Photoreceptors of the retina and pinealocytes of the pineal gland share common components of signal transduction.
Light absorbed by retinal photoreceptors triggers a cascade of reactions that initiate cGMP hydrolysis, cation channel closure and membrane hyperpolarization. Down-regulation of the cascade involves additional proteins that interfere with amplification along the cascade. Pinealocytes are activated by norepinephrine during the dark phase of the day/night cycle. Mature pinealocytes of the mammalian pineal express the known photoreceptor proteins that are implicated in down-regulation of the visual cascade, but the cascade components that produce cGMP hydrolysis and membrane hyperpolarization are absent. Pinealocytes accumulate cyclic AMP minimally when norepinephrine activates their beta adrenergic receptors alone, but the response is potentiated by the simultaneous activation of their alpha-1 adrenergic receptors. A model is proposed whereby phosducin, a phosphoprotein that binds the beta,gamma subunit of G-proteins, could modulate the synthesis of cyclic AMP by buffering the amount of beta,gamma G-protein subunits that are available for activating adenylate cyclase.
Lolley
R N
RN
Department of Anatomy and Cell Biology, UCLA School of Medicine 90024.
Craft
C M
CM
Lee
R H
RH
D000818:Animals; D005136:Eye Proteins / Q000737:chemistry / Q000502:physiology; D020555:GTP-Binding Protein Regulators; D019204:GTP-Binding Proteins / Q000378:metabolism; D008550:Melatonin / Q000096:biosynthesis; D009638:Norepinephrine / Q000494:pharmacology; D010750:Phosphoproteins / Q000737:chemistry / Q000502:physiology; D010786:Photoreceptor Cells / Q000502:physiology*; D010870:Pineal Gland / Q000187:drug effects / Q000502:physiology*; D012160:Retina / Q000502:physiology*; D015398:Signal Transduction / Q000502:physiology*
D005136:Eye Proteins; D020555:GTP-Binding Protein Regulators; D010750:Phosphoproteins; C065631:phosducin; D019204:GTP-Binding Proteins; D008550:Melatonin; D009638:Norepinephrine