Rate Of Fluid Movement Research Articles

Mathematical Modeling of Marker Influx and Efflux in Cells

The tumor promoter, phorbol 12-myristate 13-acetate (PMA), affects the processing of fluid that enters a cell from the ambient medium. Previous work showed that marker accumulates to a higher level in PMA-treated than in untreated cells. Since PMA also affects the physical activity of the membrane and stimulates the normal process of taking up extracellular fluid, called endocytosis, it is important to learn whether the perturbations in fluid processing can be attributed entirely to a change in the cell’s limiting membrane. To this end, a model for fluid uptake and processing was developed and applied to experiments in which a marker for extracellular fluid was added to cells. From previous work on marker accumulation, it was deduced that there were at least two functional compartments involved in fluid movement. Compartment I is a rapidly filling and rapidly recycling compartment. Compartment II is a slowly filling and emptying compartment. Three routes of vesicle traffic must be considered, one mediating influx from the ambient medium into compartment I, a second, efflux from compartment I to the medium, and a third efflux from compartment I into compartment II. Using earlier models for processing, workers found it difficult to estimate rates of movement through either of the latter routes, as well as the volume of compartment I. The difficulty arises from the fact that only one kinetic constant can be estimated directly from data, namely the instantaneous uptake rate. The remaining data depend on measuring the total mass of marker in the cells. Since the concentration of marker in the cell changes continuously, it is advantageous to employ differential equations to simulate the tracer movement. By applying the model to experimental values, we found estimates for all three rates of fluid movement and the volume of compartment I. It is thought that the model will enable us to determine whether apparent alterations in the time course of uptake arise solely from altered properties of the limiting membrane.

Solute transfer in fluid flow in permeable tubes with application to flow in glomerular capillaries

A mathematical model for solute transfer in an ultrafiltering glomerular capillary has been proposed. The solute transfer, by diffusion and convection, within and across the tube wall has been considered. Effects due to the presence of red cells are neglected and the blood is assumed to be Newtonian fluid with constant viscosity. The rate of fluid movement at the wall is assumed to be proportional to the difference between the net hydrostatic and osmotic forces — Starling's law. The velocity and concentration profiles, at different positions along the axis, the axial distribution of hydrostatic and osmotic pressures and the total solute clearance have been obtained. It is found that the osmotic pressure has relatively greater influence on capillary mass transfer than the hydrostatic pressure. Radial concentration gradients of considerable order have been observed, particularly near the entrance portion of the tube. The radial concentration gradient increases with ultrafiltration parameter and decreases, as the diffusion coefficient increases. The influence of transmittance coefficient (solute wall permeability coefficient) is found to be predominant at higher ultrafiltration rates (higher concentration difference across the membrane). The generalized nature of the present model has been illustrated by obtaining some of the existing results as the particular cases of this model. Using relevant data, the physiological implications of some of the obtained results have been briefly discussed.

Fluid movement in bone: Theoretical and empirical

Evidence from the literature and from our laboratory demonstrates a pronounced and rapid flow of fluids and associated solutes through the extravascular spaces in bone. Minutes after injection, large molecules such as ferritin and horseradish peroxidase (HRP) have been localized throughout the osteocytic lacunae and canaliculi of cortical bone in the chick, rat and dog. Patterns of marker movement preclude diffusion as the mechanism for solute movement and suggest a centrifugal bulk flow of fluids. We have developed a computer model of bone fluid flow that has led to the conclusion that the pattern and rate of fluid movement is governed by the pressure differential across the bone, the vascular architecture, and the porosity of the mineralized matrix. The validity of simulations in which a substance is injected and monitored over time has been tested by comparisons with actual injections of markers in the rat. Evidence is presented for a relationship between blood flow and bone dynamics in growth, repair and pathology of bone. We employed the tail suspension model of weightlessness in the rat to test the effect of posture on the perfusion of cortical bone using injections of HRP. Data indicated that perfusion of the femur was reduced by this treatment. We propse a “rheostat” mechanism, which suggests that bone perfusion may set limits for bone growth and remodeling. Therefore, bone mass reflects the ability of the vasculature to supply oxygen and nutrients to the cells on and within the mineralized matrix.

