A living model of electrophysiology

The electric eel, Electrophorus electricus, is the main bioelectricity generator in the animal kingdom, with a capacity to generate an electrical potential of up to 600 volts. Its anatomy and physiology rely on organs that develop from the skeletal muscle and preserve much of the biochemical and morphological properties of the muscular sarcolemma which is defined as a plasma membrane of the muscle fiber, coating them. This membrane plays an important role in the conduction of the electrical impulse, which leads to muscle contraction. In addition, these animals have electrolytes (electroplates), specialized cells responsible for generating electrical discharges. The teleostee electroplates evolved with excessive amounts of specific membrane proteins, promoters of a polarization that allows these cells to produce transcellular potentials which, when added in series, result in a powerful electrical discharge throughout the entire body of the animal. The electric eel uses this voluntary production of electricity as an effective mechanism to defend itself from predators and hunt its prey (Gotter et al., 1998).

Throughout history, the species of Electrophorus electricus contributed to the understanding of electricity. In 1775, John Walsh used the electric eel as a source of electrical potential, comparable to a high-powered battery. In this context, several experiments were carried out, of which one investigation stood out by involving ten people establishing physical contact in a circle, where the first and last touched respectively the head and tail of the eel - all received a light electric shock. Thus, after numerous studies, it was determined that the electrical tissue offers a suitable model for the study of biochemistry and electrophysiology of excitable membranes, due to the amount of membrane proteins homologous to other excitable tissues, in addition to cells containing large amounts of ATPases proteins. It was then concluded that the electrical tissue of Electrophorus electricus is specialized exclusively for membrane excitability (Voss et al., 1974; Gotter et al., 1998). 

Due to its specialization in generating a potential of up to 600 volts, the electrical organs prevail in about 80% of the animal’s back while the viscera are concentrated in the previous 20%. Your muscular digestive tract protrudes caudally and bends again towards the oral cavity, ending in the anus that is located just behind the head, before the small pectoral fins. The electric eel also has a swim bladder that extends along the length of the animal, between the main electrical organ and the spinal cord (Gotter et al., 1998). 

The central nervous system of the electric eel includes a small encephalon consistent with the class of teleosteos, in addition to the spinal cord that extends along the entire tail. These animals have a central control nucleus, located in the oblong medulla bulb, and is responsible for coordinating the electrical discharge. Central efferent neurons extend caudally through the spinal cord and perform synapses with motor neurons, which occupy the dorsomedial region along the length of the spinal cord. Thus, axons of some of these electromotive neurons radiate to the electrical organs and innervate electrolytes (Oliveira, 1961).

These individuals have three well-defined electrical organs, which are: 

a main electrical organ, which generates high voltage discharges, while the Hunter and Sachs organs generate low voltage discharges and are believed to be involved in electrolocation (Bennett, 1971). The main one extends from the peritoneal region along the animal’s tail, where it gives rise to the Sachs organ, which occupies the remaining portion of the caudal part, and presents a more translucent morphology due to its lower amount of densely packed electrolytes. Hunter’s organ is located adjacent to the other electrical organs, and among the three, it is the smallest viscera. Hunter’s organ is visually separated from the main organ by two sets of electrolyte beams, running along the lower edge of the main organ. To generate a synchronized electric discharge, the individual electroplates inside each electrical organ must be excited simultaneously. This synchronized stimulation is obtained by delaying the activation of proximal regions of electrical organs, allowing the electrolytes to be stimulated at the same time as those in more distant regions (Keynes, 1961; Gotter et al., 1998).

Thus, it is concluded that the specimens of Electrophorus electricus represent a living biological model for studies in bioelectricity and electrophysiology. These teleostous fish have an adapted anatomy that, associated with the functionality of the electrical organs, as well as the neuromuscular coordination of discharges, highlights the complexity of the defense mechanisms, predation and even foraging of these animals. In addition, its historical and scientific contribution reinforces the importance of this species in research on excitable membranes and electrogenic systems, capable of generating electrical potentials through physiological processes.

FIG. 1. Anatomy of the electric eel. (A) Diagram illustrating the anatomical organization of electrical organs. (B) A section through the middle portion of the eel, drawn so that the front surface is facing right. (C) Columns of electrolytes extend along the main electrical organ. In this panel, the posterior surface of an electrolyte is shown exposed and innervated by numerous electromotor axons (not shown). Thick black lines indicate isolation septa separating adjacent columns of electrolytes. The light blue shadow represents the interior of the electrolytes exposed in the cross-sectional section. Source: Gotter et al., 1998.

Author: Giovanna Luiza - Director of GEAS Brasil Association.

April/2025 Wild Panel.

Bibliographical references:

GOTTER, A. L.; KAETZEL, M. A.; DEDMAN, J. R. Electrophorus electricus as a model system for the study of membrane excitability. Brazilian Journal of Medical and Biological Research, Ribeirão Preto, v. 31, n. 3, p. 325–338, Mar. 1998. https://doi.org/10.1590/S0100-879X1998000300001.

BENNETT, M. V. L. Electric organs. In: HOAR, W. S.; RANDALL, D. J. (ed.). Fish Physiology. New York: Academic Press, 1971. v. 5, p. 347–491.

VOSS, H. G.; ASHANI, Y.; WILSON, I. B. A covalent affinity technique for the purification of all forms of acetylcholinesterase. Methods in Enzymology, v. 34, p. 581–591, 1974.

KEYNES, R. D. The development of the electric organ in Electrophorus electricus. In: CHAGAS, C.; PAES DE CARVALHO, A. (eds.). Bioelectrogenesis. New York: Elsevier Science, 1961. p. 14–19.

OLIVEIRA CASTRO, G. Morphological data on the brain of Electrophorus electricus. In: CHAGAS, C.; PAES DE CARVALHO, A. (eds.). Bioelectrogenesis. New York: Elsevier Science, 1961. p. 171–184.