Mammalian PIEZO channels rectify anionic currents

Under physiological conditions, mammalian PIEZO channels (PIEZO1 and PIEZO2) elicit transient currents mostly carried by monovalent and divalent cations. PIEZO1 is also known to permeate chloride ions, with a Cl ^- / Na ⁺ permeability ratio of about 0.2. Yet, little is known about how anions permeate PIEZO channels. Here, by separately measuring sodium and chloride currents using non-permanent counter-ions, we show that both PIEZO1 and PIEZO2 rectify chloride currents outwardly, favoring entry of chloride ions at voltages above their reversal potential, whereas little to no rectification was observed for sodium currents. Interestingly, chloride currents elicited by 9K, an anion-selective PIEZO1 mutant harboring multiple positive residues along intracellular pore fenestrations, also rectify but in the inward direction. Molecular dynamics simulation indicate that the inward rectification of chloride currents in 9K correlates with the largely positive electrostatic potential at the intracellular pore entrance, suggesting that rectification can be tuned by pore polarity. These results demonstrate that the pore of mammalian PIEZO channels inherently rectifies chloride currents.