Ionic Waves Propagation Along the Dendritic Cytoskeleton as a Signaling Mechanism

We outline the physical conditions that enable cytoskeletal polymers, such as actin filaments (AFs) and microtubules, to act as electrical transmission lines for ion flows along their lengths. For AFs we propose a model in which each protein subunit is an electric element with a capacitive, inductive, and resistive property due to the molecular structure of the filament and viscosity of the solution. Based on the conductivity rules that apply to electrical circuits, we discuss the properties of ionic waves that propagate along actin filaments. We then discuss the dynamics of C-termini states in microtubules and their networks, including the interactions with ions and signal transmission via microtubule-associated proteins. Experiments on ionic conductivity along AFs and microtubules validate the basic assumptions postulated in our models. As a consequence of these results we propose a new signaling mechanism in the cell, especially in neurons, that involves clouds of ions surrounding protein filaments which may travel without significant decay along the axon or the dendritic tree. These signals may be utilized to control various membrane properties, for example, the transition rate of ion channel opening and closing, local membrane conductivity, and vesicle trafficking.