Relationships Between Na+/Glucose Cotransporter (SGLT1) Currents and Fluxes (original) (raw)

Abstract.

The relationships between currents generated by the rabbit Na+/glucose cotransporter (SGLT1) and the fluxes of Na+ and sugar were investigated using Xenopus laevis oocytes expressing SGLT1. In individual voltage-clamped oocytes we measured: (i) the current evoked by 10 mmαMG and the 22Na+ uptake at 10 mm Na+; (ii) the currents evoked by 50 to 500 μm [14C]αMG and the [14C]αMG uptakes at 100 mm Na+; and (iii) phlorizin-sensitive leak currents in the absence of sugar and 22Na+ uptakes at 10 mm Na+. We demonstrate that the SGLT1 leak currents are Na+ currents, and that the sugar-evoked currents are directly proportional to both αMG and Na+ uptakes. The Na+/αMG coupling coefficients were estimated to be 1.6 at −70 mV and 1.9 at −110 mV. This suggests that the rabbit SGLT1 Na+/αMG stoichiometry for sugar uptake is 2 under fully saturating, zero-trans conditions. Coupling coefficients of less than 2 are expected under nonsaturating conditions due to uncoupled Na+ fluxes (slippage). The similarity between the Na+ Hill coefficients and the coupling coefficients suggests strong cooperativity between the two Na+ binding sites.

Access this article

Log in via an institution

Subscribe and save

Buy Now

Price excludes VAT (USA)
Tax calculation will be finalised during checkout.

Instant access to the full article PDF.

Similar content being viewed by others

Author information

Authors and Affiliations

  1. Department of Physiology, UCLA School of Medicine, Center for the Health Sciences, Los Angeles, California 90095-1751, USA, , , , , , US
    B. Mackenzie, D.D.F. Loo & E.M. Wright

Authors

  1. B. Mackenzie
  2. D.D.F. Loo
  3. E.M. Wright

Additional information

Received: 6 October 1997/Revised: 5 December 1997

Rights and permissions

About this article

Cite this article

Mackenzie, B., Loo, D. & Wright, E. Relationships Between Na+/Glucose Cotransporter (SGLT1) Currents and Fluxes.J. Membrane Biol. 162, 101–106 (1998). https://doi.org/10.1007/s002329900347

Download citation