Daily cycle influences how dopamine controls light-sensitive channels in cone cells

Dopamine (DA) and D2 receptor agonists may shift the affinity of cGMP-gated ion channels in chick retinal cone photoreceptors based on the time of day.

• Dopamine and D2 agonists significantly increased the K(D) for cGMP during the night (circadian time 16-19) but not during the day (circadian time 4-7).
• A brief exposure to DA or quinpirole decreased K(D) during the subjective day and had no effect during the subjective night.
• The effect of D2 agonists on K(D) is associated with both the duration of exposure and the circadian timing.
• DA treatment activated the MAP kinase Erk during the day but inhibited it at night.
• D2 agonists activated Ca2+/calmodulin-dependent protein kinase II during the night and inhibited it during the day.

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