Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “CAMPS”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,189 records · Page 66Linked to original sources
PubMed1996

Cholera and pertussis toxins reveal multiple regulation of cAMP levels in the rabbit carotid body.

It is known that hypoxia (PO2 approximately equal to 66-18 mm Hg), acting via unknown receptors, increases carotid body cAMP levels in Ca(2+)-free solutions, indicating that low PO2 activates adenylate cyclases independently of the action of the released neurotransmitters. The aim of the present work was to investigate the involvement of G proteins in the genesis of the basal level of cAMP and on the increase in cAMP induced by low PO2. In carotid body homogenates, cholera toxin- and pertussis toxin-induced [32P]ADP-ribosylation of two protein bands of approximately equal to 42 and 45 kDa, and approximately equal to 39 and 40 kDa respectively; in both cases, prior incubation of the carotid bodies with the toxins reduced [32P]ADP-ribosylation by > 90%. In intact carotid bodies, cholera toxin treatment increased cAMP levels more in normoxic than in hypoxic organs, indicating that hypoxia releases neurotransmitters acting on receptors negatively coupled to adenylate cyclases. Cholera toxin-treated carotid bodies incubated in Ca(2+)-free solution had identical cAMP levels in normoxia and in hypoxia. In pertussis toxin-treated normoxic carotid bodies the cAMP level was close to control, but in pertussis toxin-treated hypoxic carotid bodies cAMP rose to a level similar to those seen in normoxic cholera toxin-treated organs, indicating that low PO2 releases neurotransmitters acting on receptors positively coupled to adenylate cyclases. Pertussis toxin-treated carotid bodies incubated in Ca(2+)-free solution lost their capacity to increase cAMP in response to hypoxia, indicating that a G protein sensitive to pertussis toxin is needed for this response. This implies that the carotid bodies express a pertussis toxin-sensitive G protein positively coupled to adenylate cyclases, or that a Gs protein requiring the cooperative action of Go/Gi donated beta gamma subunits mediates the increase in cAMP level produced by hypoxia.

Adenosine Diphosphate Ribose↗
PubMed2001

cAMP-regulated guanine nucleotide exchange factor II (Epac2) mediates Ca2+-induced Ca2+ release in INS-1 pancreatic beta-cells.

1. The signal transduction pathway responsible for cAMP-dependent Ca2+-induced Ca2+ release (CICR) from endoplasmic reticulum Ca2+ stores was assessed in the insulin-secreting cell line INS-1. 2. CICR was triggered by the GLP-1 receptor agonist exendin-4, an effect mimicked by caffeine, Sp-cAMPS or forskolin. CICR required influx of Ca2+ through L-type voltage-dependent Ca2+ channels, and was blocked by treatment with nimodipine, thapsigargin, or ryanodine, but not by the IP3 receptor antagonist xestospongin C. 3. Treatment with the cAMP antagonist 8-Br-Rp-cAMPS blocked CICR in response to exendin-4, whereas the PKA inhibitor H-89 was ineffective when tested at a concentration demonstrated to inhibit PKA-dependent gene expression. 4. RT-PCR of INS-1 cells demonstrated expression of mRNA coding for the type-II isoform of cAMP-regulated guanine nucleotide exchange factor (cAMP-GEF-II, Epac2). 5. CICR in response to forskolin was blocked by transient transfection and expression of a dominant negative mutant isoform of cAMP-GEF-II in which inactivating mutations were introduced into the exchange factor's two cAMP-binding domains. 6. It is concluded that CICR in INS-1 cells results from GLP-1 receptor-mediated sensitization of the intracellular Ca2+ release mechanism, a signal transduction pathway independent of PKA, but which requires cAMP-GEF-II.

Animals↗
PubMed2005

cAMP inhibits CSF-1-stimulated tyrosine phosphorylation but augments CSF-1R-mediated macrophage differentiation and ERK activation.

