Maintaining K+ homeostasis is essential for the function of heart, skeletal muscles and neurons because
hypokalemia or hyperkalemia could cause life-threatening consequence such as cardiac arrhythmia. A
recent development in the field has firmly established the role of thiazide-sensitive Na-Cl cotransporter
(NCC) in the regulation of K+ homeostasis because the coordinated action among NCC, epithelial Na+
channel (ENaC) and ROMK is essential for maximally enhancing renal K+ excretion (EK) during high dietary
K+ intake (HK) and for effectively preventing K+ wasting during low dietary K+ intake (LK). The basolateral
Kir4.1 and Kir5.1 channels in the distal convoluted tubule (DCT) play an important role in controlling NCC
expression and activity. Our previous studies have demonstrated that HK induced inhibition of Kir4.1/Kir5.1
is an essential step for HK-induced inhibition of NCC. Conversely, LK-induced stimulation of Kir4.1/Kir5.1
of the DCT is an essential step for LK-induced stimulation of NCC. The mechanism by which the
basolateral Kir4.1/Kir5.1 in the DCT regulates NCC activity depends on Cl--sensitive with-no-lysine kinase
(WNK). The role of Kir4.1 and Kir5.1 in the regulation of renal K+ excretion has been demonstrated in the
mouse models: The deletion of Kir4.1 inhibits NCC activity and causes renal K+ wasting, whereas the
deletion of Kir5.1 increases NCC activity and reduces renal K+ excretion ability during HK intake. Thus,
Kir4.1 and Kir5.1 in the DCT serve as two important members of “potassium-sensor” mechanism. Although
the role of Kir4.1/Kir5.1 in regulating NCC and renal K+ excretion is well established, the regulatory
mechanism by which dietary K+ intake modulates Kir4.1 and Kir5.1 is not completely understood. We now
propose to examine the role of mechanistic target of rapamycin (mTOR) complex 1 (mTORc1) and mTOR
complex 2 (mTORc2) in mediating the effect of dietary K+ intake on Kir4.1/Kir5.1 of the DCT. We
hypothesize 1) Activation of mTORc1, partially via insulin-like-growth factor 1 (IGF-1), is critically
involved in mediating LK-intake-induced stimulation of Kir4.1/Kir5.1 of the DCT and NCC; 2)
Activation of mTORc2 inhibits Kir4.1/Kir5.1 by PKC during HK and is involved in HK-intake-induced
inhibition of NCC. The proposal has three specific Aims: 1)To test the hypothesis that mTORc1 regulates
Kir4.1/Kir5.1 of DCT and NCC under control conditions (normal K+) and plays a role in determining the
baseline renal K+ excretion; 2) To test the hypothesis that activation of IGF1-mTORc1 plays a key role in
mediating LK-induced stimulation of Kir4.1/Kir5.1 in the DCT and NCC and in suppressing renal K+
excretion; 3) Test the hypothesis that Activation of mTORc2 mediates HK-induced inhibition of Kir4.1/Kir5.1
via PKC and NCC in the DCT thereby enhancing ENaC-dependent renal EK. The significance of our
proposal is to explore the novel role of mTORc1/mTORc2 pathways in mediating effects of LK or HK on
Kir4.1/Kir5.1, NCC, ENaC and ROMK in the DCT and connecting tubule.