The molecular configuration of inulin: implications for ultrafiltration theory and glomerular permeability

A space-filling model of the inulin molecule, based solely on physico-chemical data in the literature, indicates that the gross shape of the solvated molecule is a cylinder having semi-length 25 A and radius 10 A. The axial dimensions of this model very nearly equal the equivalent estimates (25 and 10.5 A) previously determined by studying restricted passage of inulin through artificial membranes of known pore size (E. Middleton, J. Membrane Biol. 20:347, 1975). The good agreement between these independent in-vitro studies--neither of which depends on ultrafiltration theory--strongly suggests that glomerular pore size is considerably greater than predicted by the theory.