title: Phosphatidylinositol 3 kinase-Akt signaling serves as a circadian output in the retina.
abstract: The daily rhythm of L-type voltage-gated calcium channels (L-VGCCs) is part of the cellular mechanism underlying the circadian regulation of retina physiology and function. However, it is not completely understood how the circadian clock regulates L-VGCC current amplitudes without affecting channel gating properties. The phosphatidylinositol 3 kinase-protein kinase B (PI3K-Akt) signaling pathway has been implicated in many vital cellular functions especially in trophic factor-induced ion channel trafficking and membrane insertion. Here, we report that PI3K-Akt signaling participates in the circadian phase-dependent modulation of L-VGCCs. We found that there was a circadian regulation of Akt phosphorylation on Thr308 that peaked at night. Inhibition of PI3K or Akt significantly decreased L-VGCC current amplitudes and the expression of membrane-bound L-VGCCalpha1D subunit only at night but not during the subjective day. Photoreceptors transfected with a dominant negative Ras had significantly less expression of phosphorylated Akt and L-VGCCalpha1D subunit compared with non-transfected photoreceptors. Interestingly, both PI3K-Akt and extracellular signal-related kinase were downstream of Ras, and they appeared to be parallel and equally important pathways to regulate L-VGCC rhythms. Inhibition of either pathway abolished the L-VGCC rhythm indicating that there were multiple mechanisms involved in the circadian regulation of L-VGCC rhythms in retina photoreceptors.
authors.affiliation: Department of Veterinary Integrative Biosciences, College of Veterinary Medicine and Biomedical Sciences, Texas A&M University, College Station, Texas, USA.
authors.forename: Michael L
authors.initials: ML
authors.lastname: Ko
authors.forename: Kuihuan
authors.initials: K
authors.lastname: Jian
authors.forename: Liheng
authors.initials: L
authors.lastname: Shi
authors.forename: Gladys Y-P
authors.initials: GY
authors.lastname: Ko
mesh_terms: D000818:Animals; D055592:Biophysical Phenomena / Q000502:physiology; D019921:Biotinylation; D020746:Calcium Channels, L-Type / Q000502:physiology; D002478:Cells, Cultured; D002642:Chick Embryo; D002940:Circadian Rhythm / Q000502:physiology*; D004558:Electric Stimulation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005786:Gene Expression Regulation / Q000187:drug effects / Q000502:physiology; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D051058:Oncogene Protein v-akt / Q000378:metabolism*; D018408:Patch-Clamp Techniques / Q000379:methods; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D021381:Protein Transport / Q000187:drug effects / Q000502:physiology; D012160:Retina / Q000187:drug effects / Q000502:physiology*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D014162:Transfection
chemical_list: D020746:Calcium Channels, L-Type; D004791:Enzyme Inhibitors; D019869:Phosphatidylinositol 3-Kinases; D051058:Oncogene Protein v-akt