THE NUCLEOTIDE CONTENT OF THE OCTOPUS PHOTORECEPTOR CELLS - NO CHANGES IN THE OCTOPUS RETINA IMMEDIATELY FOLLOWING AN INTENSE LIGHT FLASH

The amounts of cyclic-guanosine monophosphate (cGMP) and cyclic-adenos ine monophosphate (cAMP) in octopus retina were measured by competitiv e radioimmunoassay. The amounts of the respective di- and tri-phosphon ucleotides, and of visual pigment (as retinal isomers), were determine d by high-performance-liquid chromatography (HPLC). Unirradiated octop us retina contained 2.4+/-0.5 pmol of cGMP and 36+/-7.0 pmol of cAMP. When 27.6% of the visual pigment in the retina was converted into the meta-form by an intense light flash, the rapidly-frozen retina contain ed 2.3+/-0.9 pmol of cGMP and 32+/-4.0 pmol of cAMP: no significant ch anges from the unirradiated state. The molecular ratios of cGMP and cA MP to total visual pigment were estimated to be 1/1800 and 1/120, resp ectively. Assuming that all the cGMP and cAMP were contained only in t he rhabdome, it was estimated that there are 1.6 molecules of cGMP and 24 molecules of cAMP per microvillus. The low content of cGMP in the microvillus and the absence of significant change in cGMP content on e xposure to light lead us to conclude that cGMP is not the 'intracellul ar messenger' of phototransduction in octopus photoreceptor cells.