Overexpression of chloride channel CLC-K2 mRNA in the renal medulla of Dahl salt-sensitive rats

Objective The present study aimed to characterize the influence of salt intake on the gene expression of the kidney specific chloride channels CLC-K1 and CLC-K2 in the kidneys of salt-resistant and salt-sensitive Dahl rats. Design For this purpose Dahl salt-resistant (Dahl-R) and Dahl salt-sensitive rats (Dahl-S) were fed a low (0.02%), normal (0.6%) or high (4%) salt diet for 19 days and CLCK1 and -K2 mRNA expression was semiquantitated in cortex, outer and inner medulla. Methods Kidneys were macroscopically dissected, total RNA was isolated according to the guanidinium–thiocyanate–phenol-chloroform method and messenger RNAs for the kidney specific chloride channels CLC-K1 and CLC-K2 were measured by ribonuclease protection assay. Results Systolic blood pressure in high salt-treated Dahl-S rats increased to 204 ± 5 mmHg versus 150 ± 7 mmHg in Dahl-S controls. Dahl R and low salt Dahl-S rats showed no increase in blood pressure. For CLC-K1 mRNA we found an order of abundance inner medulla ≫ outer medulla ≫ cortex. There was no difference in mRNA abundance between Dahl-R and -S, nor any effect of the rate of salt intake on CLC-K1 mRNA abundance in the different kidney zones. CLC-K2 mRNA expression in cortex and outer medulla was similar between Dahl-R and -S rats. In the inner medulla, however, CLC-K2 mRNA was 1.7-fold higher in Dahl-S than in Dahl-R rats. In the cortex we found no influence of salt intake on CLC-K2 mRNA. In outer and inner medulla of Dahl-R rats and Dahl-S rats high salt diet led to a marked downregulation of CLC-K2 mRNA expression. Consequently, CLC-K2 gene expression in the inner medulla was 2.2-fold higher in Dahl-S than in Dahl-R rats in states of high salt diet. Conclusion Given that the CLC-K2 chloride channel in the outer and inner medulla contributes to salt reabsorption, our findings would suggest that Dahl-S rats have an increased medullary salt reabsorption. This may contribute to the inability of these animals to excrete an increased salt load at a normal renal perfusion pressure leading to the development of hypertension. J Hypertens 2000, 18:1289–1295 & Lippincott Williams & Wilkins.