Tandem upregulation of ion transporters in thick ascending limb of Henle's loop of young Milan hypertensive strain of rats.

Introduction: Milan hypertensive strain (MHS) of rat represents as one of the ideal rat models to study the genetic form of hypertension associated with aberrant renal salt reabsorption. In contrast to Milan normotensive strain (MNS), MHS rats possess missense mutations in three adducin genes and develop hypertension at 3 months old due to upregulation of sodium-chloride cotransporter (NCC). At pre-hypertensive stage (23-25 days old), MHS rats show enhanced protein abundance of Na+-K+-2Cl- cotransporter (NKCC2) but retain blood pressure comparable to MNS probably through enhanced GFR and reduced NCC and α-subunit of epithelial sodium channel (α-ENaC) expressed in distal convoluted tubule (DCT) and collecting duct (CD).

Methods: In the present study, mRNA and protein expressions of ion transporters in thick ascending limb of Henle's loop (TAL) of young MHS rats were investigated.

Results: Protein abundance of core-glycosylated form of renal outer medullary potassium channel (ROMK) in inner stripe of outer medulla (ISOM) is remarkably increased in MHS rats at prehypertensive stage. Furthermore, basolaterally expressed Na+-K+-ATPase and Barttin were upregulated.

Discussion/conclusion: These results may indicate that in TAL of MHS rats at this age, both total NKCC2 and core-glycosylated ROMK are upregulated in tandem potentially to balance the luminal potassium concentration. On the basolateral side, upregulation of Na+-K+-ATPase and CLC-Ka/b may energize the excretion of sodium and chloride out from the cells. These data may suggest the interplay of apical and basolateral ion transporters in TAL for the modulation of TAL function in favor of enhancing the transepithelial sodium reabsorption, although this seems compensated by NCC and ENaC expressed at the downstream nephron segments in young MHS rats.