Potassium Channel And Its Study Of Permeation

Ion channels are membrane-spanning proteins that can selectively mediate ion flux between the outside and inside of the phospholipid bilayer, and are essential for the electric activities of the organism. In this paper, the basic knowledge and several main theoretical approaches about ion channel are firstly introduced. Then, based on the latest high-resolution, three-dimension crystal structure of KcsA potassium channel, a three-state hopping model is established to study permeation of an open-state potassium channel. Breaking through other theories, we innovatively choose the master equation to characterize the dynamics of the system and educe the results according with experiments and the study of the others. In this model, ion conduction involves transitions of three states, with one three-ion state and two two-ion states in the selectivity filter respectively. In equilibrium, the well-known Nernst equation is deduced. In the study, it is further shown that the current follows Michaelis-Menten kinetics in steady state. Using the KcsA K+permeation parameters provided by P.H.Nelson [1], the current-voltage relationship is proved to be ohmic and the concentration-current relationship are also obtained reasonably. In addition, the steady state characters have been the central problem in the past years, while the transient, short-time behaviors are seldom considered. In this paper, using the three-state hopping model firstly, we discuss the characteristic time to reach the steady state for the potassium channel and illuminate the validation of the model to transient behaviors. The aim of this paper is to offer a valid method for the permeation study of ion channel and to suggest a possible physical base for the function-structure relationship of ion channel. The study of this problem will make clear the transport mechanism of substance and information in cell membrane and help human being understand the essence of life activities.