A novel low-affinity H+-Cl- co-transporter in yeast: characterization by patch clamp

We have used the patch clamp technique to characterize a novel low affinity H + coupled Cl - transporter in the plasma membrane of Saccharomyces cerevisiae. Cl - -induced inward currents were observed upon the addition of millimolar concentrations of extracellular Cl - . These currents were independent of the cation species present but were dependent on the membrane voltage and the extracellular pH such that Cl - -induced inward currents were reduced as pH was increased from 5.5 to 8.0. These data are consistent with an electrogenic co-transport of nH + and Cl - where n > 1. In accord with the results from patch clamp experiments, Cl - uptake into intact yeast cells was pH-dependent with an apparent K m of 93 mM. Furthermore, Cl - uptake was up-regulated by pre-incubation in elevated extracellular NaCl concentrations, but was insensitive to a pre-incubation in sorbitol. A possible role for the nH + /Cl - symport in equimolar osmoregulation during salt stress is discussed.