mTORc2 in Distal-Convoluted-Tubule and Renal K+-Excretion during High Dietary K+ Intake.

BACKGROUND

Renal mTORc2 plays a role in regulating renal K+-excretion (renal-EK) and K+-homeostasis. Inhibition of renal mTORc2 caused hyperkalemia due to suppressing epithelial-Na+-channel (ENaC) and ROMK (Kir1.1) in the collecting duct. We now explore whether mTORc2 of DCT regulates basolateral Kir4.1/Kir5.1, NCC and renal-EK.

METHODS

We used patch-clamp-technique to examine basolateral Kir4.1/Kir5.1 in early-DCT, immunoblotting and immunofluorescence to examine NCC expression and in vivo measurement of urinary K+-excretion to determine baseline renal-EK in the mice treated with mTORc2-inhibitor and in DCT-specific Rapamycin-Insensitive-Companion- of-mTOR knockout (DCT-RICTOR-KO) mice.

RESULTS

Inhibition of mTORc2 with AZD8055 abolished high-K+-induced inhibition of Kir4.1/Kir5.1 in DCT, high-K+-induced depolarization of DCT membrane and high-K+-induced suppression of pNCC expression. AZD8055 stimulated the 40-pS-inwardly-rectifying-K+ channel (Kir4.1/Kir5.1-heterotetramer) in early-DCT in the mice on overnight-high-K+, this effect was absent in the presence of PKC-inhibitor which also stimulated Kir4.1/Kir5.1. AZD8055-treatment decreased renal-EK in animals on overnight-high-K+. Deletion of RICTOR in the DCT increased the Kir4.1/Kir5.1-mediated K+-currents, hyperpolarized DCT membrane and increased the expression of pWNK4 and pNCC. Renal-EK was lower and plasma-K+ was higher in DCT-RICTOR-KO mice than corresponding control mice. Also, overnight-high-K+ did not inhibit Kir4.1/Kir5.1 activity in the DCT and failed to inhibit the expression of pNCC in DCT-RICTOR-KO mice. Overnight-high-K+ stimulated renal-EK in control mice, but this effect was attenuated in DCT-RICTOR-KO mice. Thus, overnight-high-K+ induced hyperkalemia in DCT-RICTOR-KO mice but not in control mice.

CONCLUSIONS

mTORc2 of the DCT inhibits Kir4.1/Kir5.1 activity and NCC expression, and stimulates renal-EK during high-K+-intake.

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