Possible role of surface electrochemical electron-transfer and semiconductor charge transport processes in ion channel function

Abstract

Conductivity measurements and theoretical electronic structure calculations have been made in proteins, the calculations giving allowed energies for electrons that would enable them to participate in charge transport processes, probably by hopping and with close similarity to amorphous semiconductors. These theoretical computations have confirmed that the experimental results are probably due to electronic conduction. The foregoing considerations allow us to describe the protein-electrolyte interface as a semiconductor-electrolyte interface. Electron-transfer (ET) at such interfaces has been studied and experimentally established to occur from semiconductor electronic energy states to redox energy states in solution, or to redox surface states. ET has also been measured between organic and biochemical conducting compounds (particularly proteins and conducting membranes) and electrodes or redox solutions. Therefore, it is assumed in this paper that ET occurs at the ion channel protein interfaces with the cytoplasm and extracellular electrolytes, and that electron transport processes occur through the channel α-helices. A possible ET mechanism is proposed involving surface state oxygen-derived free radicals like Superoxide. The mathematical expressions for the biophysical phenomena discussed give two time-varying interface potentials and charge distributions that could provide the energy for the conformational changes that open and close the channel; these potentials could also change the ion permeation energy barriers by electrostatic influence. An expression is thus obtained for channel conductance as a function of membrane and interface potentials. Using this expression for sodium and potassium complemented by the usual passive components, gives a mathematical model that produces action potentials, intrinsic repetitive firing, and bursting, all of which can be modulated by changes in the biophysical parameters. Implications for ionic channel voltage gating are discussed and compared with existing experimental results and models. The possible relationships with redox and oxygen sensitivities, superoxide oxidative stress and neurotoxicity, drug and neurotransmitter effects, and ionic channel modulation are also discussed.