Colloidal structure and proton conductivity of the gel within the electrosensory organs of cartilaginous fishes

Molly Phillips; Alauna C Wheeler; Matthew J Robinson; Valerie Leppert; Manping Jia; Marco Rolandi; Linda S Hirst; Chris T Amemiya

doi:10.1016/j.isci.2021.102947

Colloidal structure and proton conductivity of the gel within the electrosensory organs of cartilaginous fishes

iScience. 2021 Aug 4;24(9):102947. doi: 10.1016/j.isci.2021.102947. eCollection 2021 Sep 24.

Authors

Molly Phillips^{1

2}, Alauna C Wheeler³, Matthew J Robinson⁴, Valerie Leppert⁴, Manping Jia⁵, Marco Rolandi⁵, Linda S Hirst^{3

6}, Chris T Amemiya^{1

2

6}

Affiliations

¹ Department of Biology, University of Washington, Seattle, WA 98195, USA.
² Department of Molecular and Cell Biology, University of California, Merced, Merced, CA 95343, USA.
³ Department of Physics, University of California, Merced, Merced, CA 95343, USA.
⁴ Department of Materials Science and Engineering, University of California, Merced, Merced, CA 95343, USA.
⁵ Department of Electrical and Computer Engineering, Baskin School of Engineering, University of California, Santa Cruz, Santa Cruz, CA 95064, USA.
⁶ Quantitative and Systems Biology Program, University of California, Merced, Merced, CA 95343, USA.

Abstract

Cartilaginous fishes possess gel-filled tubular sensory organs called Ampullae of Lorenzini (AoL) that are used to detect electric fields. Although recent studies have identified various components of AoL gel, it has remained unclear how the molecules are structurally arranged and how their structure influences the function of the organs. Here we describe the structure of AoL gel by microscopy and small-angle X-ray scattering and infer that the material is colloidal in nature. To assess the relative function of the gel's protein constituents, we compared the microscopic structure, X-ray scattering, and proton conductivity properties of the gel before and after enzymatic digestion with a protease. We discovered that while proteins were largely responsible for conferring the viscous nature of the gel, their removal did not diminish proton conductivity. The findings lay the groundwork for more detailed studies into the specific interactions of molecules inside AoL gel at the nanoscale.

Keywords: Biological sciences; Colloids; Materials science; Neuroanatomy; Neuroscience; Sensory neuroscience; Zoology.