CHARACTERISTICS OF THE GLOMERULAR CAPILLARY MEMBRANE OF THE RAT-KIDNEY AS A HYDRATED GEL .1. HYPOTHETICAL STRUCTURE

It is suggested that the glomerular capillary membrane constitutes a f lexible gel. where negative charges fixed to the matrix of the membran e account for the maintenance of its integrity. In this model. the hyd rostatic pressure throughout the membrane is assumed to equal the glom erular capillary pressure. P-glom, of 56.7 mmHg. On the plasma side of the membrane, the charge-induced electro-osmotic pressure therefore h as to balance the colloid osmotic pressure of glomerular plasma, and o n its Bowman's space side. it has to balance the pressure drop. P-glom -P-Bow, across this interphase. Using micropuncture technique. the glo merular plasma colloid osmotic pressure of 20.6 mmHg was found to requ ire a charge density of 24.8 mEq L(-1) and the pressure drop at the Bo wman'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 al - 1.1 mV, a potential which, in a negatively charge membrane, will also constitute the net driving force for the fluid transfer: this force wi ll be close to, but not identical with, that calculated as conventiona l from the Starling forces of, in the present case. 23.9 mmHg. 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 con sidered.