CAMP, Dibutyryl

Of the above four factors, epinephrine is the most potent (EC50 = 5 nM), elevating the corneal Isc within 15 sec at a concentration as low as 1 nM [106], All three compounds probably elevate Cl secretion by increasing intracellular cAMP. Indeed, Klyce et al. [106] demonstrated that exposure of the mucosal side of the cornea to 1 mM dibutyryl cAMP elevated the 7SC by 144%, which correlated with a 200% change in the net CH secretion measured as 36C1 flux. This com-... 

Seifert, R., Hoer, A., Offermans, S., Buschauer, A., Schunack, W. (1992). Histamine increases cytosolic Ca2+ in dibutyryl-cAMP-differentiated HL-60 cells via H receptors and is an incomplete secretagogue. Am. Soc. Pharmacol. Exp. Therapeut. 

Darrow J, Fast VG, Kleber AG, Beyer EC, Saffitz JE Functional and structural assessment of intercellular communication. Increased conduction velocity and enhanced connexin expression in dibutyryl cAMP-treated cultured cardiac myocytes. Circ Res 1996 79 174-183. 

FIGURE 3.3 Downregulation of c-myc mRNA in HL-60 cells treated with dibutyryl cAMP (dbcAMP) and PE form DHA (Hosokawa, 2004). HL-60 cells (5x104) were incubated with (dbcAMP) after preincubation with 50 pM 1-oleoyl, 2-docosahexaenoyl-phosphatidyl-ethanolamine for 24h. Nitroblue tetrazolium (NBT) reducing activity in HL-60 cells was assayed. Data shown as mean value SD. p<0.01 versus control. p<0.01 versus RA. 

Effect of Dibutyryl cAMP versus cAMP on Intact Cells The physiological effects of epinephrine should in principle be mimicked by addition of cAMP to the target cells. In practice, addition of cAMP to intact target cells elicits only a minimal physiological response. Why When the structurally related derivative dibutyryl cAMP (shown below) is added to intact cells, the expected physiological response is readily apparent. Explain the basis for the difference in cellular response to these two substances. Dibutyryl cAMP is widely used in studies of cAMP function. 

The dopamine-stimulated formation of cAMP may initiate the dopamine-induced release of IR-PTH. A linear relationship exists between the dopamine-induced release of IR-PTH and the logarithm of the dopamine-induced accumulation of cAMP (17). Similarly, other agents increasing cAMP accumulation and IR-PTH release (e.g. beta-adrenergic agonists, secretin and phosphodiesterase inhibitors, also display such a log-linear relationship. Additional support for the possibility that intracellular cAMP might initiate PTH secretion comes from the observations that cholera toxin (JJ.), phosphodiesterase inhibitors (17) and dibutyryl cAMP (18), agents known to increase intracellular cAMP or mimic the biochemical effects of cAMP, increase the release of IR-PTH. 

The necessity of PKA activation for successful preconditioning is demonstrated by the following (i) the beta-adrenergic receptor blocker alprenolol partially abolished ischemic preconditioning (Lochner et al. 1999) (ii) landiolol, a short-acting beta-blocker, blunted the infarct size limitation induced by ischemic preconditioning (Sanada et al. 2004) (iii) PKA inhibitors such as H89 (Sanada et al. 2004 Inserte et al. 2004) and Rp-cAMPs (Sanada et al. 2004) blunted ischemic and dibutyryl-cAMP-induced preconditioning. 

Answer Unlike cAMP, dibutyryl cAMP passes readily through the plasma membrane. 

In addition to mobilizing internal Ca2+, glucagon promotes the net entry of extracellular Ca2+ into hepatocytes [144,145]. The effect is apparently due to increased influx of Ca2+ through a plasma membrane channel(s) [144,145], but there is also inhibition of the plasma membrane Ca2+ ATPase-pump [150-153], The mechanism by which glucagon stimulates Ca2+ entry is unknown, but it almost certainly involves cAMP since the effect can be mimicked by forskolin, dibutyryl cAMP and /3-adrenergic agonists [144,145]. It may involve cAMP-dependent phosphorylation of a Ca2+ channel analogous to the situation in cardiac and skeletal muscle [154-156], but this is strictly speculative. 

Intracellular cyclic adenosine monophosphate (cAMP)-stimulated add secretion in the isolated guinea-pig gastric mucosa was not inhibited by administration of an H2-receptor antagonist, as expected, although H 83/69 (timoprazole) induced a dose-dependent inhibition. This was the first experimental evidence for a site of inhibitory action beyond the panel of stimulatory cell membrane receptors. Interestingly, it was found that the initial lead compound (CMN 131), had no inhibitory effect on dibutyryl-cAMP-stimulated acid secretion, nor was it an H2-receptor antagonist [9],... 

