MICROVILLI IN ELECTRORECEPTOR ORGANS IN ICTALURUS-NEBULOSUS PLAY A PART IN SIGNAL FILTERING

Ampullary electroreceptor organs of catfish show a band-pass-filter ch aracteristic on sinusoidal electric stimulation. The structures and pr ocesses which are responsible for the frequency characteristics are no t fully understood. To investigate the role of the apical membrane and its microvilli in signal filtering, the ampullary organs were apicall y exposed to the actin filament disrupting agent cytochalasin B. Elect rophysiological data showed that cytochalasin B treatment reduced the absolute sensitivity to about 20% over the whole frequency range. The decrease in sensitivity at 20 Hz, however, was less than at other freq uencies. The phase lags at 14 and 20 Hz became less negative, indicati ng a relatively better transduction at high frequencies. Calculations with an electric equivalent circuit of an electroreceptor cell indicat ed that a reduction in apical surface area in combination with a reduc tion of the number or the conductivity of apical ion channels can expl ain such effects. We conclude that, although only the basal membrane i s thought to be involved in stimulus transduction, the apical membrane contributes considerably to the frequency characteristics of ampullar y electroreceptor organs.