Calcium adenylyl cyclase regulation

Clark MJ, Harrison C, Zhong H, et al Endogenous RGS protein action modulates mu-opioid signaling through Galphao effects on adenylyl cyclase, extracellular signal-regulated kinases, and intracellular calcium pathways. J Biol Chem 278 9418-9425, 2003... 

Autonomic receptors further regulate calcium influx through the sarcolemma (Fig. 15.1). (3-Adrenergic stimulation results in the association of a catalytic subunit of a G protein coupled to the (3-receptor. This stimulates the enzyme adenylyl cyclase to convert ATP to cyclic adenosine monophosphate (cAMP). Increasing cAMP production results in a cAMP-dependent phosphorylation of the L-type calcium channel and a subsequent increase in the probability of the open state of the channel. This translates to an increase in transsarcolemmal calcium influx during phase 2 (the plateau phase) of the cardiac muscle action potential. The effects of transient increases in intracellular levels of cAMP are tightly con-... 

Plasma calcium concentration is the principal factor regulating PTH synthesis and release. The increase in PTH synthesis and secretion induced by hypocalcemia is believed to be mediated through activation of parathyroid gland adenylyl cyclase and a subsequent increase in intracellular cyclic adenosine monophosphate (cAMP). 

Nucleotide Cyclases. Calmodulin regulates the activity of different nucleotide cyclases such as adenylyl cyclase that catalyzes the formation of cAMP from ATP. cAMP is another important molecule in the cell functioning as a second-messenger like calcium. The cahnodulin-adenylyl cyclase interaction links these two second messengers together. ... 

The H2 receptor is a 359-amino-acid protein in humans. It has some features similar to the Hi protein (e.g., N-terminal glycosylation sites) and phosphorylation sites in the C-terminal. An aspartic acid residue in the third transmembrane loop appears to be critical to agonist and antagonist binding, and threonine/aspartate and tyrosine/aspartate couples in the fifth transmembrane domain appear to be important for interaction of the imidazole part of the histamine molecule. It is positively coupled via Gas to activate adenylyl cyclase for synthesis of cyclic adenosine monophosphate (cAMP) as a second messenger. In some systems, it is coupled through Gq proteins to stimulate phospholipase C. It appears in some cells that other processes, such as breakdown of phosphoinositides, control of intracellular calcium ion levels, and phospholipase A2 activity, can be regulated by other cAMP-independent pathways. 

---