Abstract P244: Tubular Sites Of Mtorc2 Inhibition Of Sodium Transport In Dahl Salt-sensitive Rats.

Abstract

Background: There is evidence that the mTOR signaling pathway plays an important role in salt induced hypertension in the Dahl salt-sensitive (SS) rat via regulation of Na + excretion. PP242 inhibition of mTORC1-2 prevented hypertension in SS rats and intrarenal PP242 produced a 4-fold increase of Na + excretion while selective inhibition of mTORC1 with rapamycin had no effect. The goal of the present study was to identify the renal tubular Na + transporters regulated by the mTORC2 pathway. Methods: Natriuretic effectors of mTORC2 were deduced from the differences of Na + excreted with PP242 treatment beyond that observed by the natriuretic actions of benzamil (B; ENaC inhibitor), furosemide (F; NKCC2 inhibitor), hydrochlorothiazide (H; NCC inhibitor) and in combination (B+F+H). Unanesthetized SS rats were first administered B, F, H or B+F+H (i.p.) and 2 days later with co-administration of PP242 with these same reagents. Rats were studied when fed 0.4% NaCl (LS) and then following 3 weeks of a 4.0% NaCl (HS) diet. The effect of PP242 on ENaC activity in freshly isolated cortical collecting ducts was also examined using cell-attached patch clamp electrophysiology. Results: Urine Na + excretion rates determined at 20 min. intervals over 80 minutes increased nearly 2-fold with administration of PP242 + B, compared to B alone [0.10 + 0.02 vs. 0.04 + 0.01 mmol/100gbw (n=8; P<0.05)] and similarly in the F and H comparisons [F: 0.20 + 0.02 vs. 0.10 + 0.02 mmol/100gbw (n=8; P<0.05); H: 0.05 + 0.01 vs. 0.03 + 0.01 mmol/100gbw (n=8; P=0.06)]. PP242 given in the presence of F+B+H did not further enhance the overall natriuretic response. Rats fed HS showed little enhancement of natriuresis when PP242 was administered with any of the drugs. Minimum changes in K + excretion were observed with PP242 in LS or HS studies. Patch clamp studies found that PP242 reduced ENaC activity through reduction of the open channel probability (Po) in both LS and HS fed rats. Western blot data indicated that PP242 reduced pNCC T53 and phosphorylation of SGK1. Conclusion: Together, these studies found evidence that the natriuretic actions of PP242 are a consequence of inhibitory actions on the ENaC and NCC transporters in the distal nephron segments.