Macrophage colony stimulating factor (M-CSF) or CSF-1 controls the development of the macrophage lineage through its receptor tyrosine kinase, c-Fms. cAMP has been shown to influence proliferation and differentiation in many cell types, including macrophages. In addition, modulation of cellular ERK activity often occurs when cAMP levels are raised. We have shown previously that agents that increase cellular cAMP inhibited CSF-1-dependent proliferation in murine bone marrow-derived macrophages (BMM) which was associated with an enhanced extracellular signal-regulated kinase (ERK) activity. We report here that increasing cAMP levels, by addition of either 8-bromo cAMP (8BrcAMP) or prostaglandin E(1) (PGE1), can induce macrophage differentiation in M1 myeloid cells engineered to express the CSF-1 receptor (M1/WT cells) and can potentiate CSF-1-induced differentiation in the same cells. The enhanced CSF-1-dependent differentiation induced by raising cAMP levels correlated with enhanced ERK activity. Thus, elevated cAMP can promote either CSF-1-induced differentiation or inhibit CSF-1-induced proliferation depending on the cellular context. The mitogen-activated protein kinase/extracellular signal-related protein kinase kinase (MEK) inhibitor, PD98059, inhibited both the cAMP- and the CSF-1R-dependent macrophage differentiation of M1/WT cells suggesting that ERK activity might be important for differentiation in the M1/WT cells. Surprisingly, addition of 8BrcAMP or PGE1 to either CSF-1-treated M1/WT or BMM cells suppressed the CSF-1R-dependent tyrosine phosphorylation of cellular substrates, including that of the CSF-1R itself. It appears that there are at least two CSF-1-dependent pathway(s), one MEK/ERK dependent pathway and another controlling the bulk of the tyrosine phosphorylation, and that cAMP can modulate signalling through both of these pathways.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1990

Effects of isozyme-selective phosphodiesterase inhibitors on rat aorta and human platelets: smooth muscle tone, platelet aggregation and cAMP levels.

The inhibitors of the cGMP-inhibited, low-Km cAMP phosphodiesterase--milrinone and OPC 3911--and an inhibitor of a non-cGMP-inhibited low-Km cAMP phosphodiesterase--rolipram--were used to evaluate the functional importance of the two cAMP phosphodiesterase activities in vascular smooth muscle and in platelets. Vinpocetine, an inhibitor of a calcium-calmodulin-dependent phosphodiesterase was also studied. OPC 3911 and milrinone relaxed the contracted rat aorta, inhibited ADP-induced platelet aggregation and also enhanced isoprenaline-induced relaxation as well as the antiaggregatory effects of adenosine. In platelets, OPC 3911 and milrinone increased cAMP levels, but in the rat aorta the increase was significant only for milrinone (OPC 3911 P = 0.062). In both tissues OPC 3911 and milrinone enhanced the increase in cAMP caused by activators of adenylate cyclase (isoprenaline/adenosine). Rolipram had no effects on aggregation or cAMP levels in platelets and no overadditive effects in combination with adenosine. Rolipram had little effect on relaxation and cAMP levels, did not alter isoprenaline-induced relaxation of guanfacin-contracted rat aorta, but showed synergistic effects with isoprenaline in raising cAMP levels. In PGF2 alpha-contracted aorta rolipram enhanced relaxation caused by isoprenaline. Vinpocetine had a relaxant effect without affecting cAMP levels, but had no effect on platelets. These results support the concept that the cGMP-inhibited phosphodiesterase is an important modulator of vascular smooth muscle tone and platelet function. The role of the non-cGMP-inhibited phosphodiesterase in these tissues is less obvious.

Animals↗
PubMed2002

Regulation of Cl--HCO3- exchangers by cAMP-dependent protein kinase in adult rat hippocampal CA1 neurons.

