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 cerevis iae. Cl--induced inward currents were observed upon the addition of millimo lar 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 electro genic 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-de pendent with an apparent K-m of 93 mM. Furthermore, Cl- uptake was up-regul ated by pre-incubation in elevated extracellular NaCl concentrations, but w as insensitive to a pre-incubation in sorbitol. A possible role for the nH( +)/Cl- symport in equimolar osmoregulation during salt stress is discussed.