Retinal rod and cone cGMP phosphodiesterases function as theeffector enzymes in the vertebrate visual transduction cascade.This family represents the inhibitory gamma subunit [1], whichis also expressed outside retinal tissues and has been shown tointeract with the G-protein-coupled receptor kinase 2 signallingsystem to regulate the epidermal growth factor- andthrombin-dependent stimulation of p42/p44 mitogen-activatedprotein kinase in human embryonic kidney 293 cells [2].