Ablation of TRPC3 compromises bicarbonate and phosphate transporter activity in mice proximal tubular cells.

Proximal tubular (PT) cells reabsorb most calcium (Ca 2+ ), phosphate (PO 4 3- ), bicarbonate (HCO 3 - ), and oxalate (C 2 O 4 2- ) ions. We have shown that mice lacking Transient Receptor Potential Canonical 3 (TRPC3-/-) channel are moderately hypercalciuric with presentation of luminal calcium phosphate (CaP) crystals at the loop of Henle (LOH). However, other predisposing factors for such crystal deposition are unknown. Thus, we examined the distinctions in functional status of HCO 3 - , PO 4 3- , and C 2 O 4 2- transporters in PT cells of wild type (WT) and TRPC3-/- mice by whole-cell patch clamp techniques to assess their contribution in the development of LOH CaP crystals. Here we show the development of concentration-dependent HCO 3 - -induced currents in all PT cells, which was confirmed by using specific HCO 3 - channel inhibitor, S0859. Interestingly, such activities were diminished in PT cells from TRPC3-/- mice, suggesting reduced HCO 3 - transport in absence of TRPC3. While PO 4 3- -induced currents were also concentration-dependent in all PT cells (confirmed by PO 4 3- channel inhibitor, PF-06869206), those activities were reduced in absence of TRPC3, suggesting lower PO 4 3- reabsorption that can leave excess luminal PO 4 3- . Next, we applied thiosulfate (O 3 S 2 -2 ) as a competitive inhibitor of the SLC26a6 transporter upon C 2 O 4 2- current activation and observed a reduced C 2 O 4 2- -induced conductance which was greater in TRPC3-/- PT cells. Together, these results suggest that the reduced activities of HCO 3 - , PO 4 3- , and C 2 O 4 2- transporters in moderately hypercalciuric (TRPC3-/-) PT cells can create a predisposing condition for CaP and CaP+CaOx tubular crystallization, enabling CaP crystal formation in LOH of TRPC3-/- mice.