Filtration Of Macromolecules Research Articles

Glomerular filtration of macromolecules: normal mechanisms and the pathogenesis of proteinuria.

Glomerular filtration of macromolecules: normal mechanisms and the pathogenesis of proteinuria.

Porous TEM windows fabrication using CsCl self-assembly

Thin non-porous silicon nitride membrane has been used for transmission electron microscopy (TEM) “windows” due to its transparency to high-energy electrons. However, to completely eliminate the background scattering, a porous membrane is desirable. Here the authors report the fabrication of porous silicon nitride membranes by CsCl self-assembly to form hemispherical islands, followed by “image reversal” via drying etching and liftoff steps. Through controlling the evaporated CsCl film thickness, the exposure time of the film in air, and the relative humidity of air, the authors were able to fabricate porous silicon nitride membranes with pore diameter and interpore spacing of order 100 nm. The pore diameter could be further shrunk by coating a conformal film onto the porous membrane. In addition, conductive porous TEM windows can be achieved by simply skipping the final metal removal step. Such a porous membrane would also find applications in separation or filtration of macromolecules or nanoparticles.

Ultrafiltration of an olive oil emulsion stabilized by an anionic surfactant

In this paper we report results on limiting flux in ultrafiltration of an oil in water emulsion stabilized by an anionic surfactant (sodium dodecyl sulfate). Whereas most of previous investigations report variations of filtration flux as a function of pressure at different flow rates, here we also consider the influence of surfactant/oil ratio and emulsion’s ionic strength. The present study clearly suggests that filtration of stabilized emulsions exhibits paradoxical experimental similarities with filtration of macromolecules. However, classical film models used for the latter case did not yield proper values for mass transfer coefficients. When using flux models to account for shear enhanced diffusion and pseudo-plastic behavior of the concentrated oil in water emulsions a good agreement between calculated and experimental mass transfer coefficient is obtained.

Opposite renal effects of a PGE1 analog and prostacyclin in humans

Renal effects of prostaglandins have been widely investigated in anesthetized animals, but in contrast only few studies have been devoted to healthy and diseased humans. Recently, both prostacyclin and a stable analog of PGE1, misoprostol, have been available for therapeutic purposes in clinical conditions associated with peripheral or renal vasoconstriction; however, the renal effects have not been defined. We have therefore studied the acute renal effects of PGI2 5 ng.kg/min intravenously and of misoprostol, a stable PGE1 analogue, 400 micrograms orally in two groups of respectively 8 and 12 healthy supine subjects on normal sodium diet using sodium, lithium, inulin, PAH and neutral dextran clearances. PGI2 induced a slight natriuretic effect, a systemic and renal vasodilation with a decrease in mean arterial pressure from 85.3 +/- 1.1 to 80.2 +/- 1.6 mm Hg (P < 0.01) and in renal vascular resistance from 94 +/- 6 to 75 +/- 5 mm Hg.min/ml (P < 0.001). GFR did not change whereas fractional clearance of dextran decreased over the 34 to 48 A radius range. Applying these changes on a hydrodynamic model of filtration of macromolecules through water-filled pores, we calculated that PGI2 decreased the glomerular transcapillary pressure gradient from 35 +/- 1 to 32 +/- 1 mm Hg (P < 0.001), decreased nonsignificantly the ultrafiltration coefficient Kf and did not affect the membrane parameters r0 and omega 0. Misoprostol had no natriuretic effect, induced slight renal vasoconstriction and moderate decrease in GFR from 124 +/- 9 to 114 +/- 10 ml/min.1.73 m2 (P < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Theoretical effects of network structure on glomerular filtration of macromolecules.

A parallel network model was developed to examine the effects of a distribution of capillary lengths on the filtration of macromolecules by the glomerulus. When networks having different distributions of capillary lengths (but similar values of single nephron glomerular filtration rate) were compared, the filtrate-to-plasma concentration ratio (theta s) for neutral macromolecules was found to increase as the vessel lengths became less uniform. Because anatomical studies have demonstrated that the glomerulus is in fact a heterogeneous network, this implies that the conventional modeling assumption of identical capillaries in parallel leads to an overestimation of effective pore sizes. However, simulations employing various pore-size distributions demonstrated that the expected errors in estimating membrane-pore parameters are generally negligible. Furthermore, the dependence of theta s on hemodynamic inputs such as glomerular plasma flow rate and transmembrane hydraulic pressure difference was insensitive to the assumed distribution of capillary lengths. We conclude that models based on dimensionally uniform capillary networks remain valid for interpreting clearance data for macromolecules.

Ultrastructure of the glomerular basement membrane, as visualized by lanthanum.

SummaryCortical tissues from the kidneys of rats were infused with a suspension of lanthanum hydroxide, or were placed in fixatives containing lanthanum to visualize intermolecular spaces in the glomerular basement membrane. Lanthanum particles were seen in aggregates throughout the basement membrane. The diameter of the aggregates varied between 20 and 200 A. The diameter of the majority of aggregates ranged from 40 to 75 A. Aggregates with diameters greater than 150 A were located mainly in the lamina rara interna, less in the lamina rara externa.It is concluded that the basement membrane is a random porous molecular filter and the lamina densa is the rate limiting structure in the glomerular filtration of macromolecules.