M. Seidou et al., THE NUCLEOTIDE CONTENT OF THE OCTOPUS PHOTORECEPTOR CELLS - NO CHANGES IN THE OCTOPUS RETINA IMMEDIATELY FOLLOWING AN INTENSE LIGHT FLASH, Zoological science, 10(2), 1993, pp. 275-279
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.