Meeting Abstract

53-2   13:45 - 14:00  How the lateral line doesn't work Lunsford, ET*; Bobkov, YV; Strother, JA; Liao, JC; University of Florida, Whitney Laboratory for Marine Bioscience, St. Augustine, FL; University of Florida, Whitney Laboratory for Marine Bioscience, St. Augustine, FL; University of Florida, Whitney Laboratory for Marine Bioscience, St. Augustine, FL; University of Florida, Whitney Laboratory for Marine Bioscience, St. Augustine, FL elunsford@ufl.edu http://lunsfordlab.squarespace.com

Mechanoreceptors like the hair cells of the lateral line system functions by exchanging ions across their membrane to convert physical stimuli into electrical signals. Hair cells of superficial neuromasts in zebrafish are exposed to a freshwater environment, unlike the homologous cochlear hair cells which are bathed in a high concentration of potassium (K⁺ ~ 150 mM). Despite the difference in external media, their transduction mechanisms are assumed to both be driven by an inward K⁺ current. Freshwater K⁺ concentrations (0.02 mM) are not high enough (10-20 mM) to drive K⁺ influx into lateral line hair cells, but afferents still respond to cupula deflection. It has been suggested lateral line hair cell activation is facilitated by a K⁺ rich microenvironment maintained in the cupula. However, by quantifying the movement of a small fluorophore through the cupula we reveal it is exceedingly diffusive thus rendering active maintenance unlikely. We systematically characterized the internal and external ionic environment using ion selective probes (K⁺, Na⁺, Ca²⁺, H⁺, Cl^-) and found no evidence of an ion gradient within the cupula. Functional calcium imaging and electrophysiology illustrated hair cell stimulation persists in ion deficient saline suggesting there is an alternative mechanism at play. Other sensory systems that are also exposed to the external environment, like the olfactory system, rely on anion efflux for activation which has been shown to be a more robust mechanism of transduction. Analysis of the hair cell transcriptome uncovered an overabundance of chloride (Cl^-) channel expression. Mounting evidence from pharmacological experiments suggests lateral line hair cells maintain elevated concentrations of intracellular Cl^- that efflux during lateral line deflection. We propose this is a novel mechanism of mechanotransduction.