Vanadate, tungstate and molybdate activate rod outer segment phosphodiesterase in the dark

Anionic activation of rod outer segment phosphodiesterase by vanadate, molybdate and tungstate is demonstrated. Comparisons are made to adenylate cyclase, which is known to be activated by vanadate and molybdate but not by tungstate. In view of the differences in anionic activation between these two important enzymatic regulators of intracellular cyclic nucleotide metabolism, it is possible that tungstate can be used as a selective probe for the effects of phosphodiesterase activity in photoreceptors and other cells. The known electrophysiological stimulation of Limulus photoreceptors by these anions is also interpreted in light of our results. If anionic production of quantum bumps in Limulus photoreceptors is mediated by changes in cyclic nucleotides, then the electrophysiological response of Limulus photoreceptors to tungstate may indicate a role for phosphodiesterase rather than adenylate cyclase in mediating light-induced cyclic nucleotide alterations in this cell.