The effects of dopamine and dopamine receptor agonists on the phototransduction cascade of frog rods.

Abstract

Dopamine induces a decrease in rod sensitivity, mostly by reducing the activation rate of the cascade, and to a much lesser extent, speeding up the turning off of the cascade. The sign of the reaction to all tested drugs, lack of selectivity of dopamine and dopamine receptor agonist action, and analysis of factors that determine sensitivity of photoreceptors suggest that, in rod outer segments (ROSs), dopamine action is mediated by D₁-D₂ receptor heterodimers but not D₁R or D₂R alone. This work supports the assumption made earlier by other authors that dopamine exercises its regulatory effect via at least two independent mechanisms, which are cAMP and Ca²⁺ mediated.