Figure 1.
Pharmacological effects of Npt2a inhibition with PF-06869206 on renal and plasma parameters in mice with normal kidney function and 5/6 nephrectomy.
Eight weeks after subtotal nephrectomy (5/6 Nx) or sham surgery, inhibition of Npt2a by PF-06869206 (given via oral gavage, p.o.) caused a dose-dependent increase in urinary (A) Pi and (B) Ca2+ excretion (3 h metabolic cage experiments). This was associated with reductions in (C) plasma Pi and (D) PTH levels in sham and 5/6 Nx mice, while plasma Ca2+ remained unaffected (not shown). At a dose of 100 mg kg−1, effects on plasma Pi were smaller in magnitude in 5/6 Nx compared with sham mice; however, the effect on plasma PTH was not different between groups. In addition to the effect of PF-06869206 on urinary Pi and Ca2+ excretion, a dose-dependent increase in urinary Na+ excretion (E) was found in both groups, that was not significantly different from each other. Due to a lack of effect on urinary K+ excretion and unaffected natriuresis in Npt2a−/− mice (both not shown), we hypothesized that the natriuresis is a result of inhibition of Na+ transport in the connecting tubule/collecting duct, rather than in the proximal tubule, where the epithelial Na+ channel ENaC is expressed. In electrophysiological studies in acutely split-open cortical collecting ducts of C57BL/6 mice, ENaC open probability was measured in cell-attached patches formed on the apical membrane of principal cells. The pipette was backfilled with Npt2a inhibitor (30 µmol L−1). A continuous current trace is shown in (F). The areas under the bars over the continuous traces are shown below at expanded timescales. Dashed lines indicate the respective current levels, with c denoting the closed state and o denoting the open state. Open probability was acutely inhibited (∼85%) by PF-06869206, providing evidence that the natriuresis might be the consequence of off-target effects on ENaC. Data taken from [8,45]. *P < 0.05 versus vehicle, §P < 0.05 versus sham, #P < 0.05 versus previous time point.