Symmetry of H+ Binding to the Intra- and Extracellular Side of the H+-coupled Oligopeptide Cotransporter PepT1

• DOI: 10.1074/jbc.272.12.7777
• Publication Date: 2002-07-26T14:49:13Z
• Authors: Stephan Nussberger; Angela Steel; Davide Trotti; Michael F. Romero; Walter F. Boron; Matthias A. Hediger
• Keywords: Reversal potential; Surface charge

Ion-coupled solute transporters exhibit pre-steady-tate currents that resemble those of voltage-dependent ion channels. These were assumed to be mostly due binding and dissociation the coupling near extracellular transporter surface. Little attention was given analogous events may occur at intracellular To address this issue, we performed voltage clamp studies Xenopus oocytes expressing intestinal H+-coupled peptide cotransporter PepT1 recorded dependence transient charge movements in absence substrate on changing intra- (pHi) pH (pHo). Rapid steps membrane potential induced showed a marked pHi pHo. At pHo 7.0 holding (Vh) −50 mV, inwardly directed, whereas reduction below resulted outwardly directed movements. When reduced, observed. The data fitted by Boltzmann equation, yielding an apparent valence 0.65 ± 0.03 (n = 7). midpoint (V0.5) distribution shifted linearly as function Our results indicate that, first approximation, magnitude polarity depend upon prevailing H+ electrochemical gradient. We propose has single proton site is symmetrically accessible from both sides decreasing chemical (ΔμH) or increasing (Vm) shifts facing occluded state. This concept constitutes important extension previous kinetic models ion-coupled including more detailed description events.