Calcium ions tune the beats of cilia and flagella

Abstract

The cytoskeleton of cilia and flagella is so called axoneme a stable cylindrical architecture of nine microtubule doublets. Axoneme performs periodic bending motion by utilizing specific dynein motor family powered by ATP hydrolysis. It is still unclear how this highly organized "ciliary beat" is being initiated and strongly coordinated by the combined action of hundreds dynein motors. Based on the experimental evidences we here elaborate a plausible scenario in which actually calcium ions play the roles of catalytic activators and coordinators of dynein attachments doing it in superposition with already known mechanical control tools of "ciliary beat". Polyelectrolyte properties of microtubules incorporated in axoneme doublets enable the formation and propagation of soliton-like "ionic clouds" of Ca²⁺ ions along these "coaxial nanocables". The sliding speed of such Ca²⁺ "clouds" along microtubule doublets is comparable with the speed of propagation of "ciliary beat" itself. We elaborated the interplay between influx of Ca²⁺ ions in ciliary based body and the sliding of microtubule triplets therein. In second segment we considered how the dynein motors activated by Ca²⁺ ions contained within solitonic "ionic clouds" in competition with axoneme curvature regulate ciliary and flagellar beating.

Keywords: Axoneme; Ionic cloud; Microtubule; Nonlinear electric transmission line.