Quantitative Modeling of Chloride Conductance in Yeast TRK Potassium Transporters

¹ Yale School of Medicine
² Yale Univ. Sch. of Med.
³ Gene Research Center, Okayama University, Japan

^* To whom correspondence should be addressed. E-mail: clifford.slayman{at}yale.edu.

Submitted on May 17, 2005
Revised on June 13, 2005
Accepted on 6 July 2005

	Abstract

So-called TRK proteins are responsible for "active" accumulation of potassium in plants, fungi, and bacteria. A pair of these proteins in the plasma membrane of Saccharomyces, ScTrk1p and ScTrk2p, also admit large, adventitious, chloride currents during patch recording (Cl^- efflux; J. Membr. Biol. 198:177, 2004). Resulting steady-state current-voltage curves can be described by two simple kinetic models, most interestingly, voltage-driven "channeling" of ions through a pair of activation-energy barriers that lie within the membrane dielectric, near the inner () and outer () surfaces. Two barrier heights (E and E) and two relative distances (a₁ and b₂) from the surfaces specify the model. Measured current amplitude parallels intracellular chloride concentration and is strongly enhanced by acidic extracellular pH. The former implies an exponential variation of a₁, between ~0.2 and ~0.4 of the membrane thickness, while the latter implies a linear variation of E, by 0.69 Kcal.mol^-1/pH. The model requires membrane slope conductance to rise exponentially with increasingly large negative membrane voltage, as verified by data from a few yeast spheroplasts which tolerated voltage clamping at -200 to -300 mV. The behaviors of E and a₁ accord qualitatively with a hypothetical structural model for fungal TRK proteins (Biophys. J. 77:789-807, 1999), suggesting that chloride ions flow through a central pore formed by symmetric aggregation of four TRK monomers.

Key Words: Chloride channel, Energy barriers, Patch-clamping, Saccharomyces, TRK proteins, pH-gating

This article has been cited by other articles:

				M. L. Jennings and J. Cui Chloride Homeostasis in Saccharomyces cerevisiae: High Affinity Influx, V-ATPase-dependent Sequestration, and Identification of a Candidate Cl- Sensor J. Gen. Physiol., March 31, 2008; 131(4): 379 - 391. [Abstract] [Full Text] [PDF]