Dopaminergic mechanisms in the carp retina: Effects of dopamine, K(+) and light on cyclic AMP synthesis.

The ability of dopamine, other proposed retinal transmitters, depolarizing agents, and light to stimulate adenylate cyclase activity in the carp retina has been examined. In both homogenates and pieces of intact tissue, all of the evidence suggests that a dopamine-sensitive adenylate cyclase is the only neurotransmitter activated adenylate cyclase in the carp retina. Experiments involving the use of several dopaminergic agonist and antagonist drugs indicate that this system possesses similar, if not identical pharmacological properties to those reported in various areas of the mammalian central nervous system. Furthermore, binding studies with (3)H-domperidone suggest that all dopamine receptors in the retina are linked to adenylate cyclase, implying that the activation of the retinal dopaminergic neurones increases cyclic AMP levels in all postsynaptic neurones. Depolarizing agents, such as K(+), also appear to increase retinal cyclic AMP levels via dopamine. Evidence is provided that K(+) releases endogenous stores of dopamine through a Co(2+) sensitive mechanism. Finally, flashing lights slightly increase cyclic AMP levels in the retina, an effect that is abolished by haloperidol.