pH-regulated nonelectrogenic anion transport by phenylthiosemicarbazones

摘要

Gated ion transport across biological membrane is an intrinsic process regulated by protein channels. Synthetic anion carriers (anionophores) have potential applications in biological research, however, previous reported examples are mostly nonspecific, capable of mediating both electrogenic and electroneutral (non-electrogenic) transport processes. Here, we show the transmembrane Cl? transport studies of synthetic phenylthiosemicarbazones mimicking the function of acid-sensing (proton-gated) ion channels. These anionophores have remarkable pH-switchable transport properties with up to 640-fold increase in transport efficacy on going from pH 7.2 to 4.0. This “gated” process is triggered by protonation of the imino nitrogen and concomitant conformational change of the anion binding thiourea moiety from anti to syn. By using a combination of two cationophore-coupled transport assays, with either monensin or valinomycin, we have elucidated the fundamental transport mechanism of phenylthiosemicarbazones which is shown to be non-electrogenic, inseparable H+/Cl? cotransport. This study demonstrates the first examples of pH-switchable non-electrogenic anion transporters