HORMONAL-CONTROL OF RENAL MAGNESIUM HANDLING

In the kidney, the main site of magnesium transport is the thick ascen ding limb of Henle's loop which reabsorbs about 70% of filtered magnes ium. In the mouse and rat, this reabsorption takes place essentially i n the cortical portion of the thick ascending limb (cTAL). In the medu llary portion (mTAL) the transport is not significantly different from zero, irrespective of the voltage, whereas in the cTAL, it is exclusi vely 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 hormo ne-dependent increases in magnesium transport result from two synergis tic effects: (1) a rise in the transepithelial voltage and (2) an incr ease in the permeability to magnesium of the paracellular shunt pathwa y.