The cyclic AMP pathway.

Cyclic adenosine 3′,5′-monophosphate (cAMP) was the first second messenger to be identified and plays fundamental roles in cellular responses to many hormones and neurotransmitters (Sutherland and Rall 1958). The intracellular levels of cAMP are regulated by the balance between the activities of two enzymes (see Fig. 1): adenylyl cyclase (AC) and cyclic nucleotide phosphodiesterase (PDE). Different isoforms of these enzymes are encoded by a large