Conservation and dispersion of sequence and function in fungal TRK potassium transporters: focus on Candida albicans.

TRK proteins - essential potassium (K(+)) transporters in fungi and bacteria, as well as in plants - are generally absent from animal cells, which makes them potential targets for selective drug action. Indeed, in the human pathogen Candida albicans, the single TRK isoform (CaTrk1p) has recently been demonstrated to be required for activity of histidine-rich salivary antimicrobial peptides (histatins). Background for a detailed molecular investigation of TRK-protein design and function is provided here in sequence analysis and quantitative functional comparison of CaTrk1p with its better-known homologues from Saccharomyces cerevisiae.

Chloride channel function in the yeast TRK-potassium transporters.

The TRK proteins-Trk1p and Trk2p- are the main agents responsible for "active" accumulation of potassium by the yeast Saccharomyces cerevisiae. In previous studies, inward currents measured through those proteins by whole-cell patch-clamping proved very unresponsive to changes of extracellular potassium concentration, although they did increase with extracellular proton concentration-qualitatively as expected for H(+) coupling to K(+) uptake. These puzzling observations have now been explored in greater detail, with the following major findings: a) the large inward TRK currents are not carried by influx of either K(+) or H(+), but rather by an efflux of chloride ions; b) with normal expression levels for Trk1p and Trk2p in potassium-replete cells, the inward TRK currents are contributed approximately half by Trk1p and half by Trk2p; but c) strain background strongly influences the absolute magnitude of these currents, which are nearly twice as large in W303-derived spheroplasts as in S288c-derived cells (same cell-size and identical recording conditions); d) incorporation of mutations that increase cell size (deletion of the Golgi calcium pump, Pmr1p) or that upregulate the TRK2 promoter, can further substantially increase the TRK currents; e) removal of intracellular chloride (e.

Killing of Candida albicans by human salivary histatin 5 is modulated, but not determined, by the potassium channel TOK1.

Salivary histatin 5 (Hst 5), a potent toxin for the human fungal pathogen Candida albicans, induces noncytolytic efflux of cellular ATP, potassium, and magnesium in the absence of cytolysis, implicating these ion movements in the toxin's fungicidal activity. Hst 5 action on Candida resembles, in many respects, the action of the K1 killer toxin on Saccharomyces cerevisiae, and in that system the yeast plasma membrane potassium channel, Tok1p, has recently been reported to be a primary target of toxin action. The question of whether the Candida homologue of Saccharomyces Tok1p might be a primary target of Hst 5 action has now been investigated by disruption of the C.

Inhibition of K/HCO(3) cotransport in squid axons by quaternary ammonium ions.

Previous squid-axon studies identified a novel K/HCO3 cotransporter that is insensitive to disulfonic stilbene derivatives. This cotransporter presumably responds to intracellular alkali loads by moving K(+) and HCO(3)(-) out of the cell, tending to lower intracellular pH (pH(i)). With an inwardly directed K/HCO(3) gradient, the cotransporter mediates a net uptake of alkali (i.

Effect of trace levels of nigericin on intracellular pH and acid-base transport in rat renal mesangial cells.

Nigericin is an ionophore commonly used at the end of experiments to calibrate intracellularly trapped pH-sensitive dyes. In the present study, we explore the possibility that residual nigericin from dye calibration in one experiment might interfere with intracellular pH (pHi) changes in the next. Using the pH-sensitive fluorescent dye 2', 7'-bis(carboxyethyl)-5,6-carboxyfluorescein (BCECF), we measured pHi in cultured rat renal mesangial cells.