Cyclic adenosine monophosphate signal transduction

Figure 14-2. Principles of biological transduction and amplification. Binding of an effector at a receptor protein R induces a conformation change which can directly have for consequence the opening of an ion channel (left) with electrolyte influx and membrane depolarization, or initiate the formation of a second messenger (here cyclic adenosine monophosphate, cAMP) by adenylate cyclase, which can then, in catalytic amplification steps, lead to electrochemical or chemical ampliflcation and signal spreading.

Luteinizing hormone binds to its receptor on the surface of the Leydig cells to initiate testosterone biosynthesis. As in other endocrine cells, the binding of gonadotropin activates the Gs signal transduction pathway, increasing intracellular cyclic adenosine monophosphate (cAMP) levels via activation of adenylate cyclase. One of the processes influenced by elevated cAMP levels is the... 

The receptors for sweetness and bitterness act via cell-surface receptors linked to intracellular formation second messengers. There is evidence that both cyclic adenosine monophosphate (cAMP) (section 1.3.2) and inositol trisphosphate (section 10.3.3) mechanisms are involved, and more than one signal transduction pathway may be involved in the responses to sweetness or sourness of different compounds. Some compounds may activate more than one type of receptor. 

Cyclic adenosine monophosphate is an important intracellular second messenger which relays signals from the receptors on the ceU surface to target molecules inside the cell, in the cytoplasm or nucleus (signal transduction). Earl Sutherland won the Nobel Prize in Physiology and Medicine in 1971 for this discovery. 

Studies of peripheral NE receptor function have also shown alterations in a2 receptor and cyclic adenosine 39,59-monophosphate (cAMP) function in patients with PTSD. Decreases in platelet adrenergic a2-receptor number (Perry et al. 1987), platelet basal adenosine, isoproterenol, forskohn-stimulated cAMP signal transduction (Lerer et al. 1987), and basal platelet monoamine oxidase (MAO) activity (Davidson et al. 1985) have been found in PTSD. These findings may reflect chronic high levels of NE release which lead to compensatory receptor down-regulation and decreased responsiveness. 

FIGURE 10.9 Structures of some compounds involved in signal transduction, (a) Adenosine 3, 5 -cyclic monophosphate (cyclic AMP, cAMP). (b) Phosphatidylinositol (PI), (c) Phosphatidylinositol 4-phosphate (PIP), (d) Phosphatidylinositol 4,5-bisphosphate (PIPj). (e) 1,2-Diacylglycerol. (0 Inositol trisphosphate (IP3)... 

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