First structural study of gel inside the electro sensory organs of cartilaginous fishes*

Cartilaginous fishes detect electric fields in their environment using the sensory organs called Ampullae of Lorenzini (AoL). Although the organs were discovered hundreds of years ago, little is known about the gel inside the AoL. Some components of the gel have been identified recently, including chitin and other polysaccharides, but the structure of the gel is yet unknown. Using data collected from atomic force microscopy (AFM), proton conductivity, and x-ray scattering experiments, we present the first microscopic descriptions of the AoL gel structure. We include an investigation of the structural influence of the protein components in the gel by comparing the data of the gel with data from aliquots digested with proteolytic enzymes. We find evidence that the AoL gel is colloidal in nature, stabilized by a protein network.