Prestin is a member of the SLC26A family and acts as a piezoelectric transducer that mediates fast electromotility, i. e. fast voltage-dependent length changes, in mammalian outer hair cells (OHC). In OHCs prestin resides in the lateral cell membrane and is the elementary molecular motor of the cochlear amplifier, but little is known about structural and molecular details of this motor function. Nonmammalian SLC26A5 orthologs show no electromotility but act as a divalent/monovalent anion exchanger. Schaechinger et al. (2007) showed that zebrafish and chicken prestin exchange oxalate and/or sulfate for chloride in a strictly coupled manner with a 1:1 stoichiometry. A chimeric engineered prestin revealed that prestin transports anions by an alternate access cycle followed by an anion-dependent transition generating electromotility. This suggests that the electromechanical process evolved from an ancestral transport mechanism.

Using patch clamp recordings from transiently transfected CHO cells, we demonstrate thatCiona intestinalisprestin (CiPres) acts as divalent/monovalent anion exchanger. CiPres exchanged oxalate or sulfate for chloride in an electrogenic manner and this transport was reversibly blocked by salicylate. Furthermore, we identified electrogenic antiport of bicarbonate against oxalate. The mutation of a highly conserved glutamate among the SLC26 family at position 419 in CiPres abolished all modes of coupled transport. Moreover, we demonstrate that CiPres exhibits an uncoupled transport activity for thiocyanate and nitrate. Thus anion transport of non-mammalian prestin closely resembles the transport characteristics of the mammalian anion transporters SLC26A3 and SLC26A6 (Ohana 2011).