Investigating the conformational states of the rabbit Na+/glucose cotransporter.
The Na(+) and voltage-dependence of transient rabbit Na(+)/glucose cotransporter (rSGLT1) kinetics was studied with the two-electrode voltage-clamp technique and Xenopus laevis oocytes. Using step changes in membrane potential, in the absence of glucose but with 100 or 10 mM Na(+), transient currents were measured corresponding to binding/debinding of Na(+) and conformational changes of the protein. Previously, only a single time constant has been published for rSGLT1. We, however, observed three decay components; a fast (tau(f), 0.5-1 ms) voltage- and Na(+)-independent decay, and medium (tau(m), 0.5-4 ms) and slow (tau(s), 8-50 ms) voltage- and Na(+)-dependent decays. Transient currents were simulated and fit using a four-state model to obtain kinetic parameters for the system. The four-state model was able to reconstitute an assortment of experimental data.
Krofchick
Daniel
D
Institute of Biomaterials and Biomedical Engineering and Canadian Institutes for Health Research Group in Membrane Biology, Department of Medicine, University of Toronto, Toronto, Ontario, Canada.
Silverman
Mel
M
D000222:Adaptation, Physiological / Q000502:physiology; D000818:Animals; D002478:Cells, Cultured; D003198:Computer Simulation; D005947:Glucose / Q000378:metabolism*; D008562:Membrane Glycoproteins / Q000737:chemistry* / Q000145:classification / Q000502:physiology*; D008564:Membrane Potentials / Q000502:physiology*; D008954:Models, Biological; D009004:Monosaccharide Transport Proteins / Q000737:chemistry* / Q000145:classification / Q000502:physiology*; D009865:Oocytes / Q000737:chemistry / Q000502:physiology; D011487:Protein Conformation; D011817:Rabbits; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D012964:Sodium / Q000378:metabolism*; D051269:Sodium-Glucose Transporter 1; D013329:Structure-Activity Relationship; D014982:Xenopus laevis
D008562:Membrane Glycoproteins; D009004:Monosaccharide Transport Proteins; D011994:Recombinant Proteins; D051269:Sodium-Glucose Transporter 1; D012964:Sodium; D005947:Glucose