Permeability to magnesium is low in the proximal straight, and probably convoluted, tubule. The thin descending and ascending limbs have not been studied. The cortical thick ascending limb transports magnesium in a voltage-dependent way similar to calcium. PTH and dibutyryl cAMP uncover active transport in the cortical thick ascending limb, which has a basal absorptive rate of 0.8 to 0.9 pEq/mm.min. The distal convoluted tubule and connecting tubule have not been studied. The cortical collecting tubule has no significant net transport, and there is no effect of PTH to enhance transport.
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