Simulating the Grain-Size Distribution of Wisconsinan Age Glaciofluvial Sediments: Applications to Fluid Transport

A sedimentary deposition model, SEDSIM, was used to simulate the deposition of glaciofluvial sediments in south-central Wisconsin. These types of deposits are present at or near the surface over much of the northern United States and have a high contamination potential. They also represent relatively recent analogs for ancient braided stream systems. Sixty sediment samples were used to determine the average sediment properties for a facies assemblage located 8-10 km from the ice margin. A regional depositional system was simulated, using SEDSIM, to determine the range of input values that reproduced the observed average sediment characteristics. Progressively smaller scale models were constructed to produce more detailed estimates of the grain-size distribution. the grain-size estimates from the finest scale model were translated into relative hydraulic conductivity values using the method of Hazen. The resulting conductivities were incorporated into a fluid flow model to illustrate the control that heterogeneity of petrologic properties has on the direction and rate of fluid movement. This work indicates that a wide range of input parameters will reproduce the bulk sediment properties. Furthermore, small-scale features may not be reproduced under the assumptions incorporated in the current SEDSIM code. Thus, for sedimentary depositional models to be used tomore » predict permeability and porosity distributions, or to interpret paleo-flow conditions, one must determine calibration targets that are more sensitive to flow parameters than bulk grain-size distributions.« less

The role of low-permeability rocks in regional flow

Summary The role of low-permeability rocks in determining fluid migration within sedimentary basins has been shown to be crucial for deriving the direction and rate of fluid movement. The magnitude of the flows depends on the geometry of the sedimentary basin and on the bulk hydrogeological properties of the various strata and their relative values. Measurements of head and pore-water compositions of argillaceous formations show separate evidence for the existence of cross-formational flow resulting in groundwaters of mixed origins. Numerical and analytical models have been developed and applied to some basinal systems in England. They have been used to assess the directions of groundwater flow likely to be encountered by repository site investigation programmes and to aid in the interpretation of groundwater head and chemistry data. Such flow models still require detailed validation. Our knowledge of the flow mechanism and the physical properties of mudrocks at depth is still elementary, but the indications are that the role of low-permeability rocks in controlling fluid migration has been much underestimated.

Buffering Capability of Mineral Assemblage (Feldspar + Kaolinite + Quartz) and Its Application to Predicting Illite Occurrence in Arkosic Sandstones: ABSTRACT

Studies of phase relationships using the activity diagrams involving feldspar, illite, kaolinite, and gibbsite (or boehmite) reveal that the common mineral assemblage of feldspar, kaolinite, and quartz found in arkosic sandstone provides a strong driving force to change the fluid chemistry to conditions thermodynamically favoring illite formation. The driving force involves three major diagenetic reactions: the hydrolysis of feldspar with acidic fluid, the reaction of kaolinite with alkaline fluid, and the saturation of the fluid with respect to quartz. The first and second reactions result in, respectively, the increase and decrease of K/sup +//H/sup +/ activity ratio, whereas the third reaction tends to maintain the Si(OH)/sub 4/ activity in the pore fluid. The resultant fluid chemistry of these reactions coincidentally falls in the stability field of illite. This relationship occurs over a wide range of pressure and temperature conditions with low fluid to rock ratio. Experimental results show that an increase in the fluid to rock ratio will decrease the rate that the fluid chemistry approaches the illite stability field. The effectiveness of the buffering capability, therefore, depends on the relative rate of fluid movement and fluid/rock reaction. This study demonstrates that the most likely condition for illite formation ismore » a quartzofeldspathic system involving the presence of kaolinite and low fluid movement. In the absence of these conditions, the opportunity to precipitate illite in the pore space is significantly reduced. The commonly observed illitization of kaolinite or feldspar during burial diagenesis could be caused simply by the reduced influx of fluid (with any compositions: alkaline, neutral, or acidic) due to deep burial of the sandstone.« less

Experimental retinal detachment. VI. The permeability of the blood-retinal barrier.

Fluorophotometry was used to study the permeability of the blood-retinal barrier in six monkeys with stable rhegmatogenous retinal detachments. Fluorescein transport was inhibited by probenecid. The rate of fluorescein disappearance (KvVv) was determined following intravitreal injection. In a separate experiment the equilibrium vitreous-plasma concentration ratio (Cv/Cp) was determined following intraperitoneal administration. Expressed in equivalent volumes of vitreous, the rate of fluorescein diffusion across the blood-retinal barrier (K'vVvCv/Cp) was 0.29 microL/min in control eyes and 0.73 microL/min in detached eyes. The rate of fluid movement across the blood-retinal barrier (K'vVv) [1 - (Cv/Cp)] was 2.89 microL/min in control eyes and 6.38 microL/min in detached eyes. Posterior movement of fluid contributes to retinal apposition under normal conditions and accounts for the rapid resolution of retinal detachment following closure of the retinal hole.

