D2 dopamine receptors and cAMP differently affect calcium signals in rod and cone cells of tiger salamander retina

Dopamine and a D2 agonist enhanced L-type calcium currents in rods and small single cones but inhibited them in large single cones.

• Dopamine and quinpirole increased calcium currents in specific photoreceptor types while decreasing them in others.
• A D1 agonist did not affect calcium currents in any of the photoreceptors tested.
• The effects of quinpirole were dependent on PTx-sensitive G-proteins, indicating a specific signaling pathway.
• Inhibition of a protein kinase associated with cAMP enhanced calcium currents in rods and small cones but inhibited them in large cones.
• Stimulation of protein kinase activity had opposite effects, suggesting complex regulatory mechanisms within different cone types.
• Findings challenge previous assumptions about dopamine's role in modulating photoreceptor inputs to second-order neurons.

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