Calcium signal transmission by axonemal microtubules as an optimized information pathway in cilia and flagella.

Calcium plays a key role in signal transduction in eukaryotic cells. Besides controlling local functions of cells calcium ions are responsible for the generation of global signals such as waves and spikes. Pulsatile increases of calcium concentrations are generally considered to have a much higher fidelity of information transfer than simple tonic changes, since they are much less prone to noisy fluctuations. In that respect, it was clearly revealed that Ca2+ has very crucial involvement in many signaling pathways in cilia and flagella. We earlier established a model in which axonemal microtubules exhibit the features of nonlinear polyelectrolitic electric transmissions lines for efficient transport of cations, primarily Ca2+. These microtubules guide accumulated "ionic clods" which serve as the pulsatile signals aimed to regulate pertaining motor proteins, dyneins and kinesis. We here consider such Ca2+ signals in axoneme in the context of Shannon's and Fisher's information theories. It appears that the fast drift of these "ionic clouds" represents the optimized calcium signaling for control of "flagellary beats" as well as intraflagellary transport of proteins essential for the construction, elongation and maintenance of eukaryotic cilia and flagella themselves.