Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

---

Query: EC:2.3.1.21 (CPT)
4,580 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

1. The importance of adenosine 3':5'-cyclic monophosphate (cyclic AMP) and its protein kinase (protein kinase A, PKA) in promoting acetylcholine (ACh) release was studied at frog motor nerve endings. The effects of cyclic AMP-dependent protein phosphorylation on the action of adenosine receptor agonists were also investigated. 2. Cyclic AMP was delivered to a local region of the cytoplasm just beneath the plasma membrane of motor nerve endings using phospholipid vesicles (liposomes) as a vehicle. Cyclic AMP in liposomes produced a parallel reduction in the mean level of evoked ACh release (m) and spontaneous ACh release (miniature endplate potential frequency; m.e.p.p.f) in most experiments. These inhibitory effects of cyclic AMP on quantal ACh release resemble the action of adenosine. 3. The effects of global increases in cytoplasmic cyclic AMP concentrations using lipophilic cyclic AMP analogues were generally different from those observed with cyclic AMP. 8-(4-Chlorophenylthio) cyclic AMP (CPT cyclic AMP) produced approximately two fold increases in m and m.e.p.p.f. Dibutyryl cyclic AMP (db cyclic AMP) also increased m and m.e.p.p.f, with the effect on m being smaller and more variable. 4. All three cyclic AMP analogues reduced the effects of adenosine receptor agonists on spontaneous and evoked ACh release. 5. The roles of protein phosphorylation in mediating ACh release and the inhibitory effects of adenosine were studied with the protein kinase inhibitor H7. H7 (30-100 microM) produced no consistent effect on evoked or spontaneous ACh release. At these concentrations, however, H7 exerted an unfortunate inhibitory action on the nicotinic ACh receptor/ion channel. 6. H7 prevented the increases in spontaneous ACh release produced by CPT cyclic AMP (250 microM). Thus H7 is likely to inhibit PK A in frog motor nerve endings. 7. H7 did not alter the inhibitory effect of adenosine on evoked and spontaneous ACh release. 8. The results suggest: (i) that the adenylyl cyclase-cyclic AMP-PK A system is compartmentalized within the motor nerve terminal, (ii) that phosphorylation does not play a major role in ACh release and (iii) the cyclic AMP-PK A system modulates rather than mediates the inhibitory effects of adenosine.
...
PMID:The role of cyclic AMP and its protein kinase in mediating acetylcholine release and the action of adenosine at frog motor nerve endings. 217 31

Protein phosphorylation plays important roles in the mechanisms underlying serotonin (5-HT)-induced presynaptic facilitation of Aplysia sensory neurons. To study mechanisms involved in facilitation, we investigated the pattern of protein phosphorylation in sensory neurons as a function of different durations of 5-HT. Two minutes and 1.5 hr treatments with 5-HT altered the phosphorylation of 5 and 10 proteins, respectively. These different duration treatments with 5-HT produced unique effects on the phosphorylation of different sets of proteins. This result suggests that cells may encode and measure the duration of a stimulus by the pattern of specific proteins that are phosphorylated or dephosphorylated. In addition, because the changes in phosphorylation produced by 2 min treatments with 5-HT were not observed after 25 min treatments with 5-HT, mechanisms must exist for the transient phosphorylation of some proteins even when the 5-HT treatment persists. Anisomycin, an inhibitor of protein synthesis, blocked the effect of 1.5 hr treatments with 5-HT on the phosphorylation of six proteins but had no effect on the phosphorylation change of four other proteins. Both CPT-cAMP (an activator of protein kinase A) and PDAc (an activator of protein kinase C) mimicked the effects of 5-HT on four proteins. Interestingly, the effect of 5-HT on these four proteins did not require protein synthesis. CPT-cAMP, but not PDAc, mimicked the effect of 5-HT on one protein (L55) and, the effect of 5-HT on this protein appeared to require protein synthesis. Because both activation of PKA and protein synthesis are involved in the induction of long-term facilitation, protein L55 is a good candidate for a protein that might play a key role in long-term facilitation. Finally, the effects of 5-HT on four proteins were not mimicked by either CPT-cAMP or PDAc. This finding raises the interesting possibility that some effects of 5-HT are mediated by second-messenger systems other than PKA or PKC.
...
PMID:Dynamics of protein phosphorylation in sensory neurons of Aplysia. 782 47

