the high affinity choline transporter (hacht) activity is considered to be the rate-limiting step in acetylcholine (ach) synthesis in the cholinergic terminal. recent studies show that hacht contains consensus serine and threonine residues for protein kinase a (pka) phosphorylation. using chick retinal neurons evaluated the effects of the second messenger camp on the hacht activity. the increase of the intracellular camp levels through phosphodiesterase inhibition, adenilatecyclase activation or using a phosphodiesterase-resistant camp analog decreased hacht activity between 29 and 69%. moreover, the activation of dopamine d1-type receptors increase the intracellular camp levels and activates pka, however, the treatment with dopamine d1 or d2 receptor antagonists does not induce changes on transporter activity.