Showing papers by "Channing R. Robertson published in 1975"
TL;DR: Electrostatic repulsion of charged macromolecules by some component of the glomerular capillary wall, perhaps the negatively charged sialoprotein which coats glomersular epithelial cells, might account for the enhanced transmural passage of albumin.
374 citations
TL;DR: This sensitivity of fractional dextran clearance to changes in plasma flow indicates that dextrans are transported across the capillary not only by bulk flow but also to an important extent by diffusion.
290 citations
TL;DR: To examine the coupling between macromolecular solute transport and the determinants of glomerular filtration rate, these flux equations were combined with mass balance relations which allow for variations in the transmembrane driving forces along aglomerular capillary.
151 citations
TL;DR: Reactor conversion data over a wide range of operating conditions agrees well with predictions obtained from a mathematical model developed previously, and β-galactosidase immobilized by this technique was found to retain 100% activity for 60 hours of continuous reactor operation, and for 140 days when stored at 3°C.
Abstract: An enzyme immobilization technique employing enzyme sequestration within the porous support regions of asymmetric hollow fiber membranes is described and experimentally evaluated. Reactor conversion data over a wide range of operating conditions agrees well with predictions obtained from a mathematical model developed previously. β-galactosidase immobilized by this technique was found to retain 100% activity for 60 hours of continuous reactor operation, and for 140 days when stored at 3°C. The effects on reactor performance of (1) enzyme adsorption by the membrane, and (2) axial redistribution of enzyme accompanying radial flow of fluid through the fiber wall, have been evaluated; neither process significantly alters conversion kinetics or efficiency for the substrate/enzyme system investigated.
67 citations
TL;DR: Findings provide an attractive explanation for the general tendency for filtration fraction to vary directly with hematocrit in anemic and polycythemic states in man.
Abstract: This study was undertaken in an effort to examine the effects of selective variations in systemic hematocrit on the preglomerular, glomerular, and postglomerular micocirculation in the rat. By isovolemic exchange transfusions, systemic hematocrit (control 51 ml/100 ml) was either reduced (21 ml/100 ml, N equal 7 rats) or elevated (62 ml/100 ml, N equal 7). Single nephron glomerular filtration rate varied inversely and filtration fraction varied directly with the changes in hematocrit. The fall in filtration fraction with decreased hematocrit was due to a decline in the measured glomerular transcapillary hydraulic pressure difference and to a marked increased in the initial glomerular plasma flow rate. Afferent (RA)and efferent (RE) arteriolar resistance declined with the fall in hematocrit; RA fell proportionately more than did RE. The rise in filtration fraction with the elevation in hematocrit was due to a marked increase in in part due to a relatively greater rise in RE than in RA. These findings provide an attractive explanation for the general tendency for filtration fraction to vary directly with hematocrit in anemic and polycythemic states in man.
62 citations
TL;DR: Findings are interpreted as evidence for net water uptake by the vasa recta in the renal inner medulla for which the driving forces are the transcapillary hydraulic and oncotic pressure differences.
Abstract: The vasa recta are thought to play an important role in the transfer of water andsolutes within the renal medulla Hydraulic pressures were measured in vasa recta onthe surface of the exposed papil
39 citations
TL;DR: The important influence exerted by image forces on ion transport in lipid bilayer membranes compared to the frictional effect of membrane viscosity is established by contrasting available data on the activation energy of ionic conductivity with that for membrane fluidity.
Abstract: Ion-carrier complexes and organic ions of similar size and shape have mobilities in lipid bilayer membranes which span several orders of magnitude. In this communication, an examination is made of the hypothesis that the basis for this unusually wide range of ionic mobilities is the potential energy barrier arising from image forces which selectively act on ions according to their polarizability. Using Poisson's equation to evaluate the electrostatic interaction between an ion and its surroundings, the potential energy barrier to ion transport due to image effects is computed, with the result that the potential energy barrier height depends strongly on ionic polarizability.
9 citations