Paraoxonase 3 regulates the pore-forming α subunit of the large-conductance K⁺ channel

Paraoxonase 3 (PON3) is expressed in the aldosterone-sensitive distal nephron (ASDN) where the fine tuning of Na⁺ and K⁺ homeostasis in the kidney occurs. Flow-induced K⁺ secretion within intercalated cells (ICs) of the ASDN is mediated by the large-conductance K⁺ (BK) channels. We have previously shown that renal PON3 expression was altered by dietary K⁺ intake and that Pon3 knockout (KO) mice had lower plasma [K⁺]. These findings led us to hypothesize that PON3 may have a role in regulating renal K⁺ secretion by altering BK channel functional expression. The present study shows that both PON3 and the pore-forming α subunit of the BK channel (αBK) are expressed in ICs of mouse kidney and that the two proteins co-localize to the same cellular compartments when expressed in HEK293 cells. Using a biochemical approach, we show that PON3 interacts with αBK endogenously in the mouse kidney and when both proteins were co-expressed in HEK293 cells. We also examined the effects of PON3 on αBK expression and channel activity in HEK293 cells. We found that paxilline-sensitive BK currents were significantly reduced by PON3 expression, likely a consequence of lower surface abundance of αBK. Consistent with this finding, we observed a stronger αBK staining signal in ICs of Pon3 KO kidneys. Together, our data suggest that PON3 negatively regulates the functional expression of BK channels.