Cyclic nucleotides and inositol trisphosphate activate different components of the receptor current in Limulus ventral nerve photoreceptors.

Receptor currents activated by short flashes were measured in ventral nerve photoreceptors of Limulus before and after injection of neomycin or phosphodiesterase (PDE). Neomycin inhibits the inositol cascade and PDE hydrolyses cyclic nucleotides. The effect of these substances was studied on the three current components, which were suggested to be activated by distinct transduction mechanisms. The second component of the current was selectively blocked by neomycin and the third component by PDE. The first component was inhibited by both substances. Thus, two transduction mechanisms for two current components could be unequivocally identified. Results support the previous assumption that light activates distinct mechanisms and transmitters in Limulus photoreceptors.