Characteristics of the glomerular capillary membrane of the rat kidney as a hydrated gel. II. On the validity of the model

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Abstract
In our gel model applied to the glomerulus, maintenance of membrane integrity is assumed to be preserved not by rigid elements but by the electro-osmotic and balancing hydrostatic pressure offered by negative, fixed charges such that the membrane is able to withstand the external colloid osmotic and hydrostatic forces. Ir a previous study we used micropuncture data to estimate the charge densities required to fulfil this assumption. In the present study the validity of the model was examined from the transport of neutral and negative charged myoglobin as derived from their concentrations in renal venous blood. In order to determine the size of the pores, or rather meshes in the network, the venous concentration of [51Cr]EDTA was also analysed. Based on the ratio between EDTA and neutral myoglobin of 1.08 +/- 0.010 (mean +/- SE, n = 9), the equivalent pore radius was calculated to be approximately 40 A. The ratio of neutral to negative myoglobin in the two series performed was found to be 0.96 +/- 0.018 (n = 8) and 0.97 +/- 0.05 (n = 7), figures which were the same as ratio of 0.97 predicted on theoretical grounds. It is concluded that the experimental data support the hypotheses, although they may also be adapted to the transport in a homogeneously charged membrane; the charge density in this case was estimated at 2.3 mEq L-1. Assuming that the membrane constitutes a network with quadratic meshes, each fibre would seem to carry binding sites approximately 80 A apart and where, in between these binding sites, each fibre was calculated to carry three charges such that the mesh will thus be surrounded by 12 charges.

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