The contributions of HCO(3)(-)-dependent, DIDS-sensitive mechanisms to the maintenance of steady-state pH(i), and the regulation of their activities by cAMP-dependent protein kinase (PKA), were investigated in CA1 neurons with the H(+)-sensitive fluorophore, BCECF. The addition of HCO(3)(-)/CO(2) to neurons with "low" (pH(i) < or = 7.20) and "high" (pH(i) > 7.20) initial pH(i) values under Hepes-buffered conditions, increased and decreased steady-state pH(i), respectively. Conversely, under HCO(3)(-)/CO(2)-buffered conditions, DIDS caused pH(i) to decrease and increase in neurons with low and high initial pH(i) values, respectively. In the presence, but not the absence, of HCO(3)(-), the PKA inhibitor Rp-adenosine-3',5'-cyclic monophosphorothioate (Rp-cAMPS; 50 microM) evoked DIDS-sensitive increases and decreases in pH(i) in neurons with low and high initial pH(i) values, respectively. In contrast, in neurons with low initial pH(i) values, activation of PKA with the Sp isomer of cAMPS (Sp-cAMPS; 25 microM) elicited increases in pH(i) that were smaller in the presence than in the absence of HCO(3)(-), whereas in neurons with high initial pH(i) values, Sp-cAMPS-evoked rises in pH(i) were larger in the presence than in the absence of HCO(3)(-); the differences between the effects of Sp-cAMPS on pH(i) under the different buffering conditions were attenuated by DIDS. Consistent with the possibility that changes in the activities of HCO(3)(-)-dependent, DIDS-sensitive mechanisms contribute to the steady-state pH(i) changes evoked by the PKA modulators, in neurons with initial pH(i) values < or = 7.20, Rp-cAMPS concurrently inhibited Na(+)-independent Cl(-)-HCO(3)(-) exchange and stimulated Na(+)-dependent Cl(-)-HCO(3)(-) exchange; in contrast, Sp-cAMPS concurrently stimulated Na(+)-independent Cl(-)-HCO(3)(-) exchange and inhibited Na(+)-dependent Cl(-)-HCO(3)(-) exchange. Data from a limited number of neurons with initial pH(i) values > 7.20 suggested that the directions of the reciprocal changes in anion exchange activities (inhibition or stimulation) evoked by Rp- and Sp-cAMPS may be opposite in cells with low vs. high resting pH(i) values. Taken together, the results indicate that the effects of modulating PKA activity on steady-state pH(i) in rat CA1 neurons under HCO(3)(-)/CO(2)-buffered conditions reflect not only changes in Na(+)-H(+) exchange activity but also changes in Na(+)-dependent and Na(+)-independent Cl(-)-HCO(3)(-) exchange activity that, in turn, may be dependent upon the initial pH(i).

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed2004

Adenovirus-mediated delivery and expression of a cAMP-dependent protein kinase inhibitor gene to BEAS-2B epithelial cells abolishes the anti-inflammatory effects of rolipram, salbutamol, and prostaglandin E2: a comparison with H-89.

cAMP-elevating drugs are thought to mediate their biological effects by activating the cAMP/cAMP-dependent protein kinase (PKA) cascade. However, this hypothesis is difficult to confirm due to a lack of selective inhibitors. Here, we have probed the role of PKA in mediating inhibitory effects of several cAMP-elevating drugs in BEAS-2B epithelial cells using an adenovirus vector encoding a PKA inhibitor protein (PKIalpha) and have compared it to H-89, a commonly used small molecule PKA inhibitor. Initial studies established efficient gene transfer and confirmed functionality of PKIalpha 48 h after virus infection. All cAMP-elevating drugs tested promoted the phosphorylation of cAMP response element-binding protein (CREB), activated a cAMP response element (CRE)-driven luciferase reporter gene, and suppressed both granulocyte/macrophage colony-stimulating factor (GM-CSF) generation and [(3)H]arachidonic acid (AA) release in response to interleukin-1beta and monocyte chemotactic protein (MCP)-1, respectively. These effects were abolished by PKIalpha. In contrast, H-89 behaved unpredictably under the same conditions. Thus, although CREB phosphorylation evoked by a range of cAMP-elevating drugs was abolished by H-89, neither activation of the CRE-dependent luciferase reporter gene construct nor the inhibition of GM-CSF generation was inhibited. Paradoxically, H-89 antagonized MCP-1-induced [(3)H]AA release and enhanced the inhibitory effect of submaximal concentrations of rolipram and 8-bromo-cAMP. We suggest that expression of PKIalpha in susceptible cells provides a simple and unambiguous way to assess the role of PKA in cAMP signaling and to probe the mechanism of action of other drugs and cAMP-dependent responses where the participation of PKA is equivocal. Furthermore, these data suggest that H-89 is not a selective inhibitor of PKA and should be avoided.

