A large number of hormones, neurotransmitters and other signal substances utilize cyclic adenosine 3 5 cyclic monophosphate (cAMP) as an intracellular second messenger. Cyclic AMP regulates a number of different cellular processes such as cell growth and differentiation, ion channel conductivity, synaptic release of neurotransmitters, and gene transcription The principle intracellular target for cAMP in mammalian cells is the cAMP-dependent protein kinase (PKA). The fact that this broad specificity protein kinase mediates a number of discrete physiological responses following cAMP engagement, has raised the question of how specificity is maintained in the cAMP/PKA system. Here, we will describe features of PKA signaling pathway that may contribute to explain how differential effects of cAMP may be maintained in this pathway.