Table of Contents
Journal of Biophysics
Volume 2013, Article ID 683256, 14 pages
http://dx.doi.org/10.1155/2013/683256
Research Article

Transport Reversal during Heteroexchange: A Kinetic Study

1Department of Physics, UPR, San Juan, PR 00931, USA
2Department of Biochemistry, UCC, Bayamon, PR 00960, USA
3Department of Physiology, UCC, Bayamon, PR 00960, USA

Received 21 May 2013; Revised 18 August 2013; Accepted 18 August 2013

Academic Editor: Kuo-Chen Chou

Copyright © 2013 V. Makarov et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

It is known that secondary transporters, which utilize transmembrane ionic gradients to drive their substrates up a concentration gradient, can reverse the uptake and instead release their substrates. Unfortunately, the Michaelis-Menten kinetic scheme, which is popular in transporter studies, does not include transporter reversal, and it completely neglects the possibility of equilibrium between the substrate concentrations on both sides of the membrane. We have developed a complex two-substrate kinetic model that includes transport reversal. This model allows us to construct analytical formulas allowing the calculation of a “heteroexchange” and “transacceleration” using standard Michaelis coefficients for respective substrates. This approach can help to understand how glial and other cells accumulate substrates without synthesis and are able to release such substrates and gliotransmitters.