Activating Transcription Factor 1↗
PubMed2005

Intracellular cAMP and calcium signaling by serotonin in mouse cumulus-oocyte complexes.

cAMP and intracellular Ca2+ are important second messengers involved in mammalian follicular growth and oocyte meiotic maturation. We investigated the capacity of the neurohormone serotonin (5-hydroxytryptamine, 5-HT) to regulate intracellular cAMP and Ca2+ in mouse oocytes and surrounding cumulus cells. On the basis of a reverse transcription-polymerase chain reaction study, 5-HT7 receptor mRNA is expressed in cumulus cells, oocytes, and embryos up to the four-cell stage, and 5-HT2A and 5-HT2B receptor mRNAs are expressed in cumulus cells only, whereas 5-HT2C, 5-HT4, and 5-HT6 receptors are expressed in neither oocytes nor cumulus cells. The addition of 5-HT (10 nM to 10 microM) to isolated metaphase II oocytes had no effect on their internal cAMP or Ca2+ levels, whereas it caused dose-dependent cAMP and Ca2+ increases in cumulus cells. This cAMP increase in cumulus cells could be mimicked by 5-HT agonists with the following order of potency: 5-HT > 8-hydroxy-2-(di-n-propylamino) tetralin = alpha-methyl-5-HT = 5-carboxamidotryptamine maleate > 2-[1-(4-piperonyl)piperazinyl]benzo-triazole, thereby supporting a preferential involvement of 5-HT7 receptors. As measured with cumulus cells preloaded with fura-2/acetoxymethyl ester (AM), the addition of 5-HT also caused dose-dependent Ca2+ increases, which were probably linked to detected 5-HT2A and 5-HT2B receptors. Adding the Ca2+ ionophore ionomycin to cumulus cells resulted in both Ca2+ and cAMP elevations, whereas preincubation of cells with the Ca2+ chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA)-AM abolished the 5-HT-induced Ca2+ increase and reduced the cAMP increase, indicating cross-talk between the 5-HT-sensitive Ca2+ and cAMP pathways. Our results show that 5-HT may be a local regulator in mouse cumulus-oocyte complexes through its actions on cAMP and Ca2+ signaling, as mediated by 5-HT2A, 5-HT2B, and 5-HT7 receptors.

Animals↗
PubMed1989

Cloning and expression of a cohemolysin, the CAMP factor of Actinobacillus pleuropneumoniae.

The genetic determinant of the cohemolysin which is responsible for the CAMP phenomenon, a cohemolysis, of Actinobacillus pleuropneumoniae was cloned in Escherichia coli. Total DNA from the A. pleuropneumoniae serotype 1 type strain 4074 was used to construct a gene library in plasmid pUC18 in E. coli JM83. A total of 10,500 clones containing recombinant plasmids have been screened for hemolysis on blood plates. Fifty-five clones which showed a weak hemolytic response after 24 to 48 h of incubation were screened for the CAMP reaction with Staphylococcus aureus. This led to the identification of one clone which showed a positive CAMP reaction. Immunoblot analysis revealed that the recombinant strain expressed a protein with a molecular mass of 27,000 daltons, similar in size to the CAMP protein of the group B streptococci. Rabbit antibodies against the CAMP+ clone neutralized the CAMP reaction mediated by the E. coli strain containing the cloned CAMP gene as well as that of A. pleuropneumoniae. Antibodies raised against the cloned CAMP cohemolysin cross-reacted with Streptococcus agalactiae protein B. We designate the 27,000-dalton molecule CAMP factor protein and name its corresponding gene cfp.

Actinobacillus↗
PubMed1991

Antagonists of epithelial chloride channels inhibit cAMP synthesis.