Inhibits Glucagon-, Cortisol-, Epinephrine- Dibutyryl cAMP-induced adipocyte lipolysis]... 

Bld-HrTH administration to B. discoidalis in vivo or to isolated fat body fails to stimulate either fat body cAMP levels or adenylate cyclase activity and supports the previous findings (25). Nevertheless, for B. discoidalis, fat body phosphorylase activity is elevated and trehalose levels increase both in vivo and in vitro, and calcium is essential in vitro in addition to Bld-HrTH. No stimulation of trehalose synthesis is noted with agents that elevate adenylate cyclase, such as forskolin, or by inhibitors of phosphodiesterase such as theophylline or isobutylmethylxanthine (IBMX). Additions of cAMP, dibutyryl cAMP or 8-bromo-cAMP are not stimulatory to trehalose synthesis either in vivo or in vitro. This same result was observed for P. americana in that neither cAMP nor dbcAMP stimulated trehalose production by fat body in vitro, and xanthine inhibitors of phosphodiesterase that should cause accumulation of intracellular cAMP were inhibitory, except for isobutylmethylxanthine (IBMX) which was stimulatory for unknown reasons (26). We have not observed a stimulatory effect by IBMX with B. discoidalis fat body in vitro. 

Figure 10.8. Effect of cAMP on insulin secretion in pancreatic islet cells, a Stracture of the membrane-permeant analog dibutyryl-cAMP. The two butyryl groups and the acetyl group will be cleaved intracellularly, releasing cAMP. b Glucose-de-pendent insulin secretion in the presence or absence of dibutyryl-cAMP. cAMP amplifies glucose-dependent secretion, c Suppression of cAMP-mediated stimulation of insulin secretion by the a2-agonist clonidine. (Data from Life Sci. 32 191-95,1983.)...

Israbian VA, Weitman SA, Kamp DW. 1994. Dibutyryl cAMP attenuates asbestos-induced pulmonary epithelial cell cytotoxicity and decline in ATP levels. Am J Physiol 267(11) L518-L525. 

The PGE2-activated prostanoid receptors on DRG neurons (EPj, EP4, and some splice variants of EP3 receptors — EP3B and EP3( ) can be coupled to the stimulation of adenylate cyclase to raise cAMP levels. Experimental elevation of cAMP with the adenylate cyclase stimulator, forskolin, or application of membrane permeant cAMP analogues, dibutyryl cAMP (dbcAMP) and 8-bromo-cAMP, mimicked the effect of PGE2 treatment by shifting the activation... 

FIG. 3. (Left) 1 mM dibutyryl cAMP evokes an increase in TTX-R current evoked by depolarizations to a test potential of —15 mV. (Inset) Currents evoked at times 1,2,3 indicated on graph. (Right) Dideoxyforskolin (10 M) evokes a small reduction in TTX-R current amplitude while a subsequent challenge with forskolin (10 M) increases current amplitude. Data from England et al (1996). 

The hormonal regulation of GCS expression has special physiological relevance. Phenylephrine, glucagon or dibutyryl cAMP inhibit GCS activity, which decreases glutathione synthesis and leads to glutathione depletion in rat hepatocytes [26,27]. The loss of GCS activity induced by these stress hormones is mediated by phosphorylation of the catalytic GCS subunit due to activation of protein kinase A, protein kinase C or Ca -calmoduhn kinase [28]. Consequently, the stress response diminishes GSH synthesis, which may increase the availability of cysteine for the synthesis of stress proteins [14]. 

Kennedy TP, Michael JR, Hoidal JR et al. (1989). Dibutyryl cAMP, aminophylline, and B-adrenergic agonists protect against pulmonary edema caused by phosgene. J Appl Physiol, 67, 2542-2552. 

Certain proteins that appear to be present only in the synaptic plasmalem-ma have been shown to be phosphorylated specifically by cAMP-dependent kinase. Termed proteins la and Ib, these proteins are rapidly phosphorylated (in less than 5 sec) by electrical stimulation of presynaptic fibers and by application of the neurotransmitter believed to be released by the presynaptic neuron. Depolarizing agents, such as potassium and veratridine, when applied to the postsynaptic fibers, cause an enormous increase in the phosphorylation of proteins la and Ib. Dibutyryl cAMP and 8-bromo cAMP both mimic the actions of the neurotransmitters, as do phosphodiesterase inhibitors. The function of these proteins is at present unknown. 

Functional studies that have been carried out using the hsst5 gene promoter showed that 0.9 kb DNA upstream of the initiator codon directed the expression of a reporter gene construct following transfection in GHs pituitary cells but not in Chinese hamster ovary (CHO) cells (Greenwood et al. 1994). Expression of the reporter gene was further increased by dibutyryl-cAMP. In the absence of the cAMP response ele-... 

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