Magnesium Handling in the Nephron

Question 1

how much magnesium is bound to protein?

Answer 1

30%

Question 2

what’s the mechanism of proximal tubular reabsorption?

Answer 2

Paracellular reabsorption, just like Ca, except that only 15% of Mg reabsorption happens here

Question 3

what’s the main regulator of Mg reabsorption in the PCT?

Answer 3

volume, expanded volume increases excretion

Question 4

what’s the mechanism of reabsorption in the TAL?

Answer 4

the electrical gradient established by the NKCC/ROMK channels & Na backleak helps to drive paracellular reabsorption

Question 5

how much Mg reabsorption happens in the TAL?

Answer 5

70%

Question 6

how is TAL reabsorption regulated?

Answer 6

by the divalent cation regulator, heretofore known as the CaSR, which blocks the ROMK channel via the action of the 20-HETE

Question 7

how is sodium backleak into the lumen created?

Answer 7

Claudin-16 allows the passage of Na back through the lumen, as the concentration of luminal Na falls, while Claudin-19 blocks Cl from following

Question 8

what’s the mechanism of the DCT reabsorption of Mg?

Answer 8

transcellularly via the action of the TRPM6 & 7

Question 9

how much Mg is reabsorbed in the DCT

Answer 9

10%

Question 10

How does Gitelman’s syndrome affect Mg transport?

Answer 10

it lowers the expression of TRPM6

Question 11

what’s the intermediate for isolated recessive hypomagnesemia (Gitelman’s)

Answer 11

a homozygous inactivating mutation in pro-EGF (epithelial growth factor) causes an inactivating effect on the EGF receptor which inactivates the TRPM6 receptor (via a mechanism that isn’t understood)

Question 12

what drug causes hypomagenesmia?

Answer 12

cetuximab: EGFR inhibitor; causes facial rash