Characteristics of the glomerular capillary membrane of the rat kidney as a hydrated gel. I. Hypothetical structure.

It is suggested that the glomerular capillary membrane constitutes a flexible gel, where negative charges fixed to the matrix of the membrane account for the maintenance of its integrity. In this model, the hydrostatic pressure throughout the membrane is assumed to equal the glomerular capillary pressure. Pglom. of 56.7 mmHg. On the plasma side of the membrane, the charge-induced electro-osmotic pressure therefore has to balance the colloid osmotic pressure of glomerular plasma, and on its Bowman's space side, it has to balance the pressure drop. Pglom-PBow, across this interphase. Using micropuncture technique, the glomerular plasma colloid osmotic pressure of 20.6 mmHg was found to require a charge density of 24.8 mEq L-1 and the pressure drop at the Bowman's space side of 56.7-12.2 = 44.5 mmHg a density of 36.6 mEq L-1. The transmembranous electric potential difference was estimated at -1.1 mV. a potential which, in a negatively charge membrane, will also constitute the net driving force for the fluid transfer; this force will be close to, but not identical with, that calculated as conventional from the Starling forces of, in the present case, 23.9 mmHg.61 In the present analysis the distribution of charges in the fluid of the pore resulting from charged groups fixed to the rim of the pore is also considered.