Ectopic Potassium Uptake in trk1 trk2 Mutants ofSaccharomyces cerevisiae Correlates with a Highly Hyperpolarized Membrane Potential

Abstract

Null trk1 trk2 mutants of Saccharomyces cerevisiae exhibit a low-affinity uptake of K ؉ and Rb ؉ . We show that this low-affinity Rb ؉ uptake is mediated by several independent transporters, and that trk1⌬ cells and especially trk1⌬ trk2⌬ cells are highly hyperpolarized. Differences in the membrane potentials were assessed for sensitivity to hygromycin B and by flow cytometric analyses of cellular DiOC 6 (3) fluorescence. On the basis of the latter analyses, it is proposed that Trk1p and Trk2p are involved in the control of the membrane potential, preventing excessive hyperpolarizations. K ؉ starvation and nitrogen starvation hyperpolarize both TRK1 TRK2 and trk1⌬ trk2⌬ cells, thus suggesting that other proteins, in addition to Trk1p and Trk2p, participate in the control of the membrane potential. The HAK1 K ؉ transporter from Schwanniomyces occidentalis suppresses the K ؉ -defective transport of trk1⌬ trk2⌬ cells but not the high hyperpolarization, and the HKT1 K ؉ transporter from wheat suppresses both defects, in the presence of Na ؉ . We discuss the mechanism involved in the control of the membrane potential by Trk1p and Trk2p and the causal relationship between the high membrane potential (negative inside) of trk1⌬ trk2⌬ cells and its ectopic transport of alkali cations.

Saccharomyces cerevisiae Multidrug Resistance Transporter Qdr2 Is Implicated in Potassium Uptake, Providing a Physiological Advantage to Quinidine-Stressed Cells

“…However, the viability of ⌬trk1 ⌬trk2 cells has revealed the existence of additional forms to transport potassium. Although the nature of this transport remains unclear, the activities of a nonselective cation channel and different nonspecific transporters have been postulated (3,23,38,50). Here, we provide evidence suggesting that Qdr2p may be one of these predicted low-affinity uptake systems for K ϩ .…”

“…However, the nature of this transport remains to be elucidated, although the nonspecific uptake of potassium occurring through sugar and amino acid permeases has been postulated (22,23,50). Based on a number of evidences, Wright et al (50) have considered that amino acid:H ϩ symporters may not have an absolute requirement for H ϩ as a cosubstrate and may be capable of coupling K ϩ ions to drive amino acid uptake.…”

Reconstitution in yeast of the Arabidopsis SOS signaling pathway for Na + homeostasis

“…Saccharomyces cerevisiae strains W⌬3 (⌬trk1::LEU2, ⌬trk2::HIS3), G19 (⌬ena1::HIS3::ena4), and ANT3 (⌬ena1::HIS3::ena4, ⌬nha1::LEU2) have been described (8,9). AXT3K (⌬ena1::HIS3::ena4, ⌬nha1::LEU2, ⌬nhx1::KanMX4) was constructed from ANT3 by replacement of the EcoRI͞PstI fragment internal to NHX1 with an EcoRI͞PstI fragment containing the selection marker KanMX.…”

The TRK1 Potassium Transporter Is the Critical Effector for Killing of Candida albicans by the Cationic Protein, Histatin 5

“…Another protein involved in these potassium-related phenomena is the major K ϩ uptake system in Candida, Trk1p. This transporter, initially cloned in Saccharomyces by Gaber et al (29), is believed to operate as a proton-coupled system, having similar properties to the high affinity K ϩ uptake system in Neurospora (30,31), and has also been reckoned as a voltage regulator on the basis of dye distribution measurements (32). Finally, it has recently been shown to mediate chloride currents through Saccharomyces plasma membrane, which are made easily visible by raising intracellular Cl Ϫ above ϳ10 mM (33).…”