Muscarinic-dopaminergic synergism on retinal cyclic AMP formation

The cholinergic agonist, carbachol, produces a small increase in cyclic AMP concentration in the isolated rat retina, and markedly potentiates dopamine-stimulated cyclic AMP formation. This effect of carbachol is mediated through a muscarinic receptor, is calcium-independent, and is not due to inhibition of phosphodiesterase activity. Activation of muscarinic receptors may potentiate dopaminergic responses in the retina by enhancing coupling of the dopamine receptor to adenylate cyclase.