Abstract
Cilia are hairlike organelles involved in both sensory functions and motility. We discuss the question of whether the location of chemical receptors on cilia provides an advantage in terms of sensitivity and whether motile sensory cilia have a further advantage. Using a simple advection-diffusion model, we compute the capture rates of diffusive molecules on a cilium. Because of its geometry, a non-motile cilium in a quiescent fluid has a capture rate equivalent to a circular absorbing region with ∼4× its surface area. When the cilium is exposed to an external shear flow, the equivalent surface area increases to ∼6×. Alternatively, if the cilium beats in a non-reciprocal way in an otherwise quiescent fluid, its capture rate increases with the beating frequency to the power of 1/3. Altogether, our results show that the protruding geometry of a cilium could be one of the reasons why so many receptors are located on cilia. They also point to the advantage of combining motility with chemical reception.
Highlights
Cilia are small hairlike organelles with a microtubule-based core structure that protrude from the cell surface
By using analytical arguments and numerical simulations, we show that the capture rate of a cilium is significantly higher than that of a receptor located on a flat epithelial surface
We discuss scenarios where the fluid and the cilium are at rest, where the fluid exhibits a shear flow, where the cilium is actively beating, and where a bundle of hydrodynamically interacting cilia absorbs particles
Summary
Cilia are small hairlike organelles with a microtubule-based core structure that protrude from the cell surface. Of which there is only one on each cell, have primarily sensory functions (as receptors for chemical, mechanical, or other signals) (Zimmermann, 1898; Berbari et al, 2009; Hilgendorf et al, 2016; Spasic and Jacobs, 2017; Ferreira et al, 2019). Due to their shape and their role in signalling, they are often referred to as “the cell’s antenna” (Marshall and Nonaka, 2006; Malicki and Johnson, 2017). Some chemosensory systems, including vomeronasal (Leinders-Zufall et al, 2000) and olfactory neurons (Bhandawat et al, 2010) and marine sperm cells (Kaupp et al, 2003), are known to achieve a sensitivity high enough to detect a small number of molecules
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