Excitation of Limulus Photoreceptors by Hydrolysis-Resistant Analogs of cGMP and cAMP
Limulus polyphemus, Photoreceptor, Cyclic guanosine 5′-phosphate, Cyclic adenosine 5′-phosphate
cGMP was proposed to be the agent which directly opens the light-sensitive channel in Limulus ventral photoreceptors. However, the light-sensitive rhabdomeral-lobe (R-lobe) is not uniformly responsive to cGMP injection; that is, there are ‘hot spots’ of sensitivity. A potent phosphodiesterase which rapidly hydrolyses cGMP was suggested to explain the existence of these ‘hot spots’. To test this idea we injected ventral photoreceptors with hydrolysis-resistant cyclic nucleotide analogues. Whereas there can be a lack of a response to cGMP injection into the R-lobe, we find a reproducible depolarization upon R-lobe injection of hydrolysis-resistant cGMP analogues. Furthermore, the depolarization resulting from the injection of cGMP analogues does not require a rise in intracellular Ca2+, as it is not blocked by the Ca2+ buffer, BAPTA. Surprisingly, R-lobe injection of a hydrolysis-resistant cAMP analogue also depolarized ventral photoreceptors. Further work will be needed to resolve the role of cGMP in Limulus visual transduction.
Jane M. Feng, Tamara M. Frank, and Alan Fein. 1991. Excitation of Limulus Photoreceptors by Hydrolysis-Resistant Analogs of cGMP and cAMP .Brain Research , (2) : 291 -294. https://nsuworks.nova.edu/occ_facarticles/766.