In PC12 cells, cAMP stimulates the MAP kinase pathway by an unknown mechanism. Firstly, we examined the role of calcium ion mobilization and of protein kinase C in cAMP-stimulated MAP kinase activation. We show that cAMP stimulates p44mapk independently of these events. Secondly, we studied the role of B-Raf in this process. We observed that NGF, PMA and cAMP induce the phosphorylation of B-Raf as well as an upward shift in its electrophoretic mobility. We show that B-Raf is activated following NGF and PMA treatment of PC12 cells, and that it can phosphorylate and activate MEK-1. However, cAMP inhibits B-Raf autokinase activity as well as its ability to phosphorylate and activate MEK-1. This inhibition is likely to be due to a direct effect since we found that PKA phosphorylates B-Raf in vitro. Further, we show that B-Raf binds to p21ras, but more important, this binding to p21ras is virtually abolished with B-Raf from PC12 cells treated with CPT-cAMP. Hence, these data indicate that the PKA-mediated phosphorylation of B-Raf hampers its interaction with p21ras, which is responsible for the PKA-mediated decrease in B-Raf activity. Finally, our work suggests that in PC12 cells, cAMP stimulates MAP kinase through the activation of an unidentified MEK kinase and/or the inhibition of a MEK phosphatase.
...
PMID:Regulation of the MAP kinase cascade in PC12 cells: B-Raf activates MEK-1 (MAP kinase or ERK kinase) and is inhibited by cAMP. 783 30

Low concentrations of angiotensin II (Ang II) increase, whereas high concentrations inhibit the apical Na/H antiporter activity in the proximal tubule, but the respective roles of the different signaling pathways in mediating these effects remains unsettled. We studied the effects of both low and high doses of Ang II in the presence of selective signaling pathway inhibitors, on the apical Na/H antiport activity of rat proximal tubule. Experiments were carried out in intact cells of freshly prepared tubule fragments obtained from the outer third of cortex, that is, devoid of basolateral Na/H antiport activity in the absence of bicarbonate transport and H(+)-ATPase activity. In tubules acid-loaded by an NH4Cl prepulse, Na/H antiport activity was assessed by the initial rate of intracellular pH recovery (dpHi/dt), measured with BCECF. When tubules were preincubated with low dose Ang II (10(-11) M for 3 min), dpHi/dt increased by 25 +/- 8%, whereas incubation with high dose Ang II (10(-7) M for 3 min) decreased dpHi/dt by 30 +/- 4%, compared to control (P < 0.01 in both cases). Both effects were abolished in the presence of 2.10(-3) M amiloride. Low dose Ang II-induced increase in dpHi/dt was not affected by preincubation with a specific PKA inhibitor, Rp-CPT-cAMP 10(-4) M, and was completely abolished by preincubation with PKC inhibitors, staurosporine 10(-7) M, sphingosine 5.10(-6) M, or calphostin 10(-6) M. In addition, pretreatment of rats with pertussis toxin led to a partial inhibition of the effect of low dose Ang II. The high dose-Ang II-induced decrease in dpHi/dt was not affected by pretreatment with a calcium-calmodulin kinase inhibitor W-7 10(-4) M. Conversely, pretreatment with the cytochrome P-450 inhibitor econazole 10(-5) M reversed the inhibitory effect of high dose Ang II to a stimulatory effect (24 +/- 8%, P < 0.01), quantitatively similar to the effect of low dose Ang II. In addition, arachidonate was found to exert an econazole-sensitive dose-dependent inhibitory effect on dpHi/dt, and 5,6-EET 10(-6) M, a cytochrome P-450 derived-arachidonic acid metabolite, induced a 38 +/- 9% inhibition, similar to that observed with high dose Ang II alone. There was no additive effect of 5,6-EET and high dose Ang II. Finally, pretreatment with two PLA2 inhibitors (BromoPhenacylBromide, 6.10(-6) M, and oleyloxyethyl phosphorylcholine, 5.10(-6) M) reversed the inhibitory effect of high dose Ang II to a stimulatory effect (32 +/- 11% and 25 +/- 11%, respectively, P < 0.05 for both inhibitors). We conclude that, in intact rat proximal cells, low dose Ang II stimulates the apical Na/H antiport through a pertussis toxin-sensitive G protein-dependent PKC pathway, whereas high dose Ang II inhibits the Na/H antiport activity through the PLA2- and cytochrome P-450-dependent metabolites of arachidonate.
...
PMID:Signaling pathways in the biphasic effect of angiotensin II on apical Na/H antiport activity in proximal tubule. 891 15

