60 - Electrocytes of Electric Fish

Abstract

This chapter discusses the anatomy and cellular morphology that electric fish have evolved for producing powerful electrical discharges. The chapter mentions that the freshwater electric eel (Electrophorus electricus) and the saltwater electric ray (genus Torpedo) produce extraordinarily powerful electrical discharges with membrane ion channels, receptors, and pumps common to other excitable cells. It is mentioned that the powerful electrical discharges can be measured in the water surrounding these animals. The chapter discusses several related concepts, including anatomy of Electrophorus and mechanism of the electrical discharge, electrocyte membrane electrophysiology, and comparative physiology of Electrophorus and Torpedo with models for mammalian excitable cells. The membrane receptors, ion channels, and ATPases responsible for electric tissue electrophysiology are biochemically and functionally identical to those of mammalian muscle and nerve. Powerful electric fish possess a specialized anatomy and cellular morphology devoted to the production of electrical discharges. Electromotor neurons radiate into the electric organ, innervating individual electrocytes. Electrocytes of both the main electric organ and Sach's organ are large ribbon-shaped cells. Electrocyte membranes contain many of the same protein elements found in myocytes and neurons. Calmodulin is present throughout the cytoplasm of electrocytes, but is particularly concentrated near both the innervated and non-innervated membranes. The marine electric ray (genus Torpedo and various species—marmorata, californica, nobilianae, occidentalis) can produce high-amperage electrical discharges by virtue of numerous electrocyte columns arranged in parallel. The membrane potentials used by electrocytes to produce transcellular potentials are remarkably similar to those of other excitable cells, such as myocytes and neurons. Currents that give rise to electrocyte membrane potentials can even be represented by equivalent circuits similar to those of other excitable cells.