Interpretation of invertebrate photoreceptor potentials in terms of a quantitative model

It is known from voltage-clamp experiments on visual cells of Limulus and Balanus that the total membrane current can be separated approximately into a dark current JD and a light-induced current JL such that each part has a time-and intensity-independent reversal potential. In addition JL can be represented approximately as a product of a nonlinear, time independent current-voltage characteristics J0L (v) and an "activation factor" xa which depends on light intensity and time. J0L(V) can be described by a simple electro-diffusion membrane model (for JD we use the same model). A set of kinetic equations including amplification, latency and light adaptation leads to a determination of xa for photoisomerization of single rhodospin molecules and for arbitrary light signals. The receptor potentials calculated show many features of the experiments on Limulus, Balanus and Astacus.