability by approximately 70, 100, and 30%, respectively. Exposure of the oocyte to cAMP for 1 h resulted in a further increase in Pf only in oocytes injected with medulla mRNA. This cAMP activation was not altered by the CHIP28 antisense oligonucleotide. These results suggest that multiple distinct water channels were expressed in oocytes injected with mRNA obtained from sections of rat kidney: (a) CHIP28 water channels in cortex and medulla, (b) cAMP-activated water channels in medulla, and (c) cAMP-insensitive water channels in papilla.