Filtration in single isolated mammalian glomeruli

Abstract

We describe a new method for the study of ultrafiltration in single isolated glomeruli in vitro. Glomeruli without capsules were isolated by a sieving technique at room temperature in isotonic medium containing 4 to 6 g of bovine albumin per deciliter. The geometric volume of the glomeruli was reflected in the exchangeable tritiated water space; 70 to 75% of the water space was extracellular, most being intracapillary. When the protein concentration of the bath surrounding a single glomerulus was suddenly reduced, fluid entered the glomerular capillaries osmotically and they swelled. Subsequently, erythrocytes flowed out of the broken ends of the arterioles at the hilum. Individual erythrocytes could also be observed to move within capillary lumens. The rate of filtration of fluid into the capillary lumens was determined from optical measurements of total glomerular volume following a change in protein concentration of the external bathing medium. The filtration coefficient, K(f) was estimated from the initial slope of the relation between volume and time. The K(f) values for dogs, mature rabbits, immature rabbits, Buffalo rats, and Munich-Wistar rats were 17.03 ± 0.73, 5.57 ± 0.47, 3.70 ± 0.23, 5.97 ± 0.36, and 6.79 ± (SEM) 0.41 nl/min/mm Hg, respectively. The estimated K(f) values and the size of the glomeruli were proportional among species. These studies showed that the hydraulic conductivity of the capillary walls and the hydrodynamic properties of the capillary lumens can be determined in single isolated glomeruli. We suggest that this method may be applied to the study of physiologic and pathophysiologic processes in glomeruli of several species including man.