The receptor potential of retinular cells of the blowflyCalliphora: The role of sodium,potassium and calcium ions

Summary Simultaneous membrane potential and membrane resistance measurements and current clamp experiments were performed on the visual sense cells ofCalliphora. The results suggest that the receptor potential is due to two different conductance variations: (i) a conductance increase for both Na⁺- and K⁺-ions upon illumination, and (ii) a light-independent conductance increase for K⁺-ions. Evidence is obtained that in the visual sense cells ofCalliphora the light-independent conductance increase is mediated by the influx of Ca²⁺-ions.The conclusion is that the increase of the intracellular Ca²⁺-ion concentration not only decreases the light-induced conductance, but also increases the light-independent conductance. So the potential of the sense cell is governed by two antagonistic conductances. The functional advantages of such a system are discussed.