Document Type

Article

Publication Title

Journal of Biological Chemistry

Publication Date

1996

Volume

271

Issue

25

Disciplines

Medical Sciences | Medicine and Health Sciences | Pharmacy and Pharmaceutical Sciences

Abstract

Voltage clamp recording was used to measure steady-state and presteady-state currents mediated by a myo-inositol transporter cloned from Leishmania donovani and expressed in Xenopus oocytes. Application of myo-inositol resulted in inward currents, which did not require external sodium and which were increased by increasing the extracellular proton concentration and by membrane hyperpolarization. Alkalinization of the extracellular space occurred concomitantly with myo-inositol influx. Correlation of membrane currents with radiolabeled myo-inositol flux revealed that one positive charge is translocated with each molecule of myo-inositol, consistent with cotransport of one proton. The transport concentration dependence on both species suggested ordered binding of a proton followed by a molecule of myo-inositol. In the absence of myo-inositol, a voltage-dependent capacitance was observed that correlated with the transporter expression level. This charge movement obeyed a Boltzmann function, which was used to estimate a turnover of 0.70 ± 0.06 s−1 at −60 mV. The pH and voltage dependence of the charge movements were simulated with a model involving alternating access of internal and external protons to sites within an occluded pore.

DOI

10.1074/jbc.271.25.14937

Rights

© 1996 by The American Society for Biochemistry and Molecular Biology, Inc.

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