At least nine closely related isoforms of adenylyl cyclases (ACs), the enzymes responsible
for the synthesis of cyclic AMP (cAMP) from ATP, have been cloned and characterized in
mammals. Depending on the properties and the relative levels of the isoforms expressed in
a tissue or a cell type at a specific time, extracellular signals received through the G-protein-
coupled receptors can be differentially integrated. The present review deals with various
aspects of such regulations, emphasizing the role of calcium/calmodulin in activating AC1 …