The hypothesis that cAMP-dependent protein kinase (protein kinase A; PKA) is in an active state in small arteries possessing a myogenic tone was investigated in pressurized rat tail small arteries. At a pressure of 80 mmHg, these vessels constricted to 71.6 +/- 1.0% (n = 32) of the diameter of the fully relaxed state. The PKA inhibitors Rp-8-(4-chlorophenylthio)-adenosine 3',5'-cyclic monophosphothioate (Rp-CPT-cAMPS) and N-(2-([3-(4-bromophenyl)-2-propenyl]amino)-ethyl)-5- isoquinolinesulfonamide HCl (H-89) constricted these vessels dose dependently. For example, 300 microM Rp-CPT-cAMPS and 9 microM H-89 reduced vessel diameter by 11.0 +/- 1.2% (n = 8) and 14.3 +/- 3.6% (n = 5), respectively. The cGMP-dependent protein kinase (protein kinase G; PKG) inhibitor Rp-8-bromo-beta-phenyl-1,N(2)-etheno-guanosine 3', 5'-cyclic monophosphothioate (Rp-8-Br-PET-cGMPS) did not alter vessel diameter up to a concentration of 10 microM. Neither endothelium removal nor inhibition of neural transmission affected the action of Rp-CPT-cAMPS. The effect of 300 microM Rp-CPT-cAMPS was reduced by 82% after pretreatment of the vessel with 100 nM iberiotoxin, a blocker of calcium-activated potassium (K(Ca)) channels. However, the effect of 300 microM Rp-CPT-cAMPS was not altered after pretreatment with 1 mM 4-aminopyridine, a blocker of delayed rectifier potassium channels, or 10 microM ryanodine, a blocker of ryanodine receptor-generated calcium sparks. In inside-out patch-clamp experiments on cells isolated from rat tail small arteries, 10 U/ml of the catalytic subunit of PKA together with 100 microM MgATP increased K(Ca) channel activity 30.1 +/- 9. 8-fold (n = 9). Additionally, neither inhibition of PKA or PKG nor moderate activation of PKA or PKG altered the vessel response to a pressure step from 80 to 120 mmHg. These results suggest that in rat tail small arteries possessing a myogenic tone 1) PKA is in an active state modulating the level of the myogenic tone, and 2) K(Ca) channels mediate, at least partly, this effect of PKA.
...
PMID:cAMP-dependent protein kinase is in an active state in rat small arteries possessing a myogenic tone. 1048 37

Cystic fibrosis transmembrane regulator (CFTR) is reported to be preferentially regulated by membrane-bound protein kinase A (PKAII). We tested for close physical and functional association of PKA with CFTR in inside-out membrane patches excised from Calu-3 cells. In the presence of MgATP, 8-(4-chlorophenylthio)adenosine 3',5'-cyclic monophosphate (CPT-cAMP) increased the product of CFTR channel number and open probability (from 0.36 +/- 0.12 to 1.23 +/- 0.57, n = 20, P < 0.0025), and this stimulation was abolished by PKI. Thus Calu-3 membrane isolated from cells retains PKA holoenzyme that is functionally coupled to CFTR. PKAII is anchored at specific subcellular sites by A kinase anchoring proteins (AKAPs). Exposure of excised patches to HT-31, a peptide that disrupts the association of PKAII and AKAPs, prevented CPT-cAMP stimulation of CFTR. Therefore, PKA holoenzyme in isolated membrane patches is bound to AKAPs. In whole cell voltage-clamp studies, intracellular dialysis of Calu-3 cells with HT-31 blocked the activation of CFTR by extracellular adenosine. These results suggest that AKAPs mediate PKA compartmentalization with CFTR and are required for activation of CFTR by physiological regulators.
...
PMID:PKA holoenzyme is functionally coupled to CFTR by AKAPs. 1066 38

