Mackenzie, Loo, Panayotova-Heiermann, Wright,

Model Status

This CellML model has been curated, the units are consistent and the model runs in COR and PCEnv. This model recreates the published results.

Model Structure

Abstract: The Na-dependent, low affinity glucose transporter SGLT2 cloned from pig kidney is 76% identical (at the amino acid level) to its high affinity homologue SGLT1. Using two-microelectrode voltage clamp, we have characterized the presteady-state and steady-state kinetics of SGLT2 expressed in Xenopus oocytes. The kinetic properties of the steady-state sugar-evoked currents as a function of external Na and a-methyl-D-glucopyranoside (aMG) concentrations were consistent with an ordered, simultaneous transport model in which Na binds first. Na binding was voltage-dependent and saturated with hyperpolarizing voltages. Phlorizin was a potent inhibitor of the sugar-evoked currents (Ki ~10 mM) and blocked an inward Na current in the absence of sugar. SGLT2 exhibited Na-dependent presteadystate currents with time constants 3-7 ms. Charge movements were described by Boltzmann relations with apparent valence ~1 and maximal charge transfer ~11 nC, and were reduced by the addition of sugar or phlorizin. The differences between SGLT1 and SGLT2 were that (i) the apparent affinity constant (K0.5) for aMG (~3 mM) was an order of magnitude higher for SGLT2; (ii) SGLT2 excluded galactose, suggesting discrete sugar binding; (iii) K0.5 for Na was lower in SGLT2; and (iv) the Hill coefficient for Na was 1 for SGLT2 but 2 for SGLT1. Simulations of the six-state kinetic model previously proposed for SGLT1 indicated that many of the kinetic properties observed in SGLT2 are expected by simply reducing the Na/glucose coupling from 2 to 1.

The original paper reference is cited below:

Biophysical Characteristics of the Pig Kidney Na/Glucose Cotransporter SGLT2 Reveal a Common Mechanism for SGLT1 and SGLT2, M. Mackenzie, D.D.F. Loo, M. Panayotova-Heiermann, and E. M. Wright, 1996, Journal of Biological Chemistry, 271, 32678-32683. PubMed ID: 8955098

Schematic diagram of the Mackenzie et al 1996 SGLT2 model. C' represents the external-facing carrier. C'' represents the internal-facing carrier.