Electrical characterization of gel collected from shark electrosensors

Abstract

To investigate the physical mechanism of the electric sense, we present an initial electrical characterization of the glycoprotein gel that fills the electrosensitive organs of marine elasmobranchs (sharks, skates, and rays). We have collected samples of this gel, postmortem, from three shark species, and removed the majority of dissolved salts in one sample via dialysis. Here we present the results of dc conductivity measurements, low-frequency impedance spectroscopy, and electrophoresis. Electrophoresis shows a range of large protein-based molecules fitting the expectations of glycoproteins, but the gels of different species exhibit little similarity. The electrophoresis signature is unaffected by thermal cycling and measurement currents. The dc data were collected at various temperatures, and at various electric and magnetic fields, showing consistency with the properties of seawater. The impedance data collected from a dialyzed sample, however, show large values of static permittivity and a loss peak corresponding to an unusually long relaxation time, about 1 ms. The exact role of the gel is still unknown, but our results suggest its bulk properties are well matched to the sensing mechanism, as the minimum response time of an entire electric organ is on the order of 5 ms.

Electroreception in the Guiana dolphin (Sotalia guianensis)

“…This feature is not known in any F-SCderived structures other than the vibrissal crypts of the Guiana dolphin, but is believed to be the basis of electroreception in the platypus and the echidna [8]. In addition, an important component of ampullary canals related to the process of electroreception appears to be a glycoprotein-based gel in fish [36] and mucus in the platypus [37]. In our live Guiana dolphin, a gel-like substance was permanently emitted from the vibrissal crypts.…”

Electroreception in Elasmobranchs: Sawfish as a Case Study

“…It is a species-specific muco-polysaccharide gel [Murray, 1974] that is rich in ions and possesses electrical properties approximating those of seawater with one exception: the values of voltage noise are reduced [Brown et al, 2002]. The gel may aid in maintaining the geometry of the canals and prevents infections of otherwise vulnerable and open structures [Brown et al, 2002].…”

“…These cells are connected with each other through tight junctions and desmosomes, creating a smooth surface within the canal wall [Szabo, 1974;Waltman, 1966]. The tight junctions in the luminal region between superficial cells of the canal wall insulate the canal [Waltman, 1966]; therefore, each ampulla of Lorenzini is a well-insulated core conductor [Bodznick and Boord, 1986;Brown et al, 2002].…”

“…The connections between cells of the canal wall and the alveolar receptor epithelium provide a very high electrical resistance between the inside and the outside of the ampullary structures [Waltman, 1966;Murray, 1974], and so the ampullae are well-insulated core conductors [Bodznick and Boord, 1986;Brown et al, 2002]. The average capacity of the canal is 0.4 F cm -2 , while the resistance of the canal wall is 6 M ⍀ cm 2 , and the resistance of the gel is around 25-31 M ⍀ cm 2 [Waltman, 1966;Murray, 1974].…”

Electroreception in the euryhaline stingray, Dasyatis sabina

“…A single ampulla consists of multiple alveolar sacs continuous with a narrow canal that terminates in a pore on the skin surface (Waltman, 1966). The canal wall is comprised of cells that are bound by tight junctions that form a higher impedance electrical barrier than the glycoprotein gel within the canal (Murray and Potts, 1961;Waltman, 1966;Brown et al, 2002). The lumen of the ampulla is lined by a single-layer epithelium that is comprised of sensory and support cells (Waltman, 1966;Zakon, 1988;New and Tricas, 2001).…”