In PCT, sodium reabsorption is prevented by:

Osmotic diuretics act primarily in the proximal tubule as non resorbable solutes that limit the osmosis of water into the interstitial space and thereby reduce luminal Na+ concentration to the point that net Na+ reabsorption ceases. Note: Although early micropuncture studies suppoed this concept, subsequent studies suggested that this mechanism, while operative, may be of only secondary impoance and that the major site of action of osmotic diuretics is the loop of Henle. Also Know: Ethacrynic acid is an inhibitor of Na+-K+-2Cl- sympo act primarily in the thick ascending limb. Triamterene is an inhibitor of renal epithelial Na+ channels(K+ sparing diuretic.) Acetazolamide are inhibitors of carbonic anhydrase. Ref: Reilly R.F., Jackson E.K. (2011). Chapter 25. Regulation of Renal Function and Vascular Volume. In L.L. Brunton, B.A. Chabner, B.C. Knollmann (Eds),Goodman & Gilman's The Pharmacological Basis of Therapeutics, 12e.