Why Olfactory Cilia Use Outward-Flowing Cl−, Not Inward-Flowing Na+, to Generate Current; Need for Consistent Response in Variable Environments & Tiny Volume of Cilia Are Key; Findings Relevant to Nerve-Ending Pathology in Neurodegenerative Disease

Imagine trying to figure out how something works when that something takes place in a space smaller than a femtoliter: one quadrillionith of a liter. Now, two scientists with a nose for solving mysteries have used a combination of mathematical modeling, electrophysiology, and computer simulations to explain how cells communicate effectively in highly constricted spaces such as the olfactory cilia, where odor detection takes place. The findings will inform future studies of cellular signaling and communication in the olfactory system and also in other confined spaces of the nervous system. Study co-author Johannes Reisert, PhD, a Monell Chemical Senses Center cell physiologist, comments, "Ion channels and how their currents change ion concentrations inside cells are notoriously difficult to study. Our modeling-based approach enables us to better understand, not only how olfaction works, but also the function of small nerve endings such as dendrites, where pathology is associated with many neurodegenerative diseases." In the study, published online on December 31, 2018 in PNAS, the scientists asked why olfactory receptor cells communicate with the brain using a fundamentally different series of electrical events than used by sensory cells in the visual or auditory systems. The article is titled “Ca2+-Activated Cl− Current Ensures Robust and Reliable Signal Amplification in Vertebrate Olfactory Receptor Neurons.” Olfaction begins when, in a process similar to a key fitting into a lock, an airborne chemical molecule travels through the nasal mucus to bind with an olfactory receptor embedded on the wall of a nerve cell within the nose. The olfactory receptors are located on cilia, elongated super-thin threadlike structures less than 0.000004 inches in diameter, which extend from the nerve cell into the mucus.
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