title: The presumed potassium carrier Trk2p in Saccharomyces cerevisiae determines an H+-dependent, K+-independent current.
abstract: Ionic currents related to the major potassium uptake systems in Saccharomyces cerevisiae were examined by whole cell patch-clamping, under K+ replete conditions. Those currents have the following properties. They (1) are inward under all conditions investigated, (2) arise instantaneously with appropriate voltage steps, (3) depend solely upon the moderate affinity transporter Trk2p, not upon the high affinity transporter Trk1p. They (4) appear to be independent of the extracellular K+ concentration, (5) are also independent of extracellular Ca2+, Mg2+ and Cl- but (6) are strongly dependent on extracellular pH, being large at low pH (up to several hundred pA at -200 mV and pH 4) and near zero at high pH (above 7.5). They (7) increase in proportion to log[H+]o, rather than directly in proportion to the proton concentration and (8) behave kinetically as if each transporter cycle moved one proton plus one (high pH) or two (low pH) other ions, as yet unidentified. In view of background knowledge on K+ transport related to Trk2p, the new results suggest that the K+ status of yeast cells modulates both the kinetics of Trk2p-mediated transport and the identity of ions involved. That modulation could act either on the Trk2 protein itself or on interactions of Trk2 with other proteins in a hypothetical transporter complex. Structural considerations suggest a strong analogy to the KtrAB system in Vibrio alginolyticus and/or the TrkH system in Escherichia coli.
authors.affiliation: Department of Cellular and Molecular Physiology, Yale School of Medicine, New Haven, CT 06510, USA.
authors.forename: H
authors.initials: H
authors.lastname: Bihler
authors.forename: R F
authors.initials: RF
authors.lastname: Gaber
authors.forename: C L
authors.initials: CL
authors.lastname: Slayman
authors.forename: A
authors.initials: A
authors.lastname: Bertl
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D001692:Biological Transport; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D027682:Cation Transport Proteins; D002462:Cell Membrane / Q000378:metabolism*; D004553:Electric Conductivity; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism*; D017353:Gene Deletion; D006863:Hydrogen-Ion Concentration; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000378:metabolism*; D011522:Protons; D012441:Saccharomyces cerevisiae / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins
chemical_list: D002352:Carrier Proteins; D027682:Cation Transport Proteins; D005656:Fungal Proteins; D008565:Membrane Proteins; D011522:Protons; D029701:Saccharomyces cerevisiae Proteins; C085258:TRK2 protein, S cerevisiae; C068664:TRK1 protein, S cerevisiae; D000255:Adenosine Triphosphate; D011188:Potassium