The expression of L-type voltage-gated calcium channels in retinal photoreceptors is under circadian control

Authors

  • Michael L. Ko,

    1. Department of Veterinary Integrative Biosciences, College of Veterinary Medicine and Biomedical Sciences, Texas A&M University, College Station, Texas, USA
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  • Yilin Liu,

    1. Department of Veterinary Integrative Biosciences, College of Veterinary Medicine and Biomedical Sciences, Texas A&M University, College Station, Texas, USA
    2. Department of Biology, Texas A&M University, College Station, Texas, USA
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  • Stuart E. Dryer,

    1. Department of Biology and Biochemistry, University of Houston, Houston, Texas, USA
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  • Gladys Y.-P. Ko

    1. Department of Veterinary Integrative Biosciences, College of Veterinary Medicine and Biomedical Sciences, Texas A&M University, College Station, Texas, USA
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Address correspondence and reprint requests to Gladys Y.-P. Ko, PhD, Department of Veterinary Integrative Biosciences, College of Veterinary Medicine and Biomedical Sciences, Texas A&M University, mail stop 4458, College Station, TX 77843-4458, USA.
E-mail: gko@cvm.tamu.edu

Abstract

Photoreceptors are non-spiking neurons, and their synapses mediate the continuous release of neurotransmitters under the control of L-type voltage-gated calcium channels (VGCCs). Photoreceptors express endogenous circadian oscillators that play important roles in regulating photoreceptor physiology and function. Here, we report that the L-type VGCCs in chick cone photoreceptors are under circadian control. The L-type VGCC currents are greater when measured during the subjective night than during the subjective day. Using antibodies against the VGCCα1C and VGCCα1D subunits, we found that the immunofluorescence intensities of both VGCCα1C and VGCCα1D in photoreceptors are higher during the subjective night. However, the mRNA levels of VGCCα1D, but not VGCCα1C, are rhythmic. Nocturnal increases in L-type VGCCs are blocked by manumycin A, PD98059, and KN93, which suggest that the circadian output pathway includes Ras, Erk, and calcium-calmodulin dependent kinase II. In summary, four independent lines of evidence show that the L-VGCCs in cone photoreceptors are under circadian control.

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