Cyclic guanosine 3 ,5 -monophosphate second messenger

Inhibition of cyclic nucleotide phosphodiesterases is widely accepted as the predominant mechanism by which theophylline produces bronchodilation. Phosphodiesterases are enzymes that inactivate cAMP and cyclic guanosine monophosphate (GMP), second messengers that mediate bronchial smooth muscle relaxation. 

Activation of the postsynaptic receptor also leads to activation of the enzymes involved m the formation of so-called second messengers (see Box 42 for explanation of this and other terms used m this section). Best-known second messengers are cychc adenosine monophosphate (cAMP), cyclic guanosine monophosphate (cGMP) and cleavage products of phosphatidyh-nositol. These molecules are formed at the cell membrane and migrate into the cell where they affect the activity of other enzymes. 

The activated G-protein subunits detach from the receptor and initiate signalling from many downstream effector proteins, including phosphodiesterases, adenyl cyclase, phosphohpases and ion channels, which permit the release of second messenger molecules such as cychc adenosine monophosphate (cAMP), cyclic guanosine monophosphate (cGMP), inositol triphosphate, diacylglycerol and calcium ions. 

Cyclic guanosine monophosphate (cGMP) is the ubiquitous second messenger for GPCRs activated by endogenous substances such as nitric oxide (NO)... 

For the receptors that bind atrial natriuretic peptides and the peptides guanylin and uroguanylin, the intracellular domain is not a protein kinase but rather a guanylyl cyclase that synthesizes the second messenger cyclic guanosine monophosphate (cyclic GMP), which activates a cyclic GMP-dependent protein kinase (PKG) and can modulate the activities of several cyclic nucleotide phosphodiesterases, among other effectors. 

Second messengers are specific intracellular components that are indirectly stimulated by the first messengers to activate intracellular components such as certain enzymes termed protein kinases (PKs). The most studied second messengers are calcium ion, inositol trisphosphate (IP3), diacylglycerol (DAG), cyclic adenosine monophosphate (cAMP), and cyclic guanosine monophosphate (cGMP). 

There is a wide range of indirect indices for NO production. These are most commonly used for the investigation of NO in biological systems. They do not have the specificity of direct measurements, but they are more convenient. They include NO metabolites, the second messenger cyclic guanosine monophosphate (cGMP), and effector organ responses such as vessel dilation and platelet function. 

The activation of the calcium second messenger system by hormones, neurotransmitters, iocal mediators, and sensory stimuii is very important in reguiating VSM contraction. Severai signai transduction mechanisms modulate intracellular calcium concentration and, therefore, the state of vascular tone. These calcium second messenger systems are the phosphatidyiinositol (PIP2)/Gq protein-coupled pathway, the cyclic adenosine monophosphate (cAMP)/Gs protein-coupied pathway, and the NO/cyclic guanosine monophosphate (cGMP) pathway. 

Cyclic GMP. Cyclic guanosine monophosphate, c-GMP, (11.86b) is a second messenger which plays an important role in retinal visual processes. 

Cyclic nucleotides, 3, 5 -cyclic adenosine monophosphate (cAMP) and 3, 5 -cyclic guanosine monophosphate (cGMP), function to regulate cell-to-cell communication processes (33). Cellular communication follows primarily three pathways. The first involves the transmission of electrical impulses via the nervous system. The second involves chemical messengers or hormonal secretions. The third involves de novo protein synthesis. All three processes are usually in response to some demand or stimulus and involve, at least to some extent, regulation by cyclic nucleotides ... 

The enzyme guanylyl cyclase produces the second messenger guanosine monophosphate (3, 5 -cyclic GMP, cGMP) from guanosine triphosphate (GTP). 

The most common second messenger activated by protein/peptide hormones and catecholamines is cyclic adenosine monophosphate (cAMP). The pathway by which cAMP is formed and alters cellular function is illustrated in Figure 10.1. The process begins when the hormone binds to its receptor. These receptors are quite large and span the plasma membrane. On the cytoplasmic surface of the membrane, the receptor is associated with a G protein that serves as the transducer molecule. In other words, the G protein acts as an intermediary between the receptor and the second messengers that will alter cellular activity. These proteins are referred to as G proteins because they bind with guanosine nucleotides. In an unstimulated cell, the inactive G protein binds guanosine diphosphate (GDP). When the hormone... 

The cyclic nucleotides adenosine 3, 5 -cyclic monophosphate (cyclic AMP (cAMP)) and guanosine 3, 5 -cyc.lic monophosphate (cyclic GMP (c.GMP)) are second messengers generated by adenylyl (adenylate) cyclase (AC) and guanylyl (guanylate) cyclase (GC), respectively, in response to receptor occupation by particular primary messengers , that is,... 

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