Abstract
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 ( τ f, 0.5–1 ms) voltage- and Na +-independent decay, and medium ( τ m, 0.5–4 ms) and slow ( τ 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.
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