The rate of translymphatic endothelial fluid movement in the canine kidney

The rate of fluid movement across the lymphatic endothelial wall, as measured in microliters per minute per square centimeter of endothelium, is estimated from published and unpublished data on the canine kidney. Published values for total renal lymph flow, derived by several different techniques, are reviewed and a mean value of 0.3 ml/min/100 g is taken as a reasonable working estimate. Morphologically the intrarenal lymphatic system is considered to consist of four types of lymphatics—intralobular, interlobular, arcuate, and interlobar—and the endothelial surface area of these is calculated by geometric formulas. Thus each of the four types of lymphatics is considered as a single cylinder having a radius equal to the mean radius of that type of lymphatic and a length equal to the total length of all lymphatics of that type. The convex surface area ( A c) of interlobular and intralobular vessels is calculated by the formula A c = 2v r , where the radius ( r) is measured in tissue sections and the volume ( v) is derived from published volume density data. A c for arcuate and interlobar lymphatics is estimated by the formula A c = n(2 πrl), where n is the number and r is the radius of these lymphatics, as obtained from tissue sections, and l is the average length of the associated arteries. By these methods, values of A c for intralobular, interlobular, arcuate, and interlobar lymphatics of 59, 87, 34, and 15 cm 2, respectively, are calculated. All four types are considered, on ultrastructural evidence, to be vessels that participate in the transport of lymph. By dividing total renal lymph flow by the total lymphatic endothelial surface an approximate value of 1 μl/min/cm 2 is obtained for the average rate of fluid transfer across lymphatic endothelial cells in the control dog kidney.

The hydraulic conductivity of rabbit ciliary epithelium in vitro

The rate of fluid movement across rabbit ciliary body in vitro has been measured as a function of applied hydrostatic pressure. Previous studies from other laboratories carried out with the ciliary body clamped between two half chambers have yielded a value of 4600 ± 600 μm/sec. We have presently reproduced those results by using a similar mounting procedure. On the other hand, however, we report the development of a technique for edge-damage-free mounting of the ciliary body with which the tissue is not clamped and tissue glue is employed in order to achieve a proper seal. With this last procedure, the values thus obtained for the hydraulic conductivity were much lower than the previous ones, namely, 210 μm/sec for pressure applied on the stromal side of the ciliary epithelium (pressure range: 0–10 cm H 2O, n = 13; T = 37°C), or 109 μm/sec (pressure difference range: 0–31 cm H 2O) for pressure applied from the aqueous side. We conclude that the notion of aqueous production by ultrafiltration cannot be supported by the present results.

266 DEVELOPMENTAL CHANGES IN BASOLATERAL MEMBRANE (BLM) OF RABBIT PROXIMAL CONVOLUTED TUBULE (PCT)

The maturational increase in proximal tubular sodium reabsorption is associated with several developmental changes: 1) decrease in hydraulic conductance 2) decrease in leakiness of tight junction 3) increase in surface area of BLM. The BLM provides a barrier to fluid reabsorption but its role is poorly characterized because reabsorption studies relate primarily to fluid movement across the entire transepithelial surface. To evaluate developmental changes in the rate of fluid movement across the BLM, 53 single early PCT with collapsed lumens were isolated from the outer cortex of rabbit kidneys and both ends tightly crimped in pipets. BLM surface area and rate of change of cell volume assessed by cell diameter in 10−4M ouabain were measured in the same tubule segment. Rates of swelling were used to compare trans BLM fluid movement during development. Tubules from 2-17 days were of similar maturity as judged by swelling rate and BLM surface area, but swelling rate and surface area increased by adulthood. We conclude that increases in trans BLM fluid movement relate primarily to surface area and not necessarily to intrinsic changes in membrane permeability.

Fluid transport across the canine tracheal epithelium.

