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

Proximal tubular (PT) cells reabsorb most calcium (Ca²⁺ ), phosphate (PO₄ ^3- ), bicarbonate (HCO₃ ^- ), and oxalate (C₂ O₄ ^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 HCO₃ ^- , PO₄ ^3- , and C₂ O₄ ^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 HCO₃ ^- -induced currents in all PT cells, which was confirmed by using specific HCO₃ ^- channel inhibitor, S0859. Interestingly, such activities were diminished in PT cells from TRPC3^-/- mice, suggesting reduced HCO₃ ^- transport in absence of TRPC3. While PO₄ ^3- -induced currents were also concentration dependent in all PT cells (confirmed by PO₄ ^3- channel inhibitor, PF-06869206), those activities were reduced in absence of TRPC3, suggesting lower PO₄ ^3- reabsorption that can leave excess luminal PO₄ ^3- . Next, we applied thiosulfate (O₃ S₂ ^{2 -} ) as a competitive inhibitor of the SLC26a6 transporter upon C₂ O₄ ^2- current activation and observed a reduced C₂ O₄ ^2- -induced conductance which was greater in TRPC3^-/- PT cells. Together, these results suggest that the reduced activities of HCO₃ ^- , PO₄ ^3- , and C₂ O₄ ^2- transporters in moderately hypercalciuric (TRPC3^-/- ) PT cells can create a predisposing condition for CaP and CaP tubular crystallization, enabling CaP crystal formation in LOH of TRPC3^-/- mice.