ELECTRORECEPTOR MODEL OF THE WEAKLY ELECTRIC FISH GNATHONEMUS-PETERSII - I - THE MODEL AND THE ORIGIN OF DIFFERENCES BETWEEN A-RECEPTORS AND B-RECEPTORS

We present an electroreceptor model of the A- and B-receptors of the w eakly electric fish Gnathonemus petersii. The model consists of a sens ory-cell, whose membrane is separated into an apical and basal portion s by support cells, and an afferent fiber. The apical membrane of the cell contains only leak channels, while the basal membrane contains vo ltage-sensitive Ca2+ channels, voltage-sensitive and Ca2+-activated K channels, and leak channels. The afferent fiber is described with the modified Hodgkin;Huxley equation, in which the voltage-sensitive gate of the K+ channels is a dynamic variable; in our model we suggest tha t the electroreceptors detect and process the information provided by an electric organ discharge (EOD) as follows: the current caused by an EOD stimulus depolarizes the basal membrane to a greatly depolarized state. Then the release of transmitter excites the afferent fiber to o scillate after a certain time interval. Due to the resistance-capacita nce structure of the cells, they not only perceive the EOD intensity, but also sense the variation of the EOD waveform, which can be strongl y distorted by the capacitive component of an object. Because of the d ifferent morphologies of A- and B-cells, as well as the different cond uctance of leak ion channels in the apical membrane and the different capacitance of A- and B-cells, A-receptors mainly respond to the EOD i ntensity, while B-receptors are sensitive to the variation of EOD wave form.