In past studies we observed that the chloride channel blocker, diphenylamine-2-carboxylate (DPC) and chemically related drugs (Hoechst compounds 131, 143, 144) inhibited cAMP formation in mouse pituitary tumor cells. The object of this study was to determine whether these drugs inhibited chloride transport in human T-84 colonic carcinoma cells through an effect on cAMP metabolism. Chloride secretion (measured as 125I efflux from isotope-preloaded cells) was stimulated in a concentration-dependent manner by vasoactive intestinal polypeptide (VIP) (EC50 = 1.5 x 10(-10) M) which similarly increased cAMP synthesis (EC50 = 1.6 x 10(-8) M). The cAMP response to VIP was inhibited 17, 52, 55, and 78% maximally by DPC and compounds 144, 143, and 131, respectively. In untreated T-84 cells, 125I secretion fell by 66% after 3 min; VIP (10(-7) M) increased secretion about fivefold over the same period. Both basal and VIP-stimulated 125I secretion were inhibited up to 60% by compound 131. Pretreatment of cells with pertussis toxin did not attenuate the inhibitory effect of channel blockers on either VIP-stimulated cAMP synthesis or 125I secretion. The cationophore, A-23187, which had no effect on cAMP formation, and 8-Br-cAMP both stimulated 125I secretion from T-84 cells. These secretory responses were inhibited by compound 131. The mechanism by which phenylanthranilic acids antagonize cAMP synthesis and its significance is not known; however, the data suggest that this family of drugs may inhibit chloride transport by both cAMP-dependent and independent mechanisms.

Chloride Channels↗
PubMed2005

Beta-adrenergic- and muscarinic receptor-induced changes in cAMP activity in adult cardiac myocytes detected with FRET-based biosensor.

beta-Adrenergic receptor activation regulates cardiac myocyte function through the stimulation of cAMP production and subsequent activation of protein kinase A (PKA). Furthermore, muscarinic receptor activation inhibits as well as facilitates these cAMP-dependent effects. However, it has not always been possible to correlate the muscarinic responses with the direct measurement of changes in cellular cAMP activity. Genetically encoded biosensors have recently been developed, making it possible to monitor real-time changes in cAMP and PKA activity at the single cell level. One such biosensor consists of the regulatory and catalytic subunits of PKA labeled with cyan and yellow fluorescent proteins, respectively. Changes in cAMP activity affecting the association of these labeled PKA subunits can be detected as changes in fluorescence resonance energy transfer. In the present study, an adenovirus-based approach was developed to express this recombinant protein complex in adult cardiac myocytes and use it to monitor changes in cAMP activity produced by beta-adrenergic and muscarinic receptor activation. The biosensor expressed with the use of this system is able to detect changes in cAMP activity produced by physiologically relevant levels of beta-adrenergic receptor activation without disrupting normal functional responses. It was also possible to directly demonstrate the complex temporal pattern of inhibitory and stimulatory changes in cAMP activity produced by muscarinic receptor activation in these cells. The adenovirus-based approach we have developed should facilitate the use of this biosensor in studying cAMP and PKA-dependent signaling mechanisms in a wide variety of cell types.

Adenoviridae↗
PubMed1982

Effect of cholera toxin on cAMP levels and Na+ influx in isolated intestinal epithelial cells.

Freshly isolated chicken intestinal cells contain approximately 20 pmol adenosine 3',5'-cyclic monophosphate (cAMP)/mg cellular protein. Incubation with 3 micrograms/ml cholera toxin (CT) at 37 degrees C induces an elevation of cellular cAMP beginning 10-15 min after initial exposure. The response is linear with time for 40-50 min and causes a six- to eightfold increase over control levels at steady state. Dibutyryl cAMP and agents that increase cAMP production inhibit Na+ influx into the isolated enterocytes. Chlorpromazine completely abolishes the toxin-induced elevation of cAMP in the isolated cells and also reverses the effect on Na+ entry. The data provide evidence for a cAMP-mediated control of intestinal cell Na+ uptake, which may represent the mechanistic basis for the antiabsorptive effect of CT on Na+ during induction of intestinal secretory activity. Studies on the time-dependent effects of chlorpromazine on both intracellular cAMP concentration and Na+ influx suggest that the reactivation of the Na+ transport system after cAMP-induced inhibition is slow relative to the disappearance of cAMP.

