Isolated from the Indian plant Coleus barbatus (formerly Plectranthus forskohlii), forskolin is a cell-permeable labdane diterpene containing a characteristic tetrahydropyran-derived heterocyclic ring.
Forskolin binds directly in the catalytic cleft between the C1 and C2 cytoplasmic domains of transmembrane adenylyl cyclases (AC1–AC8, sparing AC9 and soluble AC), raising intracellular cyclic AMP (cAMP) independently of cell-surface Gs-coupled GPCRs.
In GPCR pharmacology, a submaximal concentration of forskolin is routinely applied so Gi/o-coupled receptor agonists can be assayed by their ability to inhibit forskolin-stimulated cAMP accumulation.