Structural Characteristics and Proton Conductivity of the Gel Within the Electrosensory Organs of Cartilaginous Fishes

Abstract

The Ampullae of Lorenzini (AoL) of cartilaginous fishes are sensory organs used to detect environmental electric fields. The proximal ends of the organs are externally visible as pores in the skin that lead into gel-filled tubular canals which terminate in rounded chambers filled with highly specialized electrosensory cells. The viscoelastic gel that fills the organs is composed of proteins and polysaccharides that are not yet completely characterized but are thought to play a critical role in the electrosensing mechanism. Although recent studies have identified various components of AoL gel, it has remained unclear how the component molecules are structurally arranged and how their structure influences the overall function of the AoL. Here we present the first microscopic descriptions and x-ray scattering data from AoL gel extracted from spotted ratfish (Hydrolagus colliei). Our results suggest that AoL gel is colloidal in nature and composed of spherical globules that are approximately 10-100 nm in size. We investigated the structural influence of the protein components of the gel specifically by analyzing gel that had been digested in situ via enzymatic proteolysis. By comparing gel before and after digestion using microscopy, x-ray scattering analyses, and proton conductivity measurements, we directly observed the structural and functional influence of proteins in AoL gel. The findings described here represent the first detailed structural analysis of AoL gel and lay the groundwork for more detailed studies into the specific interactions of molecules inside AoL gel at the nanoscale, with particular reference to their mechanistic role in electrosensing.

Diverse Proton-Conducting Nanotubes via a Tandem Macrocyclization and Assembly Strategy

“…These observations are fingerprints of proton conductivity, a phenomenon which was further validated by observing a sharp decrease in conductivity due to isotope effects when the same measurements were carried out in the presence of D 2 O (Figure S134). − The measured deuterium effect is as expected for protons being the major charge carrier within the nanotubes and rules out the possibility that other ions, such as ions present in the solvent or the acid counterion, contribute substantially to the measured current. All samples demonstrate the hallmarks of proton conductivity, and our observations suggest that the conductivity values of various nanotubes have a pore size dependence.…”

Natural biopolymers as proton conductors in bioelectronics

“…[124] Furthermore, Amemiya and co-workers did the first structural study on AoL gel to decode the influence of various polysaccharides and proteins on their proton conduction. [125] By measuring the proton conductivity properties of the gel before and after digestion with proteolytic enzymes, they discovered the removal of proteins did not diminish proton conductivity.…”