cAMP-dependent vasodilators are used to treat a variety of cardiovascular disorders; however, the signal transduction pathways and effector mechanisms stimulated by these agents are not fully understood. In the present study we demonstrate that cAMP-stimulating agents enhance the activity of the large-conductance, calcium-activated potassium (BK(Ca)) channel in single myocytes from coronary arteries by "cross-activation" of the cGMP-dependent protein kinase (protein kinase G, PKG). Single-channel patch-clamp data revealed that 10 micromol/L isoproterenol, forskolin, or dopamine opens BK(Ca) channels in coronary myocytes and that this effect is attenuated by inhibitors of PKG (KT5823; Rp-8-pCPT-cGMPS), but not by inhibiting the cAMP-dependent protein kinase (protein kinase A, PKA). In addition, a membrane-permeable analog, CPT-cAMP, also opened BK(Ca) channels in these myocytes, and this effect was reversed by KT5823. Direct biochemical measurement confirmed that dopamine or forskolin stimulates PKG activity in coronary arteries but does not elevate cGMP. Finally, the stimulatory effect of cAMP on BK(Ca) channels was reconstituted in a cell-free, inside-out patch by addition of purified PKG activated by either cGMP or cAMP. In contrast, channel gating was unaffected by exposure to the purified catalytic subunit of PKA. In summary, findings from on-cell and cell-free patch-clamp experiments provide direct evidence that cAMP-dependent vasodilators open BK(Ca) channels in coronary myocytes by cross-activation of PKG (but not via PKA). Biochemical assay confirmed this cross-activation mechanism of cAMP action in these arteries. This signaling pathway is a novel mechanism for regulation of potassium channel activity in vascular smooth muscle and other cells.
...
PMID:cAMP-dependent vasodilators cross-activate the cGMP-dependent protein kinase to stimulate BK(Ca) channel activity in coronary artery smooth muscle cells. 1078 13

The mechanism(s) by which dopamine inhibits Na+-K+-ATPase activity in the renal proximal tubule is still controversial. We studied the short-term effects of dopamine on the sodium pump in rat renal proximal tubule suspensions with the 86Rb uptake method. Dopamine and the D1-like agonist, SKF81297, initially stimulated Na+-K+-ATPase activity at 5 min and subsequently inhibited it at 10 min and 20 min; the inhibition by 10 microM dopamine at 20 min was 21.3 +/- 4.5%. The inhibitory effect of dopamine on Na+-K+-ATPase activity was mimicked by thymeleatoxin (a classical protein kinase C [PKC] agonist) while Sp-8-CPT-cAMPS (a protein kinase A [PKA] agonist) had no effect. However, the combination of the PKC and PKA agonists mimicked the biphasic effects of dopamine and SKF81297. Rp-8-CPT-cAMPS (a PKA inhibitor), U-73122 (a phospholipase C inhibitor), or calphostin C (a PKC inhibitor), blocked the dopamine-mediated biphasic effects on Na+-K+-ATPase activity. It is suggested that the biphasic effects of dopamine on Na+-K+-ATPase activity (an initial stimulation and a subsequent inhibition) are transduced by activating both PKA and PKC through a D1-like receptor.
...
PMID:Biphasic effects of dopamine on 86rubidium uptake in rat renal proximal tubules. 1080 34

