Renal tubules proximal convoluted, transport

Quigley R, Chakravarty S, Zhao X, Imig JD, Capdevila JH (2009) Increased renal proximal convoluted tubule transport contributes to hypertensionin Cyp4al4 knockout mice. Nephron Physiol 113 p23-28... 

In low-level chronic exposure, MX sequesters cadmium intracellularly as the cadmium-MT complex and thereby decreases the toxic effects of the metal. By contrast, extracellular cadmium-MX has been shown to be nephrotoxic to experimental animals. Parenteral injection of cadmium in the form of cadmium-MT can cause acute renal damage in rats and mice (Nordberg et al. 1975 Cherian et al. 1976 Squibb et al. 1984 Maitani et al. 1988). These toxic effects were similar to those observed after repeated exposure to cadmium salts but the critical renal concentration of cadmium is much lower after injection of cadmium-MX (10//g/g) than after repeated injections of cadmium salts (200//g/g). The low molecular weight cadmium-MX is freely filtered by the glomerulus and reabsorbed by the proximal convoluted tubules and can cause acute damage to the renal tubular epithelial cells (Cherian et al. 1976 Goyer et al. 1984 Dorian et al. 1992). It has been proposed that the hepatic cadmium-Mt is released and transported to kidney in blood plasma and that the nephrotoxicity occurs at a certain renal concentration of cadmium with chronic exposure (Goyer et al. 1978, 1984 Dudley et al. 1985). In a recent liver transplant experiment, the movement of cadmium-MX form liver to kidney was demonstrated in rats where the liver with cadmium-MX was transplanted to a control rat (Chan et al. 1993). 

Renal proximal tubular epithelium (e.g., convoluted tubules) reclaim protein, including immunoglobulin, from the urinary filtrate via sorting/recy-cling mechanisms in intracellular vesicles. The apical (lumen-facing) surface of these cells features a specialized brush border which expresses FcRn closely associated with (S2-microglobulin [110,116], Studies with cultured human renal proximal tubular epithelial cells have demonstrated bidirectional IgG transport and salvage by fully functional FcRn [110] as discussed further in the next section. 

Renal calcium transport Because the vertebrate organism is in constant need for calcium from the environment in order to maintain skeletal integrity, the calcium that is cleared from the circulation by glomerular filtration must be efficiently reabsorbed during the course of its passage along the renal tubular epithelium (for a review, Bushinsky 1999). The bulk of filtered calcium ( 70%) is reabsorbed in the proximal tubule, mainly on the paracel-lular route, while 20% is reabsorbed in the loop of Henle, where transcellular calcium transport - which is probably under the influence of PTH - becomes increasingly important. Reabsorption of 8% of filtered calcium occurs in the distal convoluted tubule, and involves transcellular transport that is activated by PTH and l,25(OH)2D3 (Bronner 1989). 

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