Altered Renal Expression of Na+ Transporters and ROMK in Protein-Deprived Rats

Abstract

Potassium depletion has been associated with altered sodium reabsorption in tubule segments. We studied if the altered abundance of Na⁺ transporters and ROMK are associated with distal potassium secretion that contributes to the development of hypokalemia in protein-deprived rats. After weaning, Wistar rats were fed with a low-protein diet (8%, LP) for 14 days and then recovered with a normal-protein (NP) diet (24%, RP). An age-matched control group was fed with an NP diet (24%, NP). We showed hypokalemia, lower glomerular filtration rate and higher FEK⁺ in the LP group. Immunoblotting revealed that the type 3 Na⁺/H⁺ exchanger in the cortex was decreased in the LP group. However, the type 2 Na⁺-K⁺-2Cl^– cotransporter was increased in the outer stripe of the outer medulla in the LP group. The abundance of the aldosterone-regulated Na⁺-Cl^– cotransporter (NCC) and epithelial Na⁺ channel (ENaC) was higher in the LP group and was associated with higher plasma aldosterone level. ROMK protein levels were increased. Na⁺/K⁺-ATPase protein levels were the same in both groups. After the recovery period, the expression of Na⁺ transporters and ROMK returned to control values. We conclude that increased expression of NCC, ENaC subunits, and ROMK contributed to distal potassium secretion leading to enhanced potassium excretion, which may explain the hypokalemia resulting from LP feeding. A role of aldosterone may be suggested.