Flexibility and Constraint in the Interpretation of Na+/K+ Pump Electrogenicity: What is an Access Channel?
A central question which electrophysiologists ask about the Na+/K+ pump often appears esoteric: How and when do ions cross the membrane electrical field during the pump cycle? From the electrophysiologist’s view point, this question challenges profoundly our understanding of the molecular basis of ion transport. The reasons are apparent when pump function is thought of as a selective, stoichiometric movement of ions across the cell membrane barrier, and therefore across membrane electrical field. Several electrophysiological approaches have raised questions and suggested hypotheses about molecular structure-function relations of the Na+/K+ pump. Recently, it has been proposed that the major chargecarrying reaction of the Na+/K+ pump is the diffusion of sodium through a ’high resistance access channel’, open to the extracellular side in the E2 pump state (1). The present article will describe some of the flexibilities and constraints encountered by the author in accounting for recent experimental results on Na+/K+ pump electrogenicity with the help of simulations. The results considered will include refined charge movement measurements in giant cardiac membrane patches.
KeywordsDehydration Stein Seco Ouabain Hines
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