Cystic fibrosis is caused by the aberrant function of the cystic fibrosis transmembrane conductance regulator (CFTR) protein. We examined whether intramolecular binding interactions involving the regulatory (R) domain contributed to CFTR regulation and function. When the R-domain (amino acids 596-836) was coexpressed with Delta1-836 CFTR (a carboxyl hemi-CFTR beginning immediately after the R-domain), strong binding between the two polypeptides was exhibited. The R-domain that co-immunoprecipitated with Delta1-836 exhibited a slower mobility on SDS-PAGE that resulted from phosphorylation of the protein. A larger CFTR polypeptide that included the R-domain (M837X) also exhibited a phosphorylation-dependent mobility shift when coexpressed with Delta1-836. Moreover, coexpression of M837X and Delta1-836 led to enhanced halide permeability in living cells. The activity, unlike in full-length CFTR, was present without forskolin activation, but still sensitive to the PKA inhibitor, Rp-8-CPT-cAMPS. This PKA inhibition of activity was found to be dependent on the carboxy region of the R-domain, amino acids 723-836. Our results indicate that the R-domain binds CFTR residues after amino acid 836 and that this binding facilitates phosphorylation and CFTR activation. We have also characterized a subdomain within CFTR (residues 723-837) that is necessary for PKA-dependent constitutive activation. Finally, these experiments demonstrate that constitutive CFTR activity can be accomplished by at least two mechanisms: (1) direct modulation of the R-domain to abrogate PKA regulation and (2) modifications that increase R-domain susceptibility to steady-state phosphorylation through PKA.
...
PMID:R-domain interactions with distal regions of CFTR lead to phosphorylation and activation. 1093 5

Pigmented (PE) and nonpigmented (NPE) ciliary epithelial cells comprise the ciliary epithelium, the site of aqueous humor formation in the eye. In man, catecholamines increase the rate of aqueous humor formation, but the mechanism underlying these effects is not understood. Recent evidence suggests that Na-K-Cl cotransport plays a central role in blood-to-aqueous chloride transport across ciliary epithelium in cow and rabbit. We therefore investigated whether catecholamines stimulate Na-K-Cl cotransport in human PE cells. Na-K-Cl cotransporter protein was detected as a 170 kDa protein band on immunoblots. Immunofluorescence microscopy detected cotransporter on the basolateral membranes of the PE layer of ciliary epithelium from a human donor. Cotransporter immunofluorescence was also detected in cultured PE cells. Na-K-Cl cotransport activity measured as ouabain-insensitive bumetanide-sensitive(86)Rb uptake was stimulated by isoproterenol 1.6-fold, with an EC(50) = 28 n M and maximal stimulation at 1 microM. Other transport mechanisms involved in(86)Rb uptake were not affected. Stimulation by 1 microM isoproterenol was blocked by 10 n M ICI 118,551, a beta(2)-specific receptor antagonist, whereas the receptor subtype-specific antagonists yohimbine (alpha(2)), prazosin (alpha(1)) and atenolol (beta(1)) were ineffective. Norepinephrine stimulation (EC(50) = 280 n M) was also blocked by ICI 118,551. Dopamine stimulated Na-K-Cl cotransport 1.6-fold with an EC(50) = 14 microM. The dopamine effect could not be blocked by 10 microM SCH 23390, a D1-antagonist, but was abolished by ICI 118,551. Forskolin and CPT-cAMP stimulated Na-K-Cl cotransport 1.79- and 1.71-fold, respectively, whereas the inactive forskolin analogue 1,9-dideoxyforskolin had no effect. However, high concentrations of the PKA inhibitors PKI amide 14-22 and KT 5720 were needed to inhibit both PKA activity in cell lysates and isoproterenol stimulation of cotransport. This finding may indicate the presence of a novel PKA isoform in PE cells. Inhibitors of other protein kinases, including myosin light chain kinase, protein kinase G, calmodulin-dependent kinase and tyrosine kinase, were without effect on stimulated Na-K-Cl cotransport. When EC(50)s for catecholaminergic stimulations of Na-K-Cl cotransport in PE were compared to those in NPE, values within five-fold of one another were seen for isoproterenol and norepinephrine. In contrast, dopamine was 28-fold more potent in NPE than in PE. The data suggest that both PE and NPE possess beta(2)adrenergic receptors, but only NPE cells possess dopamine D1 receptors linked to Na-K-Cl cotransport.
...
PMID:Catecholaminergic regulation of Na-K-Cl cotransport in pigmented ciliary epithelium: differences between PE and NPE. 1113 77


1 2 3 4 5 6 7 Next >>

---