Differentiated Transport Properties of Primary Cultured Distal Nephron
Distal nephron fragments were isolated by Percoll density centrifugation from collagenase-dispersed rabbit kidney cortex and grown on collagen-coated permeable supports. By 5 days, transmonolayer pd (Vtm) was 3.2 ± 0.7 mV (apical side negative) and transmonolayer conductance (Gtm) = 3.5 ± 0.4mS·cm-2. Incubation of monolayers in the presence of aldosterone increased transport of sodium and potassium as well as net acid secretion. This was accompanied by an increase in the amiloride-sensitive equivalent Isc and a decrease in Gtm· Fluorescence microscopy was used to estimate the proportion of intercalated cells in the monolayers. Carbonic-anhydrase-rich cells accounted for 46%, peanut-agglutinin-positive cells accounted for 24%. Solute concentration differences between apical and basolateral fluids were also measured. After 24 h incubation, the concentrations (mM; mean ± SEM) for apical versus basolateral solutions, respectively, were: Na+ 123.48 ± 2.33 vs. 150.25 ± 0.53; Cl- 113.75 ± 1.24 vs. 129.04 ± 1.28; K+ 7.58 ± 0.52 vs. 3.99 ± 0.02; total CO2 9.25 ± 0.49 vs. 21.33 ± 0.45; pH was 7.03 ± 0.03 vs. 7.36 ± 0.01. Aldosterone stimulated Na+ and K+ transport as well as H+ secretion. This was accompanied by an increase in both the amiloride-sensitive and insensitive components of the equivalent short-circuit current. We found that the type of culture medium determined the expression of transport properties. Growth of monolayers in different media increased Na+ and K+ transport and either stimulated or inhibited acid secretion. Our findings are consistent with the idea that these cultures display both electrical and transport properties characteristic of cortical collecting duct.