Animals↗
PubMed1990

Effect of oxygen tension on catecholamine-induced formation of cAMP and on swelling of carp red blood cells.

We studied the effects of beta-adrenergic stimulation on the formation of adenosine 3',5'-cyclic monophosphate (cAMP) and on the cell volume in carp red blood cells in normoxia (PO2 = 150 mmHg) and hypoxia (PO2 = 8 mmHg). Accumulation of cAMP was the prerequisite for adrenergic cell swelling. Cell swelling was induced by beta-agonists, forskolin, and 8-bromo-cAMP. The amount of cAMP required for adrenergic swelling was minimal; swelling was observed at cAMP concentrations greater than 100 nM. Maximal increase in cell volume was observed at 200 nM cAMP. These values were independent of both the oxygen tension and the beta-agonist used. Norepinephrine caused the largest accumulation of cAMP, followed by isoproterenol and epinephrine. At hypoxic conditions, the cAMP concentrations obtained after stimulation with the natural catecholamines norepinephrine and epinephrine were greater than at normoxic conditions. The catecholamines caused appreciable cell swelling at lower concentrations in hypoxia than in normoxia. Thus the number of beta-adrenergic receptors, and their inherent ligand affinities, may be higher in hypoxic than in normoxic carp red blood cells. Oxygen tension had a pronounced effect on the magnitude of the adrenergic swelling. The maximal increase in cell volume was 5-7% in hypoxia, whereas in normoxia it was only approximately 2%. This was not due to differences in cAMP formation, but possibly to a greater activity of the Na(+)-H+ exchanger in hypoxic than in normoxic conditions.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1994

cAMP and inositol 1,4,5-trisphosphate increase Ca2+ in HT-29 cells by activating different Ca2+ influx pathways.

Ca2+ plays a central role in regulating transepithelial fluid and electrolyte transport in intestinal epithelial cells. To investigate the mechanisms regulating the cytosolic free Ca2+ concentration ([Ca2+]c), we examined the effect of secretory agonists on [Ca2+]c in the intestinal epithelial cell line HT-29 clone 19A cells. We found that [Ca2+]c increased after addition of either adenosine 3',5'-cyclic monophosphate (cAMP)-dependent agonists or a D-myo-inositol 1,4,5-trisphosphate [Ins(1,4,5)P3]dependent agonist carbachol. Several lines of evidence suggest that cAMP- and Ins(1,4,5)P3-dependent agonists act through separate pathways. First, isoproterenol and forskolin increased cellular levels of cAMP but not Ins(1,4,5)P3, whereas carbachol increased cellular levels of Ins(1,4,5)P3 and stimulated inositol phosphate turnover without increasing cAMP. Second, carbachol increased [Ca2+]c by stimulating the release of Ca2+ from intracellular stores and influx of extracellular Ca2+. In contrast, cAMP agonists increased [Ca2+]c by stimulating Ca2+ influx alone. Third, the responses to maximal concentrations of cAMP agonists and carbachol were approximately additive. Finally, Ins(1,4,5)P3- but not cAMP agonist-dependent Ca2+ influx was inhibited by inorganic Ca2+ channel blockers. Thus, in intestinal epithelial cells, [Ca2+]c is regulated by at least two different second-messenger pathways, involving Ins(1,4,5)P3 or cAMP. In addition, cAMP stimulates influx of extracellular Ca2+ through a pathway distinct from that mediated by Ins(1,4,5)P3.

1-Methyl-3-isobutylxanthine↗
PubMed1995

cAMP evokes a rise in intracellular Na+ mediated by Na+ pump inhibition in rat aortic smooth muscle cells.

