Loop diuretics increase calcium excretion and thiazides diuretics decrease calcium excretion

FUNCTION OF Na+ K+ 2Cl- channel

👉  Na K 2Cl channel at the thick ascending limb of loop of Henle is responsible for transport of  Na+, K+ and 2Cl- from intra-luminal to intra-cellular part of the loop of Henle.

👉K+ diffuses back into the lumen and Na+ is transported across the basolateral membrane to the ecf.

👉 Back diffusion of K+ into lumen creates a positive potential difference between the luminal (positive side) and basolateral (negativeside) membranes. 

👉 Positive potential difference drives reabsorption of Ca2+ and Mg2+  into the tubular capillaries.

MECHANISM OF INCREASED Ca+ EXCRETION BY LOOP DIURETICS

👉 Loop diuretics inhibit Na K 2Cl channel at the thick ascending limb of loop of henle.

👉  Reabsorption of Na K 2Cl does not occur

👉No development of positive potential difference.

👉No reabsorption of Ca2+

👉Increased excretion of Ca+

FUNCTION OF Na Cl SYMPORTER AT DISTAL TUBULE

👉 Reabsorption of only Na Cl. Therefore, unlike loop of Henle, there is no role of K+ back diffusion and therefore no question of positive potential difference.

👉 No potential difference driven Ca2+ reabsorption 

MECHANISM OF DECREASED Ca2+ EXCRETION BY THIAZIDE DIURETICS

👉  Inhibition of Na Cl symporter

👉 Decreased Na in tubular epithelial cells

👉 Compensatory increased functioning of Na+ Ca2+ exchanger at the basolateral membrane  to maintain  intracellular Na+.

👉 Decreased intracellular Ca in the epithelial cells.

👉 Increased reabsorption of Ca+ from luminal to intracellular side

👉Decreased Ca+ excretion in urine