A 56-year-old man with severe hypertension is started on a medication that inhibits the Na+-K+-2Cl- symporter in the thick ascending limb of the loop…

Loop diuretics inhibit the Na+-K+-2Cl- cotransporter in the thick ascending limb. Because potassium is recycled back into the lumen via ROMK channels, it creates a lumen-positive electrical potential. This positive potential is the driving force for paracellular reabsorption of divalent cations like $Ca^{2+}$ and $Mg^{2+}$. Blocking this transporter abolishes the lumen-positive potential, causing hypocalcemia and hypomagnesemia.