An unusual cGMP pathway underlying depolarizing light response of the vertebrate parietal-eye photoreceptor.
All cellular signaling pathways currently known to elevate cGMP involve the activation of a guanylyl cyclase to synthesize cGMP. Here we describe an exception to this rule. In the vertebrate parietal eye, the photoreceptors depolarize to light under dark-adapted conditions, unlike rods and cones but like most invertebrate photoreceptors. We report that the signaling pathway for this response involves a rise in intracellular cGMP resulting from an inhibition of the phosphodiesterase that hydrolyzes cGMP. Furthermore, this phosphodiesterase is driven by an active G protein in darkness. These results indicate an antagonistic control of the phosphodiesterase by two G proteins, analogous to the Gs/Gi control of adenylyl cyclase. Our findings demonstrate an unusual phototransduction mechanism and at the same time indicate that signaling involving cyclic nucleotides is more elaborate than previously known.
Xiong
W H
WH
Howard Hughes Medical Institute, Baltimore, Maryland, USA.
Solessio
E C
EC
Yau
K W
KW
D000818:Animals; D006152:Cyclic GMP / Q000378:metabolism* / Q000528:radiation effects; D003623:Dark Adaptation / Q000502:physiology; D004594:Electrophysiology; D019204:GTP-Binding Proteins / Q000502:physiology; D006868:Hydrolysis; D008027:Light; D008116:Lizards / Q000502:physiology*; D009799:Ocular Physiological Phenomena; D010727:Phosphoric Diester Hydrolases / Q000378:metabolism; D010786:Photoreceptor Cells / Q000502:physiology* / Q000528:radiation effects*
D010727:Phosphoric Diester Hydrolases; D019204:GTP-Binding Proteins; D006152:Cyclic GMP