Injection of guanosine and adenosine nucleotides into Limulusventral photoreceptor cells

1. Several nucleotide and nucleotide analogues had striking effects when pressure‐injected into Limulusventral photoreceptor cells. The poorly hydrolysable GTP analogues guanosine 5′‐0‐(3‐thiotriphosphate) (GTPγS), guanylyl imidodiphosphate (Gpp[NH]p) and guanylyl (β, γ methylene) diphosphonate (Gpp[CH2]p) produced large increases in the frequency of ‘discrete events’ that were recorded from photoreceptors in darkness. This effect was only observed after the injected cell was exposed to light. Injection of the ATP analogue ATPγS had effects similar to those of the GTP analogues.