A Novel Study on Intracellular Information Processing by Actin Filaments with an Extracellular Connection
Information delivery by cytoskeletal proteins have gained attention due to their potentiality for being a contributor to processing information in the intracellular environment of cells. How- ever, one area still unexplored is the connection that action potentials may have with information processed by these charged bionanowires. In this work, we study the conductive properties of actin filaments, while emerged in a aqueous electrolyte solution, for situations that may be mod- eled by invitro experiments. We develop an innovative multi-scale approach able to account for the atomistic details of a protein molecular structure, its biological environment, and their im- pact on electrical impulses in the form of ionic soliton waves. We use a perturbed Korteweg-de Vries (pKdV) differential equation to resolve a transmission line for the electric potential time evolution of the soliton along a single F-actin. Pathological conditions are studied, and an inter- active Mathematica program is provided for researchers to perform their own analysis on different nucleotide states (ATP or ADP), isoforms (alpha-smooth, alpha-skeletal, alpha-cardiac, gamma- smooth, gamma-cytoplasmic, beta-cytoplasmic), and conformation models (wild-type or mutant) of the actin monomer. While rod-like filaments are used for the majority of the studies in this work, we also provide a chapter on the semi-flexible consequences to traveling solitons. Our re- sults show cytoskeletal filaments can transport information in the form of monovalent ions by using the electrical double layer properties to contain weakly bound counterions in the diffuse layer by electrostatic forces. Additionally, the ion transport system can support the delivery of divalent ions through the condensed region of the electrical triple layer. That is, a space between the protein surface and the diffuse layer, where larger charged ions will reside due to their valency. An abrupt input voltage, which can model a sudden short voltage burst in an invitro experiment, demonstrates a travel distance of a micron, which will satisfy information transfer for local distances, like in the dendrites or at the mitochondria. Using a membrane embedded ion channel, modeled by an ex- ternal source term attached to the pKdV differential equation, we show the travel distances are longer and determined by the ion channel time duration parameter. The traveling ionic soliton that includes the external source influence shows a remarkable decoupling event producing two soliton pulses, one describing the ionic wave carrying the energy from the input voltage, while the other ionic pulse carries the energy coming from the ion channel.