mTORc2 Stimulates Renal Potassium (K+) Excretion During Overnight-High-K+ by Simultaneously Stimulating Epithelial Sodium Channel (ENaC)/Potassium Kir1.1 Channel (ROMK) and Inhibiting Kir4.1/Kir5.1

Background: The mTORc2 is a multiprotein complex and RICTOR (rapamycin insensitive companion of mTOR) is one of the core components of mTORc2. Previous studies have demonstrated the role of mTORc2 in regulating renal K+ -excretion by modulating Kir4.1/Kir5.1 in the distal convoluted tubule (DCT), regulating ENaC and ROMK in the collecting duct. The aim of the study is to examine whether overnight-high-K+-intake-induced stimulation of renal K+-excretion is achieved by simultaneous initiation of mTORc2 -dependent inhibition of Kir4.1/Kir5.1 in the DCT and mTORc2-dependent stimulation of ENaC and ROMK in the late distal tubules. Methods: We performed patch-clamp experiments, immunoblotting, metabolic cage and in vivo measurement of urinary-K+-excretion in kidney-tubule-specific RICTOR (Rapamycin-insensitive-companion of mTOR) knockout mice (Ks-RICTOR-KO) and corresponding wild-type mice (Rictorflox/flox). Results: Ks-RICTOR-KO mice had a lower urinary K+-excretion and higher plasma K+ concentration than Rictorflox/flox mice. Moreover, overnight high-K+ intake further increased plasma K+ level in Ks-RICTOR-KO mice but not in Rictorflox/flox mice. Ks-RICTOR-KO mice had higher basolateral Kir4.1/Kir5.1 activity in the DCT than Rictorflox/flox mice. In contrast, amiloride-sensitive Na+-currents (ENaC) and tertiapin-Q (TPNQ)-sensitive-K+-currents (ROMK) were lower in both late-DCT/early-connecting-tubule (CNT) and cortical- collecting-duct (CCD) of Ks-RICTOR-KO mice than Rictorflox/flox mice. Overnight high-K+ intake decreased Kir4.1/Kir5.1 activity of DCT and increased amiloride-sensitive Na+-currents and TPNQ-sensitive K+ currents in late-DCT/early-CNT and in the CCD in Rictorflox/flox mice. However, these effects of overnight-high-K+ were absent in Ks-RICTOR-KO mice. Finally, in vivo measurement-of-urinary-K+- excretion showed that urinary K+-excretion in Ks-RICTOR-KO mice on overnight-high-K was lower than Rictorflox/flox mice. Conclusion: The mTORc2 plays a role in maintaining baseline-activity of Kir4.1/Kir5.1, ROMK and ENaC. It mediates the effect of high-K+-intake on ENaC and ROMK not only in the CCD but also in late-DCT/early-CNT. The mTORc2 plays a key role in stimulating renal K+ excretion during high-K+-loading by simultaneously inhibiting Kir4.1/Kir5.1 and stimulating ENaC and ROMK. Funding: NIDDK Support