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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 VGCC[alpha]1C and VGCC[alpha]1D subunits, we found that the immunofluorescence intensities of both VGCC[alpha]1C and VGCC[alpha]1D in photoreceptors are higher during the subjective night. However, the mRNA levels of VGCC[alpha]1D, but not VGCC[alpha]1C, 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.

(C) 2007 International Society for Neurochemistry