The objective of the research conducted in my laboratory is to obtain a molecular level understanding of the mechanism of ion translocation by electrogenic transport pumps.  The active transport of ions across cell membranes is important for the maintenance of electrical excitability of nerve and muscle cells and for providing the electrochemical driving force that supplies the energy required for the uptake of metabolites such as sugars and amino acids. We have identified several reaction steps in the transport cycle of the Na⁺/K⁺ pump that translocate charge and, therefore, are voltage dependent.  Surprisingly, rather than finding that charge translocation is associated with the major inside-facing to outside-facing conformational change of the enzyme, we find that the principal voltage dependent step in the pump cycle is associated with the binding of extracellular Na⁺.  The voltage dependence can be accounted for by the hypothesis that there is an external access channel (ion-well) that Na⁺ ions must enter in order to reach their binding sites.  We are investigating the ability of this hypothesis to explain steady-state and transient behavior of Na⁺/K⁺ pump current in voltage-clamped Xenopus oocytes and squid giant axons, cells that are large enough to allow both the intracellular and extracellular solutions to be controlled and the movement of substances across the membrane to be measured.

Recent Publications:

1.      Holmgren, M., J. Wagg, F. Bezanilla, R.F. Rakowski, P. De Weer and D.C. Gadsby.  Three distinct sequential steps in extracellular release of three Na⁺ ions by the Na,K-ATPase.  Nature  403:898-901 (2000).

2.      De Weer, P., D.C. Gadsby and R.F. Rakowski.  Voltage dependence of the Apparent Affinity for External Na⁺ of the Backward-running Sodium Pump.  Journal of General Physiology 117: 315-328 (2001)

3.      Vasilyev, A., E. Indyk, and R. F. Rakowski.  Properties of a sodium channel (Na_x) activated by strong depolarization of Xenopus oocytes.  Journal of Membrane Biology 185: 237-247 (2002).

4.      Rakowski, R. F., D. C. Gadsby and P. De Weer.  Single ion occupancy and steady-state gating of Na channels in squid giant axon.  Journal of General Physiology 119: 235-249, (2002).

5.      Sagar, S. and R.F. Rakowski.  Found: Na⁺ and K⁺ binding sites of the sodium pump. News in Physiological Sciences  18:164-168 (2003).