Steric hindrances in protein permeation through the basement membrane studied in acellular kidney

Acellular kidney preparations were used for studying the steric hindrances in the glomerular basement barrier. In accordance with the reports of other authors our data have provided evidence that, in this model the basement membrane does not suffer from gross ruptures and also preserves its integrity with regard to the proteoglycan moiety. Detergent treatment of the passing protein solution (used for the removal of cellular elements) results in abolishing charge differences. Under such conditions the molar percentage of proteins passing through the GBM barrier is inversely proportional to the logarithm of relative molecular mass. Application of different detergents in preparing the acellular kidney (Triton X-100 and sarcosyl) and in the treatment of individual proteins under study leads to linear relationships of different slopes which is ascribed to the differences in electrostatic repulsive forces introduced by the detergent. The proportion of molecules passing through the GBM barrier increases with increasing protein concentration in the perfusate approaching a limiting value at very high concentrations (0.1 mmol/l). This indicates that the individual protein molecules compete for the free space in basement membrane channels, a conclusion further supported by the fact that permeation of a protein through the barrier can be effectively blocked by increasing the overall protein concentration in the perfusate with another protein species.