Graduation Year

2019

Document Type

Dissertation

Degree

Ph.D.

Degree Name

Doctor of Philosophy (Ph.D.)

Degree Granting Department

Physics

Major Professor

Wei Chen, Ph.D.

Committee Member

Bin Xue, Ph.D.

Committee Member

Jianjun Pan, Ph.D.

Committee Member

Ghanim Ullah, Ph.D.

Keywords

Hyperpolarization of Membrane Potential, Na,K-ATPase, Oscillating Electric Field, Synchronization and Modulation, Transient Pump Current

Abstract

The Na/K pumps are essential for living system and widely expressed in all eukaryotic cell membranes. By actively transporting sodium ions out of and potassium ions into the plasma membrane, Na/K pumps creates both an electrical and a chemical gradient across the plasma membrane, which are crucial for maintaining membrane potential, cell volume, and secondary active transporting of other solutes, etc.

Previously, oscillating electric field with a frequency close to the mean physiological turnover rate was used to synchronize and modulate the Na/K pump molecules. Results showed that the turnover rate of Na/K pumps can be accelerated by folds. However, this what we called first generation synchronization modulation (SM) technique can only synchronize sodium and potassium translocations into their corresponding half cycles. The detailed location of each sodium extrusion and potassium intrusion can not be determined. As a result, the synchronized pumps were uniformly distributed, generating steady-state macroscopic currents.

Based on these studies, Dr.Chen developed a new generation synchronization modulation technique. The waveform of original SM by adding an overshoot pulse at the end of each half cycle. This overshoot pulse has a function of energy barrier which will force all of the Na/K pumps into the same state in the pumping cycle until the membrane polarity change. As a result, Na/K pump molecules are not only synchronized into half cycles of oscillating electric field, but individual steps of the pumping cycle. Accordingly, transient pump currents or so called 'pre-steady state' pump currents are generated, from which some detailed information abut the mechanism of Na/K pumps can be dissected.

In this dissertation, we firstly characterized the synchronized pump currents by modified SM. The results showed that transient currents were induced at the beginning of each half cycle as expected. The ratio between positive and negative transient currents was close to 3:2, stoichiometric number of Na/K pump. Moreover, the transient currents were significantly reduced in the presence of ouabain in a time dependent manner. In addition, by gradually increasing the frequency of SM electric field in a step-wise fashion, the synchronized pump current can be modulated to the corresponding level. Next,we utilized this technique to study some detailed mechanisms of Na/K pump, including single channel configuration in transmembrane domain and extracellular D2O effect on the turnover rate.

Lastly, we extended our study to applications of this new technique and found that the modified Synchronization Modulation technique can significantly hyperpolarize the membrane potential of skeletal muscle fiber in both physiological and high potasssium conditions. During intensive exercise, the interstitial potassium ions are accumulated and temporarily reach a high level, which will attenuate the contraction force and induce muscle fatigue. Na/K pumps are crucial in the maintenance of skeletal muscle excitability and contractility by restoring the Na and K concentration gradients. By accelerating the turnover rate of Na/K pumps, SM can efficiently re-establish the membrane potential and enhance skeletal muscle contractivity, which unleashes its potential in improving certain pathological conditions, such as exercise-induced hyperkalemia.

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