Electric Organs

Electric organs are specialized for the production of an electric field outside the body. The study of electric organs and electrocytes has illuminated many aspects of membrane physiology. They are found only in fish but apparently have evolved independently in some six different groups. Their primary usefulness is a result of evolution that has exaggerated different membrane functions in different electrocytes. For example, the concept of independent sites that pass different ions or groups of ions becomes more reasonable given that specific kinds of permeability can occur in isolation in different regions of a single cell or in different cells. Examples are the isolated occurrence of membrane generating postsynaptic potentials (in Astroscopus and torpedinids), of membrane exhibiting delayed rectification, and of the electrically excitable sodium system without delayed rectification (in the electric eel). This macroscopic separation suggests microscopic separation, which in many single membranes can only be inferred from functional arguments or pharmacological data. These specializations of different kinds of membrane cannot really be said to have been responsible for major advances in electrophysiological knowledge. As new morphological, biochemical, and biophysical techniques become available, electrocytes may provide the best tissues for their evaluation.