The effect of adenosine 3',5'-cyclic monophosphate (cAMP) on intracellular Na+ concentration ([Na+]i) was studied in primary cultured vascular smooth muscle cells from rat aorta. [Na+]i was measured using digital imaging of cells loaded with the Na(+-)sensitive fluorescent dye sodium-bonding benzofuran isophthalate. The cAMP level was raised by 1) the membrane-permeable cAMP derivative 8-bromoadenosine 3',5'-cyclic monophosphate, 2) the combination of the adenylate cyclase activator forskolin and the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine, and 3) the beta-adrenoceptor agonist isoproterenol. All three methods caused a dose-dependent continuous rise in [Na+]i during 40-60 min of observations. A rise in [Na+]i may be caused by stimulation of the Na+ influx and/or inhibition of Na+ efflux; therefore, the involvement of both mechanisms was studied. Elevation of the cAMP level had no effect on Na+ influx, measured as the rate of rise of [Na+]i when Na+ efflux was inhibited with 1 mM ouabain. In contrast, elevation of the cAMP level attenuated Na+ efflux, measured as the rate of decline of [Na+]i in Na(+)-loaded cells exposed to Na(+)-free medium. cAMP-induced inhibition of Na+ efflux was not observed when the Na+ pump was inhibited; therefore, cAMP inhibits the Na+ pump-mediated component of Na+ efflux. Agents that raise the cAMP level also inhibited, in a dose-dependent fashion, ouabain-sensitive 86Rb uptake in rat aortic rings. The latter observation confirms that the cAMP-induced inhibition of the Na+ pump occurs both in cultured cells and in the native tissue.(ABSTRACT TRUNCATED AT 250 WORDS)

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1998

Blockade by cAMP of native sodium channels of adult rat skeletal muscle fibers.

Although the skeletal muscle sodium channel is a good substrate for cAMP-dependent protein kinase (PKA), no functional consequence was observed for this channel expressed in heterologous systems. Therefore, we investigated the effect of 8-(4-chlorophenylthio)adenosine 3',5'-cyclic monophosphate (CPT-cAMP), a membrane-permeable cAMP analog, on the native sodium channels of freshly dissociated rat skeletal muscle fibers by means of the cell-attached patch-clamp technique. Externally applied CPT-cAMP (0.5 mM) reduced peak ensemble average currents by approximately 75% with no change in kinetics. Single-channel conductance and normalized activation curves were unchanged by CPT-cAMP. In contrast, steady-state inactivation curves showed a reduction of the maximal available current and a negative shift of the half-inactivation potential. Similar effects were observed with dibutyryl adenosine 3',5'-cyclic monophosphate but not with cAMP, which does not easily permeate the cell membrane. Incubation of fibers for 1 h with 10 microM H-89, a PKA inhibitor, did not prevent the effect of CPT-cAMP. Finally, the beta-adrenoreceptor agonist isoproterenol mimicked CPT-cAMP when applied at 0.5 mM but had no effect at 0.1 mM. These results indicate that cAMP inhibits native skeletal muscle sodium channels by acting within the fiber, independently of PKA activation.

Adrenergic beta-Agonists↗
PubMed2000

cAMP-activated anion conductance is associated with expression of CFTR in neonatal mouse cardiac myocytes.

In this study, patch-clamp techniques were applied to cultured neonatal mouse cardiac myocytes (NMCM) to assess the contribution of cAMP stimulation to the anion permeability in this cell model. Addition of either isoproterenol or a cocktail to raise intracellular cAMP increased the whole cell currents of NMCM. The cAMP-dependent conductance was largely anionic, as determined under asymmetrical (low intracellular) Cl(-) conditions and symmetrical Cl(-) in the presence of various counterions, including Na(+), Mg(2+), Cs(+), and N-methyl-D-glucamine. Furthermore, the cAMP-stimulated conductance was also permeable to ATP. The cAMP-activated currents were inhibited by diphenylamine-2-carboxylate, glibenclamide, and an anti-cystic fibrosis transmembrane conductance regulator (CFTR) monoclonal antibody. The anti-CFTR monoclonal antibody failed, however, to inhibit an osmotically activated anion conductance, indicating that CFTR is not linked to osmotically stimulated currents in this cell model. Immunodetection studies of both neonatal mouse heart tissue and cultured NMCM revealed that CFTR is expressed in these preparations. The implication of CFTR in the cAMP-stimulated Cl(-)- and ATP-permeable conductance was further verified with NMCM of CFTR knockout mice [cftr(-/-)] in which cAMP stimulation was without effect on the whole cell currents. In addition, stimulation with protein kinase A and ATP induced Cl(-)-permeable single-channel activity in excised, inside-out patches from control, but not cftr(-/-) NMCM. The data in this report indicate that cAMP stimulation of NMCM activates an anion-permeable conductance with functional properties similar to those expected for CFTR, thus suggesting that CFTR may be responsible for the cAMP-activated conductance. CFTR may thus contribute to the permeation and/or regulation of Cl(-)- and ATP-permeable pathways in the developing heart.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed2001

