Sharks, skates, and rays can detect very weak electric fields produced by prey and other animals using an array of unusual organs known as the ampullae of Lorenzini.
Exactly how these electrosensory organs work has remained a mystery, but a new study reveals an important clue.
The ampullae of Lorenzini are visible as small pores in the skin around the head and on the underside of sharks, skates, and rays (known as elasmobranchs, a subclass of cartilaginous fish). Each pore is connected to a set of electrosensory cells by a long canal filled with a clear, viscous jelly.
In the new study, published in Science Advances, a team of researchers reports that the jelly is a remarkable proton-conducting material, with the highest proton conductivity ever reported for a biological material. Its conductivity is only 40 times lower than the current state-of-the-art proton-conducting polymer Nafion, says corresponding author Marco Rolandi, an affiliate associate professor of materials science and engineering at the University of Washington and an associate professor of electrical engineering at UC Santa Cruz.
“The observation of high proton conductivity in the jelly is very exciting,” Rolandi says. “We hope that our findings may contribute to future studies of the electrosensing function of the ampullae of Lorenzini and of the organ overall, which is itself rather exceptional.”
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The integration of signals from several ampullae allows sharks, skates, and rays to detect changes in the electric field as small as 5 nanovolts per centimeter. But how such weak signals are transmitted from the pore to the sensory cells has long been a matter of debate. The researchers speculate that sulfated polyglycans in the jelly may contribute to its high proton conductivity.
Proton conductivity is the ability of a material or solution to conduct protons (positive hydrogen ions). In a system with very many ordered hydrogen bonds, such as a hydrated hydrophilic polymer, proton conduction can occur along chains of these bonds, Rolandi explains. In technological applications, proton conductors such as Nafion can be used as proton exchange membranes in fuel cells.
“The first time I measured the proton conductivity of the jelly, I was really surprised,” says first author Erik Josberger, an electrical engineering doctoral student in Rolandi’s group. “I didn’t expect a natural material to approach the proton conductivity of an engineered material like Nafion.”
The new findings may be of interest to researchers in materials science and other fields. Applications of the discovery could include unconventional sensor technology, Rolandi says.
Coauthors of the paper are from the University of Washington, UC Santa Cruz, and the Benaroya Research Institute at Virginia Mason in Seattle. The National Science Foundation, the Office of Naval Research, and the National Institutes of Health supported the work.
Source: University of Washington