Regulations of Bicarbonate Ions in Pregnant Rat Kidney

Ma, Yang Rae; Lee, Song Eun; Cho, Hye Jung; Nam, Kwang IL; Bae, Choon Sang; Kim, Baik Yoon; Park, Sung Sik; Ahn, Kyu Youn

Abstract

The marked hemodynamic and hormonal changes of normal pregnancy are associated with striking alterations in renal physiology involving structure, dynamics, tubular function, and volume homeostasis. A number of acid-base or electrolyte disorders are associated with decreased or increased HCO3-reabsorption in the renal tubules. The present study was to examine the alterations of expression and distribution of Na+/HCO3-cotransporter (NBC), Na+/H+ exchanger-3 (NHE-3), and carbonic anhydrase I and II (CA I, II) proteins in the kidneys of non-pregnant (NP) and pregnant rats using Western blot analysis and immunohistochemistry. Sprague-Dawley female rats were studied on days 10 (P 10), 12 (P 12), 14 (P 14), 17 (P 17), and 19 (P 19) of pregnancy. Western blot analysis demonstrated that the expression of NBC, ~110 kDa at molecular mass, was increased in pregnant rats, particularly P 12, compared with NP rat. The expression of NHE-3, ~83 kDa at molecular mass, was increased in pregnant rats, particularly P 12 and P 14. The expression of CA I, ~30 kDa at molecular mass, was decreased in pregnant rats, particularly P 14, but, CA II protein, ~30 kDa at molecular mass, was similar NP rat. In immunohistochemistry, strong immunoreactivity of NBC of NP rat was exclusively detected in the basolateral membranes of S1 and S2 segment of proximal tubules whereas not in S3 segment. In pregnant rats, the pattern of cellular labeling of NBC was identical to that of NP rat, but signal intensity was increased, particularly P 12. In NHE-3, strong immunoreactivity was detected in apical membranes and brush borders of S3 segments and moderate in S1 and S2 segments. In pregnant rats, the pattern of cellular labeling was identical to that of NP rat, but the signal intensity was increased, particularly P 12 and P 14. Expression of CA I and II proteins was detected in entire collecting duct. Signal intensity was prominent in type A intercalated cells and moderate in type B intercalated cells. In pregnant rats, the pattern of cellular labeling of CA I and II proteins was identical to that of non-pregnant rat, but the signal intensity of CA I was decreased in cortical collecting duct, particularly P 14 and CA II was identical to that of NP rat. These results suggest that the regulation of NBC and NHE-3 expressions in the proximal tubules and CA I expression in cortical collecting duct may maintain HCO3-concentration during the pregnancy.