RECEPTOR POTENTIAL OF RETINULAR CELLS OF THE BLOWFLY CALLIPHORA - ROLE OF SODIUM, POTASSIUM AND CALCIUM-IONS

Simultaneous membrane potential and membrane resistance measurements and current clamp experiments were performed on the visual sense cells of Calliphora. 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 of Calliphora 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. © 1979 Springer-Verlag.