Effects of volume depletion and NAHCO3 loading on the expression of NA+/H+ exchanger isoform 3, NA+: HCO3- cotransporter type 1 and nitric oxide synthase in rat kidney

1. The effects of volume depletion and NaHCO3 loading on the expression of Na+/H+ exchanger isoform 3 (NHE3), Na+: HCO3- cotransporter type I (NBC1) and neuronal (n) and inducible (i) isoforms of nitric oxide synthase (NOS) were determined in rat kidney. 2. Adult male Sprague-Dawley rats were used. Rats were divided into four groups: (i) euvolaemic (EC); (ii) hypovolaemic (HC); (iii) euvolaemia with NaHCO3 loading (EB); and (iv) hypovolaemia with NaHCO3 loading (HB). The expression of NHE3, NBC1, nNOS and iNOS proteins was determined in the cortex of the kidney by immunoblotting and immunohistochemistry. Tissue content of nitric oxide (NO) metabolites (NOx) were also determined in the cortex using a colourimetric assay. 3. Compared with the EC group, the expression of NHE3 and NBC1 was increased in the HC group and decreased in the EB group. Comparing the EB and HB groups, the expression of NHE3 and NBC1 was higher in the latter group. The expression of NHE3 was decreased and that of NBC1 was increased in the HB group compared with the HC group. The NO, content and nNOS expression were decreased in the hypovolaemic (HC) and NaHCO3-loaded (EB and HB) rats. Moreover, the expression of NOS was decreased in the HB group compared with the other groups. 4. An altered volume status and NaHCO3 loading may affect the regulation of NHE3 and NBC1 in the kidney and the endogenous NO system may play a role in the observed effects.