Cellular Mechanisms of Renal Calcium Transport

About 60% of filtered calcium is reabsorbed within the proximal convoluted tubule (Fig. 1). In the beginning of the proximal tubule (first millimeter) net calcium reabsorption lags behind net fluid reabsorption and tubular fluid calcium concentration (TF) is found to exceed that in ultrafiltrate (UF) by 10–20%. Accordingly, the ratio TF/UF approaches 1.1–1.2. In later portions of the proximal tubule calcium reabsorption parallels fluid reabsorption and TF/UF remains constant [1, 14, 17–19, 32, 46, 50, 53].