It is assumed that cyclic nucleotides are involved in signal transduction of invertebrate photoreceptors. In this study, membranes of photoreceptor cells from freshly caught cuttlefish were isolated, and the membrane proteins were reconstituted into proteoliposomes. With the dye Neutral red it was possible to measure cyclic nucleotide induced Na+ fluxes into the liposomes. cGMP and cAMP concentrations for half maximal activation of Na+ fluxes are 77 μM and 224 μM, respectively, with Hill coefficients of 2.0 for cGMP and 2.4 for cAMP. These fluxes may demonstrate the presence of at least one cyclic nucleotide gated cation channel in the membranes of the photoreceptor cells of the invertebrateSepia officinalis.
