Acetylcholine adenylyl cyclase inhibition

In GH cells SST inhibits prolactin secretion induced by cAMP analogs and K+-induced depolarization in addition to inhibiting adenylyl cyclase activity [192], Similar data were also obtained with ACTH-secreting AtT-20 cells [203]. PTX blocks SST inhibition of ligand-induced and cAMP analog-induced secretions in both GH and AtT-20 cells [106,107]. Thus, it is clear that a G protein is involved in both the cAMP dependent and the cAMP-independent actions of SST. Quin-2 measurements showed that exposure of cells to SST lowers the intracellular Ca2+ levels. This effect is also PTX-sensitive [211-213], The decline in intracellular Ca2+ was concluded to be secondary to SST hyperpolarizing the cells by increasing K+ conductance [214,215]. Acetylcholine, like SST, causes inhibition of adenylyl cyclase, hy-... 

Acetylcholine has two types of receptors nicotinic ion channel receptors, the receptors inhibited by antibodies in myasthenia gravis, and muscarinic receptors, which exist as a variety of subtypes. The M2 muscarinic receptors activate a Gai/ het-erotrimeric G protein in which release of the Py subunit controls K+ channels and pacemaker activity in the heart. Epinephrine has several types and subtypes of heptahelical receptors p receptors work through a Ga and stimulate adenylyl cyclase 2 receptors in other cells work through a G i protein and inhibit adenylyl cyclase receptors work through Ga, subunits and activate phospholipase Cp. This variety in receptor types allows a messenger to have different actions in different cells. 

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