Abstract
We studied gender differences in Na(+)-Cl(-) cotransporter (NCC) activity and expression in wild-type (WT) and AT(1a) receptor knockout (KO) mice. In renal clearance experiments, urine volume (UV), glomerular filtration rate, absolute Na(+) (E(Na)) and K(+) (E(K)), and fractional Na(+) (FE(Na)) and K(+) excretion were measured and compared at peak changes after bolus intravenous injection of hydrochlorothiazide (HCTZ; 30 mg/kg). In WT, females responded more strongly than males to HCTZ, with larger fractional increases of UV (7.8- vs. 3.4-fold), E(Na) (11.7- vs. 5.7-fold), FE(Na) (7.9- vs. 4.9-fold), and E(K) (2.8- vs. 1.4-fold). In contrast, there were no gender differences in the responses to the diuretic in KO mice; HCTZ produced greater effects on male KO than on WT but similar effects on females. In WT, total (tNCC) and phosphorylated (pNCC) NCC protein expressions were 1.8- and 4.6-fold higher in females compared with males (P < 0.05), consistent with the larger response to HCTZ. In KO mice, tNCC and pNCC increased significantly in males to levels not different from those in females. There were no gender differences in the expression of the Na(+)/H(+) exchanger (NHE3) in WT; NHE3 protein decreased to similar extents in male and female KO animals, suggesting AT(1a)-mediated NHE3 expression in proximal tubules. The resulting increase in delivery of NaCl to the distal nephron may underlie increased NCC expression and activity in mice lacking the AT(1a) receptor.