The little pores known as ampullae of Lorenzini (AoL) that dot the heads and noses of sharks, rays, and skates (collectively known as elasmobranchs) have long been known to be able to detect electrical currents in some fashion and aid in prey detection. But the mystery of exactly how they do so may now be solved. Scientists studying these bizarre organs have discovered that a particular jelly tucked inside the pores is highly conductive to protons—an uncommon occurrence in nature—and it is so far the most highly proton-conductive biological material ever reported. Their findings are published today in Science Advances. Named after the 17th century Italian ichthyologist who described them, each ampulla organ is composed of an open pore that is attached to a little sac of electrosensitive cells. Connecting the pore to the cell bundle is a fleshy canal filled with the mysterious jelly that was the focus of this study. The jelly itself is viscous, clear, and largely full of water. Although the purpose of the AoL has been known for some time, how the jelly fits into that hasn’t. So researchers from UC Santa Cruz, the University of Washington (UW), and the Benaroya Research Institute at Virginia Mason went to work to see if they could crack the case of this peculiar gel. After squeezing out gobs of jelly from pores on the noses and heads of a bonnethead shark (Sphyrna tiburo), a longnose skate (Raja rhina), and a big skate (Raja binoculata), they subjected the puzzling goo to a series of electrical tests. The scientists found the jelly to be highly proton-conductive. In fact, it appears to have the highest proton conductivity ever found in a biological material, and it’s only slightly less conductive than the state-of-the-art synthetic conducting polymer we use in fuel cells. “The first time I measured the proton conductivity of the jelly, I was really surprised,” said electrical engineering doctoral student and first author Erik Josberger of UW in a statement. Marco Rolandi, an associate professor of electrical engineering at UC Santa Cruz and corresponding author of the study, thinks that perhaps keratan sulfate, a carbohydrate found in high concentrations in the jelly, might contribute protons of its own to the water mixed in with the gel, thus making it more conductive. “It has an acid group that might donate protons,” he surmised. In a separate statement, Rolandi summed up the findings by saying that “the observation of high proton conductivity in the jelly is very exciting,” and explained further that it could be useful in materials science, or for unconventional sensor technology. As sharks prowl corals, shallow seas and the open ocean, the electrical disturbances in their watery surroundings are picked up by the jelly in the ampullae of Lorenzini and transferred to the electrosensitive cells at their base. All the pores covering their nose and heads form a network of jelly-filled canals that integrate multiple electrical signals at a time, allowing these master predators to detect changes in the electrical field of as small as 5 nanovolts per centimeter. “Ampullae of Lorenzini are quite exceptional electric field sensors,” says Rolandi. It’s just one more weapon in the evolutionary arsenal that has allowed these ancient predators to persist for hundreds of millennia.
