Cyclic GMP in lateral eyes of the horseshoe crab Limulus

In Limulus photoreceptors, light induces a depolarization. The gating mecha nism of the cation channels involved is not understood but evidence exists that cyclic nucleotides may act as ligands. Using an antiserum against a cG MP-protein conjugate, we found strong immunoreactivity localized to the lig ht-sensitive rhabdoms of lateral eye photoreceptors. In homogenated tissue, the cGMP concentration was on average 0.2 pmol/mg retinal tissue protein b oth in light- and dark-adapted eyes. Phosphodiesterase inhibitors caused a 2-3-fold increase in the cGMP level. Despite our failure to detect a light dependence of the cGMP concentration, these results support the proposed ro le of cGMP in Limulus phototransduction. (C) 2000 Elsevier Science Ltd. All rights reserved.