Single-nephron GFR and proximal-tubular Na⁺ reabsorption are altered in sgk1^–/– mice on a low-NaCl diet. (a) Schematic diagram of free-flow collection of tubular fluid from the last loop of the proximal tubule (PT) and the first loop of the distal tubule (DT) on the kidney surface in micropuncture experiments in anesthetized mice at day 3 after initiating a low-NaCl diet (0.15 g Na⁺/kg). (b) Fractional delivery of fluid and Na⁺ to proximal tubule and distal tubule as well as urine (n = 13–23 nephrons in 5–6 mice). *P < 0.05 versus sgk1^+/+ mice. (c) Correlation of Na⁺ reabsorption in proximal tubule with single-nephron filtration rate. Note that nephron filtration rate is reduced in sgk1^–/– mice and that for any given nephron filtration rate the Na⁺ reabsorption is higher in sgk1^–/– mice than in sgk1^+/+ mice, indicating a primary increase in proximal reabsorption in sgk1^–/– mice. Symbols are as given in Figure 2 legend.