Participation of cAMP in a signal-transduction pathway relating erythrocyte deformation to ATP release.

Previously, we reported that red blood cells (RBCs) of rabbits and humans release ATP in response to mechanical deformation and that this release of ATP requires the activity of the cystic fibrosis transmembrane conductance regulator (CFTR). It was reported that cAMP, acting through a cAMP-dependent protein kinase, PKA, is an activator of CFTR. Here we investigate the hypothesis that cAMP stimulates ATP release from RBCs. Incubation of human and rabbit RBCs with the direct activator of adenylyl cyclase, forskolin (10 or 100 microM), with IBMX (100 microM), resulted in ATP release and increases in intracellular cAMP. In addition, epinephrine (1 microM), a receptor-mediated activator of adenylyl cyclase, stimulated ATP release from rabbit RBCs. Moreover, incubation of human and rabbit RBCs with an active cAMP analog [adenosine 3'5'-cyclic monophosphorothioate Sp-isomer (Sp-cAMP, 100 microM)] resulted in ATP release. In contrast, forskolin and Sp-cAMP were without effect on dog RBCs, cells known not to release ATP in response to deformation. When rabbit RBCs were incubated with the inactive cAMP analog and inhibitor of PKA activity, adenosine 3',5'-cyclic monophosphorothioate Rp-isomer (100 microM), deformation-induced ATP release was attenuated. These results are consistent with the hypothesis that adenylyl cyclase and cAMP are components of a signal-transduction pathway relating RBC deformation to ATP release from human and rabbit RBCs.

1-Methyl-3-isobutylxanthine↗
PubMed1985

Calcium, a "third messenger" of cAMP-stimulated adrenal steroid secretion.

This study examines the role of extracellular calcium and calcium mobilization from intracellular stores in mediating cAMP-stimulated steroid secretion by rat adrenal glomerulosa cells (GC) and fasciculata cells (FC). When GC were incubated acutely in a calcium-deficient buffer, cAMP failed to significantly increase aldosterone secretion above base line. Aldosterone secretion, however, rose from 17 +/- 2 to 32 +/- 4 ng/10(6) cells (P less than 0.01) as calcium in the medium was increased from 0 to 3.5 mM. In contrast, cAMP-stimulated corticosterone production by FC was not influenced by changes in the external calcium concentration. Lanthanum (10(-4) M), an inhibitor of calcium influx, reduced cAMP-stimulated aldosterone secretion from 69 +/- 10 to 42 +/- 5 ng/10(6) cells (P less than 0.01) but failed to alter cAMP-stimulated fasciculata steroidogenesis. Depletion of intracellular calcium stores, achieved by incubating with EGTA, markedly blunted cAMP-stimulated corticosterone secretion in GC from 666 +/- 126 to 32 +/- 6 ng/10(6) cells (P less than 0.01), and cAMP-stimulated corticosterone secretion in FC from 2,223 +/- 407 to 414 +/- 58 ng/10(6) cells (P less than 0.01). TMB-8, a putative inhibitor of intracellular calcium mobilization, markedly inhibited (P less than 0.01) cAMP-stimulated aldosterone secretion by GC from 469 +/- 31 to 48 +/- 8 ng/10(6) cells and corticosterone secretion by FC from 9,867 +/- 1,821 to 2,832 +/- 586 ng/10(6) cells. These observations suggest that cAMP activation of adrenal steroidogenesis requires the release of calcium from intracellular stores.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenal Cortex↗