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Sensitive Assays for Cyclic Nucleotide Signaling

Cyclic adenosine monophosphate (cyclic AMP or cAMP) and cyclic guanosine monophosphate (cyclic GMP or cGMP) are prolific intracellular signaling molecules. cAMP is synthesized from adenosine triphosphate (ATP) by the enzyme adenylyl cyclase (AC) and used for intracellular signal transduction in many different organisms.

Adenylyl cyclase (AC) is located on the inner surface of the cellular lipid bilayer. AC is activated by a range of signaling molecules through the activation of AC stimulatory G (Gs)-protein-coupled receptors, and inhibited by agonists of AC inhibitory G (Gi)-protein-coupled receptors. Variation in the expression of these receptors allows AC activity to be very responsively controlled in different tissue types.  For example, liver AC activity is more strongly upregulated by extracellular glucagons, while muscle AC reacts more strongly to adrenaline. cAMP decomposition into AMP is catalyzed by phosphodiesterase enzymes. cAMP is involved in the activation of protein kinases and regulates the phosphorylation of a variety of substrates. Recent research suggests that cAMP also affects the function of higher-order thinking in the prefrontal cortex through its regulation of ion channels called hyperpolarization-activated cyclic nucleotide-gated (HCN) channels.

cGMP synthesis is similarly catalyzed by guanylate cyclase (GC), which converts GTP to cGMP. GC is activated by a different set of peptide hormones, including atrial natriuretic factor, while soluble GC is typically activated by nitric oxide to stimulate cGMP synthesis. cGMP is a common regulator of ion channel conductance, glycogenolysis, and cellular apoptosis. It also relaxes smooth muscle tissues, and in blood vessels, relaxation of vascular smooth muscles leads to vasodilation and increased blood flow.

The first immunoassays for cyclic nucleotides were published in the early 1970’s, and the introduction of commercially available radioactively labeled cAMP and cGMP allowed the measurement of cyclic AMP and GMP at lower and lower concentrations. Most RIAs for cAMP and cGMP have been replaced by colorimetric, fluorescent, and now, chemiluminescent immunoassays. The advent of direct assays for cAMP and cGMP, which allow the cyclic nucleotides to be measured in cells and tissues without the need for lengthy pretreatment steps, now allows the measurement of femtomoles of these molecules in just a few hours.

The Arbor Assays cAMP Colorimetric EIA (K019-H) and Chemiluminescent CLIA (K019-C) assay kits, and  cGMP Colorimetric EIA (K020-H) and Chemiluminescent CLIA (K020-C) assay kits, allow for simple, rapid determination of cAMP or cGMP in tissues, cells, saliva, urine, plasma or culture media. Our Chemiluminescent kits are the most sensitive methods available for measuring these molecules. They are ideal for low concentrations of cAMP or cGMP, and when only minute amounts of sample are available.  For research use only. Not for use in diagnostic procedures.

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