Hormonal control of renal magnesium handling.

In the kidney, the main site of magnesium transport is the thick ascending limb of Henle's loop which reabsorbs about 70% of filtered magnesium. In the mouse and rat, this reabsorption takes place essentially in the cortical portion of the thick ascending limb (cTAL). In the medullary portion (mTAL) the transport is not significantly different from zero, irrespective of the voltage, whereas in the cTAL, it is exclusively voltage-dependent. In the cTAL, up to six hormones (including PTH) or agonists can stimulate Mg transport. They are totally inactive in the mTAL. The data obtained in the mouse cTAL indicate that the hormone-dependent increases in magnesium transport result from two synergistic effects: (1) a rise in the transepithelial voltage and (2) an increase in the permeability to magnesium of the paracellular shunt pathway.