Rat Heart NCX1.1 Stoichiometry Measured in a Transfected Cell System
Expression of cDNA encoding the rat heart NCX1.1 protein in HEK-293 cells provides a simple system in which properties of the expressed protein can be determined in the absence of contaminating ionic conductances or parallel transport pathways. Using this system, we have determined that NCX1.1 transports 4 Na+ in exchange for 1 Ca2+ and accompanied by the movement of 2 positive charges. The measured stoichiometry is constant over a range of different intracellular Na+ and Ca2+ concentrations, independent of the nature of the Ca2+ buffer used and not affected by the direction of the applied voltage ramp. We conclude that our measurements are unlikely to be confounded by poor control over ionic conditions close to the intracellular surface of the membrane. A stoichiometry of 4
patch clamp reversal potential