We measured the rate of fluid movement across the tracheal epithelium of the dog by an electrical method, modified from that originally described by Wiedner (Rev. Sci. Instrum. 47: 775-6, 1976). The base-line volume flow (Jv) from the submucosa to the mucosa was 44 +/- 23 nl.min-1.cm-2 (mean +/- SE; n = 6). In only three of the tissues was the resting Jv significantly greater than zero. Stimulation with 2 X 10(-3) M aminophylline (a drug that we have shown stimulates Cl secretion under short-circuit conditions) increased Jv in all tissues to a mean of 137 +/- 29 nl.min-1.cm-2 (P < 0.001). We also measured the unidirectional fluxes of Cl with the tissue at its spontaneous electrical potential. During the base-line period, the net flux of Cl was not significantly different from zero. During stimulation with aminophylline, Cl secretion increased to a mean of 1.44 +/- 0.50 microneq.cm-2.h-1. Comparison of the stimulated values of Jv and net Cl secretion suggests that fluid secretion by the trachea is isotonic during stimulation with aminophylline.

Permeability of urinary bladder of Rana cancrivora to urea in the presence of oxytocin.

1. When Rana cancrivora collected from fresh water had been exposed for 3 days to saline solutions having osmolalities from 280 to 690 m-osmole/kg, urea concentrations in plasma and urine appeared to come into equilibrium, and were from 70 to 200 m-mole/l.2. Plasma urea level of fresh water R. cancrivora (48 m-mole/l.) was doubled (82 m-mole/l.) after 8 hr of exposure to 270 m-osmolal saline. It continued the same after 24 hr of exposure.3. When isolated urinary bladders of R. cancrivora were exposed to Ringer on the serosal aspect and one-fifth Ringer on the mucosal aspect, then in response to this osmotic difference of 190 m-osmole/kg, the rate of fluid movement (mucosa to serosa), which was 10.3(+/-2) mul./cm(2).hr, was not significantly altered when up to 60% of the NaCl of the Ringer solution was substituted by urea.4. Under the same circumstances, when oxytocin (50 m-u./ml.) was present in the serosal solution, the rate of fluid movement (mucosa to serosa) was 133.2(+/-7.9) mul./cm(2).hr in the absence of urea; it was progressively decreased by the presence of urea until, when 80% of the NaCl had been substituted by urea, the rate of fluid movement was reduced to 14.5(+/-4.0) mul./cm(2).hr.5. The diminished rate of fluid movement under the above circumstances could not be correlated with serosal urea concentration, with serosal availability of Na(+), nor with Na(+) concentration difference across the bladder wall. It appeared to be directly related to the ;non-urea osmotic difference' across the bladder wall provided by solutes other than urea.6. When isolated bladders were exposed to an osmotic difference of 190 m-osmole/kg, but having 25 mM urea present in the mucosal solution, then fluid moved from mucosa to serosa at a rate of 10.4(+/-1.3) mul./cm(2).hr in the absence of oxytocin and 124(+/-9) mul./cm(2).hr when oxytocin (50 m-u./ml.) was present. In the former case no urea passed across the bladder wall, but in the latter case urea passed from mucosa to serosa at a rate of 3.16(+/-0.3) mumole/cm(2).hr. The fluid moving from mucosa to serosa thus contained urea 25.5 m-mole/l.7. Vasotocin (10(-9)M), which is equipotent with oxytocin (50 m-u./ml.) in affecting permeability of the isolated urinary bladder to water, was also equipotent in producing a reduced rate of water fluid movement in the presence of 40% urea (vasotocin, 63 mul./cm(2).hr; oxytocin, 59 mul./cm(2).hr).8. When groups of frogs were cystectomized, and other groups of frogs were sham-operated, then after 48 hr of exposure to fresh water or to 300 m-osmolal saline the sham-operated frogs had plasma urea level raised from 20 m-mole/l. (fresh water) to 42 m-mole/l. (saline), while the cystectomized frogs had 20 m-mole/l. (fresh water) and 26 m-mole/l. (saline).9. The hypothesis is presented that hormone-induced permeability of the urinary bladder to urea contributes to the immediate adjustment of plasma urea level by which R. cancrivora survives when exposed to high environmental salinity.

Relationship of fluid transport through the dentin to the incidence of dental caries.

The rate of fluid movement in the teeth of 28-day-old rats is inversely related to the incidence of dental caries after 13 weeks of the same diets. The early hypomineralization found in the dentin at 28 days is a result of altered metabolism imposed by a reduced rate of fluid transport in the rats fed a cariogenic diet.